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-rw-r--r--synapse/_scripts/review_recent_signups.py18
-rw-r--r--synapse/api/auth.py13
-rw-r--r--synapse/api/room_versions.py30
-rw-r--r--synapse/app/_base.py3
-rw-r--r--synapse/config/api.py19
-rw-r--r--synapse/config/emailconfig.py24
-rw-r--r--synapse/config/oidc.py9
-rw-r--r--synapse/config/server.py6
-rw-r--r--synapse/config/workers.py24
-rw-r--r--synapse/crypto/keyring.py18
-rw-r--r--synapse/events/snapshot.py18
-rw-r--r--synapse/events/utils.py126
-rw-r--r--synapse/federation/federation_base.py25
-rw-r--r--synapse/federation/federation_client.py5
-rw-r--r--synapse/federation/federation_server.py3
-rw-r--r--synapse/federation/persistence.py3
-rw-r--r--synapse/federation/sender/per_destination_queue.py12
-rw-r--r--synapse/federation/transport/client.py48
-rw-r--r--synapse/handlers/account_data.py2
-rw-r--r--synapse/handlers/admin.py56
-rw-r--r--synapse/handlers/auth.py14
-rw-r--r--synapse/handlers/device.py10
-rw-r--r--synapse/handlers/e2e_keys.py10
-rw-r--r--synapse/handlers/events.py4
-rw-r--r--synapse/handlers/federation.py6
-rw-r--r--synapse/handlers/federation_event.py3
-rw-r--r--synapse/handlers/initial_sync.py16
-rw-r--r--synapse/handlers/message.py2
-rw-r--r--synapse/handlers/pagination.py8
-rw-r--r--synapse/handlers/presence.py2
-rw-r--r--synapse/handlers/register.py12
-rw-r--r--synapse/handlers/room.py24
-rw-r--r--synapse/handlers/room_summary.py36
-rw-r--r--synapse/handlers/search.py10
-rw-r--r--synapse/handlers/sso.py32
-rw-r--r--synapse/handlers/sync.py50
-rw-r--r--synapse/http/connectproxyclient.py4
-rw-r--r--synapse/http/matrixfederationclient.py18
-rw-r--r--synapse/http/site.py4
-rw-r--r--synapse/logging/_remote.py10
-rw-r--r--synapse/logging/context.py20
-rw-r--r--synapse/logging/opentracing.py2
-rw-r--r--synapse/logging/utils.py76
-rw-r--r--synapse/metrics/__init__.py276
-rw-r--r--synapse/metrics/_gc.py203
-rw-r--r--synapse/metrics/_reactor_metrics.py83
-rw-r--r--synapse/notifier.py17
-rw-r--r--synapse/push/__init__.py38
-rw-r--r--synapse/push/bulk_push_rule_evaluator.py18
-rw-r--r--synapse/push/mailer.py4
-rw-r--r--synapse/replication/tcp/streams/events.py34
-rw-r--r--synapse/rest/admin/background_updates.py44
-rw-r--r--synapse/rest/admin/federation.py26
-rw-r--r--synapse/rest/admin/media.py2
-rw-r--r--synapse/rest/admin/rooms.py16
-rw-r--r--synapse/rest/admin/users.py13
-rw-r--r--synapse/rest/client/events.py2
-rw-r--r--synapse/rest/client/notifications.py2
-rw-r--r--synapse/rest/client/relations.py138
-rw-r--r--synapse/rest/client/room.py30
-rw-r--r--synapse/rest/client/sync.py28
-rw-r--r--synapse/rest/media/v1/media_storage.py6
-rw-r--r--synapse/server.py2
-rw-r--r--synapse/state/__init__.py10
-rw-r--r--synapse/storage/database.py62
-rw-r--r--synapse/storage/databases/main/account_data.py6
-rw-r--r--synapse/storage/databases/main/deviceinbox.py30
-rw-r--r--synapse/storage/databases/main/devices.py45
-rw-r--r--synapse/storage/databases/main/directory.py6
-rw-r--r--synapse/storage/databases/main/e2e_room_keys.py34
-rw-r--r--synapse/storage/databases/main/end_to_end_keys.py48
-rw-r--r--synapse/storage/databases/main/event_push_actions.py21
-rw-r--r--synapse/storage/databases/main/events.py145
-rw-r--r--synapse/storage/databases/main/events_bg_updates.py42
-rw-r--r--synapse/storage/databases/main/presence.py33
-rw-r--r--synapse/storage/databases/main/pusher.py8
-rw-r--r--synapse/storage/databases/main/registration.py18
-rw-r--r--synapse/storage/databases/main/relations.py178
-rw-r--r--synapse/storage/databases/main/room.py18
-rw-r--r--synapse/storage/databases/main/roommember.py6
-rw-r--r--synapse/storage/databases/main/session.py1
-rw-r--r--synapse/storage/databases/main/transactions.py11
-rw-r--r--synapse/storage/databases/main/ui_auth.py12
-rw-r--r--synapse/storage/databases/main/user_directory.py12
-rw-r--r--synapse/storage/databases/state/bg_updates.py15
-rw-r--r--synapse/storage/databases/state/store.py27
-rw-r--r--synapse/storage/keys.py6
-rw-r--r--synapse/storage/prepare_database.py6
-rw-r--r--synapse/storage/relations.py20
-rw-r--r--synapse/storage/state.py6
-rw-r--r--synapse/storage/util/id_generators.py8
-rw-r--r--synapse/streams/config.py10
-rw-r--r--synapse/types.py94
-rw-r--r--synapse/util/async_helpers.py6
-rw-r--r--synapse/util/caches/dictionary_cache.py11
95 files changed, 1382 insertions, 1390 deletions
diff --git a/synapse/_scripts/review_recent_signups.py b/synapse/_scripts/review_recent_signups.py
index 093af4327a..e207f154f3 100644
--- a/synapse/_scripts/review_recent_signups.py
+++ b/synapse/_scripts/review_recent_signups.py
@@ -46,7 +46,9 @@ class UserInfo:
     ips: List[str] = attr.Factory(list)
 
 
-def get_recent_users(txn: LoggingTransaction, since_ms: int) -> List[UserInfo]:
+def get_recent_users(
+    txn: LoggingTransaction, since_ms: int, exclude_app_service: bool
+) -> List[UserInfo]:
     """Fetches recently registered users and some info on them."""
 
     sql = """
@@ -56,6 +58,9 @@ def get_recent_users(txn: LoggingTransaction, since_ms: int) -> List[UserInfo]:
             AND deactivated = 0
     """
 
+    if exclude_app_service:
+        sql += " AND appservice_id IS NULL"
+
     txn.execute(sql, (since_ms / 1000,))
 
     user_infos = [UserInfo(user_id, creation_ts) for user_id, creation_ts in txn]
@@ -113,7 +118,7 @@ def main() -> None:
         "-e",
         "--exclude-emails",
         action="store_true",
-        help="Exclude users that have validated email addresses",
+        help="Exclude users that have validated email addresses.",
     )
     parser.add_argument(
         "-u",
@@ -121,6 +126,12 @@ def main() -> None:
         action="store_true",
         help="Only print user IDs that match.",
     )
+    parser.add_argument(
+        "-a",
+        "--exclude-app-service",
+        help="Exclude appservice users.",
+        action="store_true",
+    )
 
     config = ReviewConfig()
 
@@ -133,6 +144,7 @@ def main() -> None:
 
     since_ms = time.time() * 1000 - Config.parse_duration(config_args.since)
     exclude_users_with_email = config_args.exclude_emails
+    exclude_users_with_appservice = config_args.exclude_app_service
     include_context = not config_args.only_users
 
     for database_config in config.database.databases:
@@ -143,7 +155,7 @@ def main() -> None:
 
     with make_conn(database_config, engine, "review_recent_signups") as db_conn:
         # This generates a type of Cursor, not LoggingTransaction.
-        user_infos = get_recent_users(db_conn.cursor(), since_ms)  # type: ignore[arg-type]
+        user_infos = get_recent_users(db_conn.cursor(), since_ms, exclude_users_with_appservice)  # type: ignore[arg-type]
 
     for user_info in user_infos:
         if exclude_users_with_email and user_info.emails:
diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 4a32d430bd..683241201c 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -71,6 +71,7 @@ class Auth:
         self._auth_blocking = AuthBlocking(self.hs)
 
         self._track_appservice_user_ips = hs.config.appservice.track_appservice_user_ips
+        self._track_puppeted_user_ips = hs.config.api.track_puppeted_user_ips
         self._macaroon_secret_key = hs.config.key.macaroon_secret_key
         self._force_tracing_for_users = hs.config.tracing.force_tracing_for_users
 
@@ -246,6 +247,18 @@ class Auth:
                     user_agent=user_agent,
                     device_id=device_id,
                 )
+                # Track also the puppeted user client IP if enabled and the user is puppeting
+                if (
+                    user_info.user_id != user_info.token_owner
+                    and self._track_puppeted_user_ips
+                ):
+                    await self.store.insert_client_ip(
+                        user_id=user_info.user_id,
+                        access_token=access_token,
+                        ip=ip_addr,
+                        user_agent=user_agent,
+                        device_id=device_id,
+                    )
 
             if is_guest and not allow_guest:
                 raise AuthError(
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index 0a895bba48..a747a40814 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -46,41 +46,41 @@ class RoomDisposition:
     UNSTABLE = "unstable"
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class RoomVersion:
     """An object which describes the unique attributes of a room version."""
 
-    identifier = attr.ib(type=str)  # the identifier for this version
-    disposition = attr.ib(type=str)  # one of the RoomDispositions
-    event_format = attr.ib(type=int)  # one of the EventFormatVersions
-    state_res = attr.ib(type=int)  # one of the StateResolutionVersions
-    enforce_key_validity = attr.ib(type=bool)
+    identifier: str  # the identifier for this version
+    disposition: str  # one of the RoomDispositions
+    event_format: int  # one of the EventFormatVersions
+    state_res: int  # one of the StateResolutionVersions
+    enforce_key_validity: bool
 
     # Before MSC2432, m.room.aliases had special auth rules and redaction rules
-    special_case_aliases_auth = attr.ib(type=bool)
+    special_case_aliases_auth: bool
     # Strictly enforce canonicaljson, do not allow:
     # * Integers outside the range of [-2 ^ 53 + 1, 2 ^ 53 - 1]
     # * Floats
     # * NaN, Infinity, -Infinity
-    strict_canonicaljson = attr.ib(type=bool)
+    strict_canonicaljson: bool
     # MSC2209: Check 'notifications' key while verifying
     # m.room.power_levels auth rules.
-    limit_notifications_power_levels = attr.ib(type=bool)
+    limit_notifications_power_levels: bool
     # MSC2174/MSC2176: Apply updated redaction rules algorithm.
-    msc2176_redaction_rules = attr.ib(type=bool)
+    msc2176_redaction_rules: bool
     # MSC3083: Support the 'restricted' join_rule.
-    msc3083_join_rules = attr.ib(type=bool)
+    msc3083_join_rules: bool
     # MSC3375: Support for the proper redaction rules for MSC3083. This mustn't
     #          be enabled if MSC3083 is not.
-    msc3375_redaction_rules = attr.ib(type=bool)
+    msc3375_redaction_rules: bool
     # MSC2403: Allows join_rules to be set to 'knock', changes auth rules to allow sending
     # m.room.membership event with membership 'knock'.
-    msc2403_knocking = attr.ib(type=bool)
+    msc2403_knocking: bool
     # MSC2716: Adds m.room.power_levels -> content.historical field to control
     # whether "insertion", "chunk", "marker" events can be sent
-    msc2716_historical = attr.ib(type=bool)
+    msc2716_historical: bool
     # MSC2716: Adds support for redacting "insertion", "chunk", and "marker" events
-    msc2716_redactions = attr.ib(type=bool)
+    msc2716_redactions: bool
 
 
 class RoomVersions:
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 5fc59c1be1..579adbbca0 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -60,7 +60,7 @@ from synapse.events.spamcheck import load_legacy_spam_checkers
 from synapse.events.third_party_rules import load_legacy_third_party_event_rules
 from synapse.handlers.auth import load_legacy_password_auth_providers
 from synapse.logging.context import PreserveLoggingContext
-from synapse.metrics import register_threadpool
+from synapse.metrics import install_gc_manager, register_threadpool
 from synapse.metrics.background_process_metrics import wrap_as_background_process
 from synapse.metrics.jemalloc import setup_jemalloc_stats
 from synapse.types import ISynapseReactor
@@ -159,6 +159,7 @@ def start_reactor(
         change_resource_limit(soft_file_limit)
         if gc_thresholds:
             gc.set_threshold(*gc_thresholds)
+        install_gc_manager()
         run_command()
 
     # make sure that we run the reactor with the sentinel log context,
diff --git a/synapse/config/api.py b/synapse/config/api.py
index 25538b82d5..8133b6b624 100644
--- a/synapse/config/api.py
+++ b/synapse/config/api.py
@@ -29,6 +29,7 @@ class ApiConfig(Config):
     def read_config(self, config: JsonDict, **kwargs):
         validate_config(_MAIN_SCHEMA, config, ())
         self.room_prejoin_state = list(self._get_prejoin_state_types(config))
+        self.track_puppeted_user_ips = config.get("track_puppeted_user_ips", False)
 
     def generate_config_section(cls, **kwargs) -> str:
         formatted_default_state_types = "\n".join(
@@ -59,6 +60,21 @@ class ApiConfig(Config):
            #
            #additional_event_types:
            #  - org.example.custom.event.type
+
+        # We record the IP address of clients used to access the API for various
+        # reasons, including displaying it to the user in the "Where you're signed in"
+        # dialog.
+        #
+        # By default, when puppeting another user via the admin API, the client IP
+        # address is recorded against the user who created the access token (ie, the
+        # admin user), and *not* the puppeted user.
+        #
+        # Uncomment the following to also record the IP address against the puppeted
+        # user. (This also means that the puppeted user will count as an "active" user
+        # for the purpose of monthly active user tracking - see 'limit_usage_by_mau' etc
+        # above.)
+        #
+        #track_puppeted_user_ips: true
         """ % {
             "formatted_default_state_types": formatted_default_state_types
         }
@@ -138,5 +154,8 @@ _MAIN_SCHEMA = {
     "properties": {
         "room_prejoin_state": _ROOM_PREJOIN_STATE_CONFIG_SCHEMA,
         "room_invite_state_types": _ROOM_INVITE_STATE_TYPES_SCHEMA,
+        "track_puppeted_user_ips": {
+            "type": "boolean",
+        },
     },
 }
diff --git a/synapse/config/emailconfig.py b/synapse/config/emailconfig.py
index 510b647c63..949d7dd5ac 100644
--- a/synapse/config/emailconfig.py
+++ b/synapse/config/emailconfig.py
@@ -55,19 +55,19 @@ https://matrix-org.github.io/synapse/latest/templates.html
 ---------------------------------------------------------------------------------------"""
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class EmailSubjectConfig:
-    message_from_person_in_room = attr.ib(type=str)
-    message_from_person = attr.ib(type=str)
-    messages_from_person = attr.ib(type=str)
-    messages_in_room = attr.ib(type=str)
-    messages_in_room_and_others = attr.ib(type=str)
-    messages_from_person_and_others = attr.ib(type=str)
-    invite_from_person = attr.ib(type=str)
-    invite_from_person_to_room = attr.ib(type=str)
-    invite_from_person_to_space = attr.ib(type=str)
-    password_reset = attr.ib(type=str)
-    email_validation = attr.ib(type=str)
+    message_from_person_in_room: str
+    message_from_person: str
+    messages_from_person: str
+    messages_in_room: str
+    messages_in_room_and_others: str
+    messages_from_person_and_others: str
+    invite_from_person: str
+    invite_from_person_to_room: str
+    invite_from_person_to_space: str
+    password_reset: str
+    email_validation: str
 
 
 class EmailConfig(Config):
diff --git a/synapse/config/oidc.py b/synapse/config/oidc.py
index 79c400fe30..e783b11315 100644
--- a/synapse/config/oidc.py
+++ b/synapse/config/oidc.py
@@ -148,10 +148,13 @@ class OIDCConfig(Config):
         #       Defaults to false. Avoid this in production.
         #
         #   user_profile_method: Whether to fetch the user profile from the userinfo
-        #       endpoint. Valid values are: 'auto' or 'userinfo_endpoint'.
+        #       endpoint, or to rely on the data returned in the id_token from the
+        #       token_endpoint.
         #
-        #       Defaults to 'auto', which fetches the userinfo endpoint if 'openid' is
-        #       included in 'scopes'. Set to 'userinfo_endpoint' to always fetch the
+        #       Valid values are: 'auto' or 'userinfo_endpoint'.
+        #
+        #       Defaults to 'auto', which uses the userinfo endpoint if 'openid' is
+        #       not included in 'scopes'. Set to 'userinfo_endpoint' to always use the
         #       userinfo endpoint.
         #
         #   allow_existing_users: set to 'true' to allow a user logging in via OIDC to
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 1de2dea9b0..5010266b69 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -200,8 +200,8 @@ class HttpListenerConfig:
     """Object describing the http-specific parts of the config of a listener"""
 
     x_forwarded: bool = False
-    resources: List[HttpResourceConfig] = attr.ib(factory=list)
-    additional_resources: Dict[str, dict] = attr.ib(factory=dict)
+    resources: List[HttpResourceConfig] = attr.Factory(list)
+    additional_resources: Dict[str, dict] = attr.Factory(dict)
     tag: Optional[str] = None
 
 
@@ -883,7 +883,7 @@ class ServerConfig(Config):
         # The default room version for newly created rooms.
         #
         # Known room versions are listed here:
-        # https://matrix.org/docs/spec/#complete-list-of-room-versions
+        # https://spec.matrix.org/latest/rooms/#complete-list-of-room-versions
         #
         # For example, for room version 1, default_room_version should be set
         # to "1".
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index 576f519188..bdaba6db37 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -51,12 +51,12 @@ def _instance_to_list_converter(obj: Union[str, List[str]]) -> List[str]:
     return obj
 
 
-@attr.s
+@attr.s(auto_attribs=True)
 class InstanceLocationConfig:
     """The host and port to talk to an instance via HTTP replication."""
 
-    host = attr.ib(type=str)
-    port = attr.ib(type=int)
+    host: str
+    port: int
 
 
 @attr.s
@@ -77,34 +77,28 @@ class WriterLocations:
             can only be a single instance.
     """
 
-    events = attr.ib(
+    events: List[str] = attr.ib(
         default=["master"],
-        type=List[str],
         converter=_instance_to_list_converter,
     )
-    typing = attr.ib(
+    typing: List[str] = attr.ib(
         default=["master"],
-        type=List[str],
         converter=_instance_to_list_converter,
     )
-    to_device = attr.ib(
+    to_device: List[str] = attr.ib(
         default=["master"],
-        type=List[str],
         converter=_instance_to_list_converter,
     )
-    account_data = attr.ib(
+    account_data: List[str] = attr.ib(
         default=["master"],
-        type=List[str],
         converter=_instance_to_list_converter,
     )
-    receipts = attr.ib(
+    receipts: List[str] = attr.ib(
         default=["master"],
-        type=List[str],
         converter=_instance_to_list_converter,
     )
-    presence = attr.ib(
+    presence: List[str] = attr.ib(
         default=["master"],
-        type=List[str],
         converter=_instance_to_list_converter,
     )
 
diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index 993b04099e..72d4a69aac 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -58,7 +58,7 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
-@attr.s(slots=True, cmp=False)
+@attr.s(slots=True, frozen=True, cmp=False, auto_attribs=True)
 class VerifyJsonRequest:
     """
     A request to verify a JSON object.
@@ -78,10 +78,10 @@ class VerifyJsonRequest:
         key_ids: The set of key_ids to that could be used to verify the JSON object
     """
 
-    server_name = attr.ib(type=str)
-    get_json_object = attr.ib(type=Callable[[], JsonDict])
-    minimum_valid_until_ts = attr.ib(type=int)
-    key_ids = attr.ib(type=List[str])
+    server_name: str
+    get_json_object: Callable[[], JsonDict]
+    minimum_valid_until_ts: int
+    key_ids: List[str]
 
     @staticmethod
     def from_json_object(
@@ -124,7 +124,7 @@ class KeyLookupError(ValueError):
     pass
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class _FetchKeyRequest:
     """A request for keys for a given server.
 
@@ -138,9 +138,9 @@ class _FetchKeyRequest:
         key_ids: The IDs of the keys to attempt to fetch
     """
 
-    server_name = attr.ib(type=str)
-    minimum_valid_until_ts = attr.ib(type=int)
-    key_ids = attr.ib(type=List[str])
+    server_name: str
+    minimum_valid_until_ts: int
+    key_ids: List[str]
 
 
 class Keyring:
diff --git a/synapse/events/snapshot.py b/synapse/events/snapshot.py
index f251402ed8..0eab1aefd6 100644
--- a/synapse/events/snapshot.py
+++ b/synapse/events/snapshot.py
@@ -28,7 +28,7 @@ if TYPE_CHECKING:
     from synapse.storage.databases.main import DataStore
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class EventContext:
     """
     Holds information relevant to persisting an event
@@ -103,15 +103,15 @@ class EventContext:
             accessed via get_prev_state_ids.
     """
 
-    rejected = attr.ib(default=False, type=Union[bool, str])
-    _state_group = attr.ib(default=None, type=Optional[int])
-    state_group_before_event = attr.ib(default=None, type=Optional[int])
-    prev_group = attr.ib(default=None, type=Optional[int])
-    delta_ids = attr.ib(default=None, type=Optional[StateMap[str]])
-    app_service = attr.ib(default=None, type=Optional[ApplicationService])
+    rejected: Union[bool, str] = False
+    _state_group: Optional[int] = None
+    state_group_before_event: Optional[int] = None
+    prev_group: Optional[int] = None
+    delta_ids: Optional[StateMap[str]] = None
+    app_service: Optional[ApplicationService] = None
 
-    _current_state_ids = attr.ib(default=None, type=Optional[StateMap[str]])
-    _prev_state_ids = attr.ib(default=None, type=Optional[StateMap[str]])
+    _current_state_ids: Optional[StateMap[str]] = None
+    _prev_state_ids: Optional[StateMap[str]] = None
 
     @staticmethod
     def with_state(
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 2038e72924..de0e0c1731 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -14,17 +14,7 @@
 # limitations under the License.
 import collections.abc
 import re
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Callable,
-    Dict,
-    Iterable,
-    List,
-    Mapping,
-    Optional,
-    Union,
-)
+from typing import Any, Callable, Dict, Iterable, List, Mapping, Optional, Union
 
 from frozendict import frozendict
 
@@ -32,14 +22,10 @@ from synapse.api.constants import EventContentFields, EventTypes, RelationTypes
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.types import JsonDict
-from synapse.util.async_helpers import yieldable_gather_results
 from synapse.util.frozenutils import unfreeze
 
 from . import EventBase
 
-if TYPE_CHECKING:
-    from synapse.server import HomeServer
-
 # Split strings on "." but not "\." This uses a negative lookbehind assertion for '\'
 # (?<!stuff) matches if the current position in the string is not preceded
 # by a match for 'stuff'.
@@ -385,17 +371,12 @@ class EventClientSerializer:
     clients.
     """
 
-    def __init__(self, hs: "HomeServer"):
-        self.store = hs.get_datastore()
-        self._msc1849_enabled = hs.config.experimental.msc1849_enabled
-        self._msc3440_enabled = hs.config.experimental.msc3440_enabled
-
-    async def serialize_event(
+    def serialize_event(
         self,
         event: Union[JsonDict, EventBase],
         time_now: int,
         *,
-        bundle_aggregations: bool = False,
+        bundle_aggregations: Optional[Dict[str, JsonDict]] = None,
         **kwargs: Any,
     ) -> JsonDict:
         """Serializes a single event.
@@ -418,66 +399,41 @@ class EventClientSerializer:
         serialized_event = serialize_event(event, time_now, **kwargs)
 
         # Check if there are any bundled aggregations to include with the event.
-        #
-        # Do not bundle aggregations if any of the following at true:
-        #
-        # * Support is disabled via the configuration or the caller.
-        # * The event is a state event.
-        # * The event has been redacted.
-        if (
-            self._msc1849_enabled
-            and bundle_aggregations
-            and not event.is_state()
-            and not event.internal_metadata.is_redacted()
-        ):
-            await self._injected_bundled_aggregations(event, time_now, serialized_event)
+        if bundle_aggregations:
+            event_aggregations = bundle_aggregations.get(event.event_id)
+            if event_aggregations:
+                self._injected_bundled_aggregations(
+                    event,
+                    time_now,
+                    bundle_aggregations[event.event_id],
+                    serialized_event,
+                )
 
         return serialized_event
 
-    async def _injected_bundled_aggregations(
-        self, event: EventBase, time_now: int, serialized_event: JsonDict
+    def _injected_bundled_aggregations(
+        self,
+        event: EventBase,
+        time_now: int,
+        aggregations: JsonDict,
+        serialized_event: JsonDict,
     ) -> None:
         """Potentially injects bundled aggregations into the unsigned portion of the serialized event.
 
         Args:
             event: The event being serialized.
             time_now: The current time in milliseconds
+            aggregations: The bundled aggregation to serialize.
             serialized_event: The serialized event which may be modified.
 
         """
-        # Do not bundle aggregations for an event which represents an edit or an
-        # annotation. It does not make sense for them to have related events.
-        relates_to = event.content.get("m.relates_to")
-        if isinstance(relates_to, (dict, frozendict)):
-            relation_type = relates_to.get("rel_type")
-            if relation_type in (RelationTypes.ANNOTATION, RelationTypes.REPLACE):
-                return
-
-        event_id = event.event_id
-        room_id = event.room_id
-
-        # The bundled aggregations to include.
-        aggregations = {}
-
-        annotations = await self.store.get_aggregation_groups_for_event(
-            event_id, room_id
-        )
-        if annotations.chunk:
-            aggregations[RelationTypes.ANNOTATION] = annotations.to_dict()
+        # Make a copy in-case the object is cached.
+        aggregations = aggregations.copy()
 
-        references = await self.store.get_relations_for_event(
-            event_id, room_id, RelationTypes.REFERENCE, direction="f"
-        )
-        if references.chunk:
-            aggregations[RelationTypes.REFERENCE] = references.to_dict()
-
-        edit = None
-        if event.type == EventTypes.Message:
-            edit = await self.store.get_applicable_edit(event_id, room_id)
-
-        if edit:
+        if RelationTypes.REPLACE in aggregations:
             # If there is an edit replace the content, preserving existing
             # relations.
+            edit = aggregations[RelationTypes.REPLACE]
 
             # Ensure we take copies of the edit content, otherwise we risk modifying
             # the original event.
@@ -502,27 +458,19 @@ class EventClientSerializer:
             }
 
         # If this event is the start of a thread, include a summary of the replies.
-        if self._msc3440_enabled:
-            (
-                thread_count,
-                latest_thread_event,
-            ) = await self.store.get_thread_summary(event_id, room_id)
-            if latest_thread_event:
-                aggregations[RelationTypes.THREAD] = {
-                    # Don't bundle aggregations as this could recurse forever.
-                    "latest_event": await self.serialize_event(
-                        latest_thread_event, time_now, bundle_aggregations=False
-                    ),
-                    "count": thread_count,
-                }
-
-        # If any bundled aggregations were found, include them.
-        if aggregations:
-            serialized_event["unsigned"].setdefault("m.relations", {}).update(
-                aggregations
+        if RelationTypes.THREAD in aggregations:
+            # Serialize the latest thread event.
+            latest_thread_event = aggregations[RelationTypes.THREAD]["latest_event"]
+
+            # Don't bundle aggregations as this could recurse forever.
+            aggregations[RelationTypes.THREAD]["latest_event"] = self.serialize_event(
+                latest_thread_event, time_now, bundle_aggregations=None
             )
 
-    async def serialize_events(
+        # Include the bundled aggregations in the event.
+        serialized_event["unsigned"].setdefault("m.relations", {}).update(aggregations)
+
+    def serialize_events(
         self, events: Iterable[Union[JsonDict, EventBase]], time_now: int, **kwargs: Any
     ) -> List[JsonDict]:
         """Serializes multiple events.
@@ -535,9 +483,9 @@ class EventClientSerializer:
         Returns:
             The list of serialized events
         """
-        return await yieldable_gather_results(
-            self.serialize_event, events, time_now=time_now, **kwargs
-        )
+        return [
+            self.serialize_event(event, time_now=time_now, **kwargs) for event in events
+        ]
 
 
 def copy_power_levels_contents(
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index addc0bf000..896168c05c 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -230,6 +230,10 @@ def event_from_pdu_json(pdu_json: JsonDict, room_version: RoomVersion) -> EventB
     # origin, etc etc)
     assert_params_in_dict(pdu_json, ("type", "depth"))
 
+    # Strip any unauthorized values from "unsigned" if they exist
+    if "unsigned" in pdu_json:
+        _strip_unsigned_values(pdu_json)
+
     depth = pdu_json["depth"]
     if not isinstance(depth, int):
         raise SynapseError(400, "Depth %r not an intger" % (depth,), Codes.BAD_JSON)
@@ -245,3 +249,24 @@ def event_from_pdu_json(pdu_json: JsonDict, room_version: RoomVersion) -> EventB
 
     event = make_event_from_dict(pdu_json, room_version)
     return event
+
+
+def _strip_unsigned_values(pdu_dict: JsonDict) -> None:
+    """
+    Strip any unsigned values unless specifically allowed, as defined by the whitelist.
+
+    pdu: the json dict to strip values from. Note that the dict is mutated by this
+    function
+    """
+    unsigned = pdu_dict["unsigned"]
+
+    if not isinstance(unsigned, dict):
+        pdu_dict["unsigned"] = {}
+
+    if pdu_dict["type"] == "m.room.member":
+        whitelist = ["knock_room_state", "invite_room_state", "age"]
+    else:
+        whitelist = ["age"]
+
+    filtered_unsigned = {k: v for k, v in unsigned.items() if k in whitelist}
+    pdu_dict["unsigned"] = filtered_unsigned
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 6ea4edfc71..57cf35bd92 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -56,7 +56,6 @@ from synapse.api.room_versions import (
 from synapse.events import EventBase, builder
 from synapse.federation.federation_base import FederationBase, event_from_pdu_json
 from synapse.federation.transport.client import SendJoinResponse
-from synapse.logging.utils import log_function
 from synapse.types import JsonDict, get_domain_from_id
 from synapse.util.async_helpers import concurrently_execute
 from synapse.util.caches.expiringcache import ExpiringCache
@@ -144,7 +143,6 @@ class FederationClient(FederationBase):
             if destination_dict:
                 self.pdu_destination_tried[event_id] = destination_dict
 
-    @log_function
     async def make_query(
         self,
         destination: str,
@@ -178,7 +176,6 @@ class FederationClient(FederationBase):
             ignore_backoff=ignore_backoff,
         )
 
-    @log_function
     async def query_client_keys(
         self, destination: str, content: JsonDict, timeout: int
     ) -> JsonDict:
@@ -196,7 +193,6 @@ class FederationClient(FederationBase):
             destination, content, timeout
         )
 
-    @log_function
     async def query_user_devices(
         self, destination: str, user_id: str, timeout: int = 30000
     ) -> JsonDict:
@@ -208,7 +204,6 @@ class FederationClient(FederationBase):
             destination, user_id, timeout
         )
 
-    @log_function
     async def claim_client_keys(
         self, destination: str, content: JsonDict, timeout: int
     ) -> JsonDict:
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index ee71f289c8..af9cb98f67 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -58,7 +58,6 @@ from synapse.logging.context import (
     run_in_background,
 )
 from synapse.logging.opentracing import log_kv, start_active_span_from_edu, trace
-from synapse.logging.utils import log_function
 from synapse.metrics.background_process_metrics import wrap_as_background_process
 from synapse.replication.http.federation import (
     ReplicationFederationSendEduRestServlet,
@@ -859,7 +858,6 @@ class FederationServer(FederationBase):
             res = {"auth_chain": [a.get_pdu_json(time_now) for a in auth_pdus]}
         return 200, res
 
-    @log_function
     async def on_query_client_keys(
         self, origin: str, content: Dict[str, str]
     ) -> Tuple[int, Dict[str, Any]]:
@@ -940,7 +938,6 @@ class FederationServer(FederationBase):
 
         return {"events": [ev.get_pdu_json(time_now) for ev in missing_events]}
 
-    @log_function
     async def on_openid_userinfo(self, token: str) -> Optional[str]:
         ts_now_ms = self._clock.time_msec()
         return await self.store.get_user_id_for_open_id_token(token, ts_now_ms)
diff --git a/synapse/federation/persistence.py b/synapse/federation/persistence.py
index 523ab1c51e..60e2e6cf01 100644
--- a/synapse/federation/persistence.py
+++ b/synapse/federation/persistence.py
@@ -23,7 +23,6 @@ import logging
 from typing import Optional, Tuple
 
 from synapse.federation.units import Transaction
-from synapse.logging.utils import log_function
 from synapse.storage.databases.main import DataStore
 from synapse.types import JsonDict
 
@@ -36,7 +35,6 @@ class TransactionActions:
     def __init__(self, datastore: DataStore):
         self.store = datastore
 
-    @log_function
     async def have_responded(
         self, origin: str, transaction: Transaction
     ) -> Optional[Tuple[int, JsonDict]]:
@@ -53,7 +51,6 @@ class TransactionActions:
 
         return await self.store.get_received_txn_response(transaction_id, origin)
 
-    @log_function
     async def set_response(
         self, origin: str, transaction: Transaction, code: int, response: JsonDict
     ) -> None:
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index 391b30fbb5..8152e80b88 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -607,18 +607,18 @@ class PerDestinationQueue:
         self._pending_pdus = []
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _TransactionQueueManager:
     """A helper async context manager for pulling stuff off the queues and
     tracking what was last successfully sent, etc.
     """
 
-    queue = attr.ib(type=PerDestinationQueue)
+    queue: PerDestinationQueue
 
-    _device_stream_id = attr.ib(type=Optional[int], default=None)
-    _device_list_id = attr.ib(type=Optional[int], default=None)
-    _last_stream_ordering = attr.ib(type=Optional[int], default=None)
-    _pdus = attr.ib(type=List[EventBase], factory=list)
+    _device_stream_id: Optional[int] = None
+    _device_list_id: Optional[int] = None
+    _last_stream_ordering: Optional[int] = None
+    _pdus: List[EventBase] = attr.Factory(list)
 
     async def __aenter__(self) -> Tuple[List[EventBase], List[Edu]]:
         # First we calculate the EDUs we want to send, if any.
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 9fc4c31c93..8782586cd6 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -44,7 +44,6 @@ from synapse.api.urls import (
 from synapse.events import EventBase, make_event_from_dict
 from synapse.federation.units import Transaction
 from synapse.http.matrixfederationclient import ByteParser
-from synapse.logging.utils import log_function
 from synapse.types import JsonDict
 
 logger = logging.getLogger(__name__)
@@ -62,7 +61,6 @@ class TransportLayerClient:
         self.server_name = hs.hostname
         self.client = hs.get_federation_http_client()
 
-    @log_function
     async def get_room_state_ids(
         self, destination: str, room_id: str, event_id: str
     ) -> JsonDict:
@@ -88,7 +86,6 @@ class TransportLayerClient:
             try_trailing_slash_on_400=True,
         )
 
-    @log_function
     async def get_event(
         self, destination: str, event_id: str, timeout: Optional[int] = None
     ) -> JsonDict:
@@ -111,7 +108,6 @@ class TransportLayerClient:
             destination, path=path, timeout=timeout, try_trailing_slash_on_400=True
         )
 
-    @log_function
     async def backfill(
         self, destination: str, room_id: str, event_tuples: Collection[str], limit: int
     ) -> Optional[JsonDict]:
@@ -149,7 +145,6 @@ class TransportLayerClient:
             destination, path=path, args=args, try_trailing_slash_on_400=True
         )
 
-    @log_function
     async def timestamp_to_event(
         self, destination: str, room_id: str, timestamp: int, direction: str
     ) -> Union[JsonDict, List]:
@@ -185,7 +180,6 @@ class TransportLayerClient:
 
         return remote_response
 
-    @log_function
     async def send_transaction(
         self,
         transaction: Transaction,
@@ -234,7 +228,6 @@ class TransportLayerClient:
             try_trailing_slash_on_400=True,
         )
 
-    @log_function
     async def make_query(
         self,
         destination: str,
@@ -254,7 +247,6 @@ class TransportLayerClient:
             ignore_backoff=ignore_backoff,
         )
 
-    @log_function
     async def make_membership_event(
         self,
         destination: str,
@@ -317,7 +309,6 @@ class TransportLayerClient:
             ignore_backoff=ignore_backoff,
         )
 
-    @log_function
     async def send_join_v1(
         self,
         room_version: RoomVersion,
@@ -336,7 +327,6 @@ class TransportLayerClient:
             max_response_size=MAX_RESPONSE_SIZE_SEND_JOIN,
         )
 
-    @log_function
     async def send_join_v2(
         self,
         room_version: RoomVersion,
@@ -355,7 +345,6 @@ class TransportLayerClient:
             max_response_size=MAX_RESPONSE_SIZE_SEND_JOIN,
         )
 
-    @log_function
     async def send_leave_v1(
         self, destination: str, room_id: str, event_id: str, content: JsonDict
     ) -> Tuple[int, JsonDict]:
@@ -372,7 +361,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def send_leave_v2(
         self, destination: str, room_id: str, event_id: str, content: JsonDict
     ) -> JsonDict:
@@ -389,7 +377,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def send_knock_v1(
         self,
         destination: str,
@@ -423,7 +410,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content
         )
 
-    @log_function
     async def send_invite_v1(
         self, destination: str, room_id: str, event_id: str, content: JsonDict
     ) -> Tuple[int, JsonDict]:
@@ -433,7 +419,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     async def send_invite_v2(
         self, destination: str, room_id: str, event_id: str, content: JsonDict
     ) -> JsonDict:
@@ -443,7 +428,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     async def get_public_rooms(
         self,
         remote_server: str,
@@ -516,7 +500,6 @@ class TransportLayerClient:
 
         return response
 
-    @log_function
     async def exchange_third_party_invite(
         self, destination: str, room_id: str, event_dict: JsonDict
     ) -> JsonDict:
@@ -526,7 +509,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=event_dict
         )
 
-    @log_function
     async def get_event_auth(
         self, destination: str, room_id: str, event_id: str
     ) -> JsonDict:
@@ -534,7 +516,6 @@ class TransportLayerClient:
 
         return await self.client.get_json(destination=destination, path=path)
 
-    @log_function
     async def query_client_keys(
         self, destination: str, query_content: JsonDict, timeout: int
     ) -> JsonDict:
@@ -576,7 +557,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=query_content, timeout=timeout
         )
 
-    @log_function
     async def query_user_devices(
         self, destination: str, user_id: str, timeout: int
     ) -> JsonDict:
@@ -616,7 +596,6 @@ class TransportLayerClient:
             destination=destination, path=path, timeout=timeout
         )
 
-    @log_function
     async def claim_client_keys(
         self, destination: str, query_content: JsonDict, timeout: int
     ) -> JsonDict:
@@ -655,7 +634,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=query_content, timeout=timeout
         )
 
-    @log_function
     async def get_missing_events(
         self,
         destination: str,
@@ -680,7 +658,6 @@ class TransportLayerClient:
             timeout=timeout,
         )
 
-    @log_function
     async def get_group_profile(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -694,7 +671,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def update_group_profile(
         self, destination: str, group_id: str, requester_user_id: str, content: JsonDict
     ) -> JsonDict:
@@ -716,7 +692,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_group_summary(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -730,7 +705,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_rooms_in_group(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -798,7 +772,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_users_in_group(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -812,7 +785,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_invited_users_in_group(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -826,7 +798,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def accept_group_invite(
         self, destination: str, group_id: str, user_id: str, content: JsonDict
     ) -> JsonDict:
@@ -837,7 +808,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     def join_group(
         self, destination: str, group_id: str, user_id: str, content: JsonDict
     ) -> Awaitable[JsonDict]:
@@ -848,7 +818,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     async def invite_to_group(
         self,
         destination: str,
@@ -868,7 +837,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def invite_to_group_notification(
         self, destination: str, group_id: str, user_id: str, content: JsonDict
     ) -> JsonDict:
@@ -882,7 +850,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     async def remove_user_from_group(
         self,
         destination: str,
@@ -902,7 +869,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def remove_user_from_group_notification(
         self, destination: str, group_id: str, user_id: str, content: JsonDict
     ) -> JsonDict:
@@ -916,7 +882,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     async def renew_group_attestation(
         self, destination: str, group_id: str, user_id: str, content: JsonDict
     ) -> JsonDict:
@@ -930,7 +895,6 @@ class TransportLayerClient:
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
-    @log_function
     async def update_group_summary_room(
         self,
         destination: str,
@@ -959,7 +923,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def delete_group_summary_room(
         self,
         destination: str,
@@ -986,7 +949,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_group_categories(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -1000,7 +962,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_group_category(
         self, destination: str, group_id: str, requester_user_id: str, category_id: str
     ) -> JsonDict:
@@ -1014,7 +975,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def update_group_category(
         self,
         destination: str,
@@ -1034,7 +994,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def delete_group_category(
         self, destination: str, group_id: str, requester_user_id: str, category_id: str
     ) -> JsonDict:
@@ -1048,7 +1007,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_group_roles(
         self, destination: str, group_id: str, requester_user_id: str
     ) -> JsonDict:
@@ -1062,7 +1020,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def get_group_role(
         self, destination: str, group_id: str, requester_user_id: str, role_id: str
     ) -> JsonDict:
@@ -1076,7 +1033,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def update_group_role(
         self,
         destination: str,
@@ -1096,7 +1052,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def delete_group_role(
         self, destination: str, group_id: str, requester_user_id: str, role_id: str
     ) -> JsonDict:
@@ -1110,7 +1065,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def update_group_summary_user(
         self,
         destination: str,
@@ -1136,7 +1090,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def set_group_join_policy(
         self, destination: str, group_id: str, requester_user_id: str, content: JsonDict
     ) -> JsonDict:
@@ -1151,7 +1104,6 @@ class TransportLayerClient:
             ignore_backoff=True,
         )
 
-    @log_function
     async def delete_group_summary_user(
         self,
         destination: str,
diff --git a/synapse/handlers/account_data.py b/synapse/handlers/account_data.py
index 96273e2f81..bad48713bc 100644
--- a/synapse/handlers/account_data.py
+++ b/synapse/handlers/account_data.py
@@ -77,7 +77,7 @@ class AccountDataHandler:
     async def add_account_data_for_user(
         self, user_id: str, account_data_type: str, content: JsonDict
     ) -> int:
-        """Add some account_data to a room for a user.
+        """Add some global account_data for a user.
 
         Args:
             user_id: The user to add a tag for.
diff --git a/synapse/handlers/admin.py b/synapse/handlers/admin.py
index 85157a138b..00ab5e79bf 100644
--- a/synapse/handlers/admin.py
+++ b/synapse/handlers/admin.py
@@ -55,21 +55,47 @@ class AdminHandler:
 
     async def get_user(self, user: UserID) -> Optional[JsonDict]:
         """Function to get user details"""
-        ret = await self.store.get_user_by_id(user.to_string())
-        if ret:
-            profile = await self.store.get_profileinfo(user.localpart)
-            threepids = await self.store.user_get_threepids(user.to_string())
-            external_ids = [
-                ({"auth_provider": auth_provider, "external_id": external_id})
-                for auth_provider, external_id in await self.store.get_external_ids_by_user(
-                    user.to_string()
-                )
-            ]
-            ret["displayname"] = profile.display_name
-            ret["avatar_url"] = profile.avatar_url
-            ret["threepids"] = threepids
-            ret["external_ids"] = external_ids
-        return ret
+        user_info_dict = await self.store.get_user_by_id(user.to_string())
+        if user_info_dict is None:
+            return None
+
+        # Restrict returned information to a known set of fields. This prevents additional
+        # fields added to get_user_by_id from modifying Synapse's external API surface.
+        user_info_to_return = {
+            "name",
+            "admin",
+            "deactivated",
+            "shadow_banned",
+            "creation_ts",
+            "appservice_id",
+            "consent_server_notice_sent",
+            "consent_version",
+            "user_type",
+            "is_guest",
+        }
+
+        # Restrict returned keys to a known set.
+        user_info_dict = {
+            key: value
+            for key, value in user_info_dict.items()
+            if key in user_info_to_return
+        }
+
+        # Add additional user metadata
+        profile = await self.store.get_profileinfo(user.localpart)
+        threepids = await self.store.user_get_threepids(user.to_string())
+        external_ids = [
+            ({"auth_provider": auth_provider, "external_id": external_id})
+            for auth_provider, external_id in await self.store.get_external_ids_by_user(
+                user.to_string()
+            )
+        ]
+        user_info_dict["displayname"] = profile.display_name
+        user_info_dict["avatar_url"] = profile.avatar_url
+        user_info_dict["threepids"] = threepids
+        user_info_dict["external_ids"] = external_ids
+
+        return user_info_dict
 
     async def export_user_data(self, user_id: str, writer: "ExfiltrationWriter") -> Any:
         """Write all data we have on the user to the given writer.
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 84724b207c..2389c9ac52 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -168,25 +168,25 @@ def login_id_phone_to_thirdparty(identifier: JsonDict) -> Dict[str, str]:
     }
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class SsoLoginExtraAttributes:
     """Data we track about SAML2 sessions"""
 
     # time the session was created, in milliseconds
-    creation_time = attr.ib(type=int)
-    extra_attributes = attr.ib(type=JsonDict)
+    creation_time: int
+    extra_attributes: JsonDict
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class LoginTokenAttributes:
     """Data we store in a short-term login token"""
 
-    user_id = attr.ib(type=str)
+    user_id: str
 
-    auth_provider_id = attr.ib(type=str)
+    auth_provider_id: str
     """The SSO Identity Provider that the user authenticated with, to get this token."""
 
-    auth_provider_session_id = attr.ib(type=Optional[str])
+    auth_provider_session_id: Optional[str]
     """The session ID advertised by the SSO Identity Provider."""
 
 
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 7665425232..b184a48cb1 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -948,8 +948,16 @@ class DeviceListUpdater:
             devices = []
             ignore_devices = True
         else:
+            prev_stream_id = await self.store.get_device_list_last_stream_id_for_remote(
+                user_id
+            )
             cached_devices = await self.store.get_cached_devices_for_user(user_id)
-            if cached_devices == {d["device_id"]: d for d in devices}:
+
+            # To ensure that a user with no devices is cached, we skip the resync only
+            # if we have a stream_id from previously writing a cache entry.
+            if prev_stream_id is not None and cached_devices == {
+                d["device_id"]: d for d in devices
+            }:
                 logging.info(
                     "Skipping device list resync for %s, as our cache matches already",
                     user_id,
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 14360b4e40..d4dfddf63f 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -1321,14 +1321,14 @@ def _one_time_keys_match(old_key_json: str, new_key: JsonDict) -> bool:
     return old_key == new_key_copy
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class SignatureListItem:
     """An item in the signature list as used by upload_signatures_for_device_keys."""
 
-    signing_key_id = attr.ib(type=str)
-    target_user_id = attr.ib(type=str)
-    target_device_id = attr.ib(type=str)
-    signature = attr.ib(type=JsonDict)
+    signing_key_id: str
+    target_user_id: str
+    target_device_id: str
+    signature: JsonDict
 
 
 class SigningKeyEduUpdater:
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index 1b996c420d..bac5de0526 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -20,7 +20,6 @@ from synapse.api.constants import EduTypes, EventTypes, Membership
 from synapse.api.errors import AuthError, SynapseError
 from synapse.events import EventBase
 from synapse.handlers.presence import format_user_presence_state
-from synapse.logging.utils import log_function
 from synapse.streams.config import PaginationConfig
 from synapse.types import JsonDict, UserID
 from synapse.visibility import filter_events_for_client
@@ -43,7 +42,6 @@ class EventStreamHandler:
         self._server_notices_sender = hs.get_server_notices_sender()
         self._event_serializer = hs.get_event_client_serializer()
 
-    @log_function
     async def get_stream(
         self,
         auth_user_id: str,
@@ -119,7 +117,7 @@ class EventStreamHandler:
 
             events.extend(to_add)
 
-            chunks = await self._event_serializer.serialize_events(
+            chunks = self._event_serializer.serialize_events(
                 events,
                 time_now,
                 as_client_event=as_client_event,
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 26b8e3f43c..a37ae0ca09 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -51,7 +51,6 @@ from synapse.logging.context import (
     preserve_fn,
     run_in_background,
 )
-from synapse.logging.utils import log_function
 from synapse.replication.http.federation import (
     ReplicationCleanRoomRestServlet,
     ReplicationStoreRoomOnOutlierMembershipRestServlet,
@@ -556,7 +555,6 @@ class FederationHandler:
 
             run_in_background(self._handle_queued_pdus, room_queue)
 
-    @log_function
     async def do_knock(
         self,
         target_hosts: List[str],
@@ -928,7 +926,6 @@ class FederationHandler:
 
         return event
 
-    @log_function
     async def on_make_knock_request(
         self, origin: str, room_id: str, user_id: str
     ) -> EventBase:
@@ -1039,7 +1036,6 @@ class FederationHandler:
         else:
             return []
 
-    @log_function
     async def on_backfill_request(
         self, origin: str, room_id: str, pdu_list: List[str], limit: int
     ) -> List[EventBase]:
@@ -1056,7 +1052,6 @@ class FederationHandler:
 
         return events
 
-    @log_function
     async def get_persisted_pdu(
         self, origin: str, event_id: str
     ) -> Optional[EventBase]:
@@ -1118,7 +1113,6 @@ class FederationHandler:
 
         return missing_events
 
-    @log_function
     async def exchange_third_party_invite(
         self, sender_user_id: str, target_user_id: str, room_id: str, signed: JsonDict
     ) -> None:
diff --git a/synapse/handlers/federation_event.py b/synapse/handlers/federation_event.py
index 11771f3c9c..3905f60b3a 100644
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -56,7 +56,6 @@ from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.federation.federation_client import InvalidResponseError
 from synapse.logging.context import nested_logging_context, run_in_background
-from synapse.logging.utils import log_function
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.replication.http.devices import ReplicationUserDevicesResyncRestServlet
 from synapse.replication.http.federation import (
@@ -275,7 +274,6 @@ class FederationEventHandler:
 
         await self._process_received_pdu(origin, pdu, state=None)
 
-    @log_function
     async def on_send_membership_event(
         self, origin: str, event: EventBase
     ) -> Tuple[EventBase, EventContext]:
@@ -472,7 +470,6 @@ class FederationEventHandler:
 
             return await self.persist_events_and_notify(room_id, [(event, context)])
 
-    @log_function
     async def backfill(
         self, dest: str, room_id: str, limit: int, extremities: Collection[str]
     ) -> None:
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index 601bab67f9..346a06ff49 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -170,7 +170,7 @@ class InitialSyncHandler:
                 d["inviter"] = event.sender
 
                 invite_event = await self.store.get_event(event.event_id)
-                d["invite"] = await self._event_serializer.serialize_event(
+                d["invite"] = self._event_serializer.serialize_event(
                     invite_event,
                     time_now,
                     as_client_event=as_client_event,
@@ -222,7 +222,7 @@ class InitialSyncHandler:
 
                 d["messages"] = {
                     "chunk": (
-                        await self._event_serializer.serialize_events(
+                        self._event_serializer.serialize_events(
                             messages,
                             time_now=time_now,
                             as_client_event=as_client_event,
@@ -232,7 +232,7 @@ class InitialSyncHandler:
                     "end": await end_token.to_string(self.store),
                 }
 
-                d["state"] = await self._event_serializer.serialize_events(
+                d["state"] = self._event_serializer.serialize_events(
                     current_state.values(),
                     time_now=time_now,
                     as_client_event=as_client_event,
@@ -376,16 +376,14 @@ class InitialSyncHandler:
             "messages": {
                 "chunk": (
                     # Don't bundle aggregations as this is a deprecated API.
-                    await self._event_serializer.serialize_events(messages, time_now)
+                    self._event_serializer.serialize_events(messages, time_now)
                 ),
                 "start": await start_token.to_string(self.store),
                 "end": await end_token.to_string(self.store),
             },
             "state": (
                 # Don't bundle aggregations as this is a deprecated API.
-                await self._event_serializer.serialize_events(
-                    room_state.values(), time_now
-                )
+                self._event_serializer.serialize_events(room_state.values(), time_now)
             ),
             "presence": [],
             "receipts": [],
@@ -404,7 +402,7 @@ class InitialSyncHandler:
         # TODO: These concurrently
         time_now = self.clock.time_msec()
         # Don't bundle aggregations as this is a deprecated API.
-        state = await self._event_serializer.serialize_events(
+        state = self._event_serializer.serialize_events(
             current_state.values(), time_now
         )
 
@@ -480,7 +478,7 @@ class InitialSyncHandler:
             "messages": {
                 "chunk": (
                     # Don't bundle aggregations as this is a deprecated API.
-                    await self._event_serializer.serialize_events(messages, time_now)
+                    self._event_serializer.serialize_events(messages, time_now)
                 ),
                 "start": await start_token.to_string(self.store),
                 "end": await end_token.to_string(self.store),
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 5e3d3886eb..b37250aa38 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -246,7 +246,7 @@ class MessageHandler:
                 room_state = room_state_events[membership_event_id]
 
         now = self.clock.time_msec()
-        events = await self._event_serializer.serialize_events(room_state.values(), now)
+        events = self._event_serializer.serialize_events(room_state.values(), now)
         return events
 
     async def get_joined_members(self, requester: Requester, room_id: str) -> dict:
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index 7469cc55a2..973f262964 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -537,14 +537,16 @@ class PaginationHandler:
                 state_dict = await self.store.get_events(list(state_ids.values()))
                 state = state_dict.values()
 
+        aggregations = await self.store.get_bundled_aggregations(events, user_id)
+
         time_now = self.clock.time_msec()
 
         chunk = {
             "chunk": (
-                await self._event_serializer.serialize_events(
+                self._event_serializer.serialize_events(
                     events,
                     time_now,
-                    bundle_aggregations=True,
+                    bundle_aggregations=aggregations,
                     as_client_event=as_client_event,
                 )
             ),
@@ -553,7 +555,7 @@ class PaginationHandler:
         }
 
         if state:
-            chunk["state"] = await self._event_serializer.serialize_events(
+            chunk["state"] = self._event_serializer.serialize_events(
                 state, time_now, as_client_event=as_client_event
             )
 
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index c781fefb1b..067c43ae47 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -55,7 +55,6 @@ from synapse.api.presence import UserPresenceState
 from synapse.appservice import ApplicationService
 from synapse.events.presence_router import PresenceRouter
 from synapse.logging.context import run_in_background
-from synapse.logging.utils import log_function
 from synapse.metrics import LaterGauge
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.replication.http.presence import (
@@ -1542,7 +1541,6 @@ class PresenceEventSource(EventSource[int, UserPresenceState]):
         self.clock = hs.get_clock()
         self.store = hs.get_datastore()
 
-    @log_function
     async def get_new_events(
         self,
         user: UserID,
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index f08a516a75..68dbae5916 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -979,16 +979,18 @@ class RegistrationHandler:
         if (
             self.hs.config.email.email_enable_notifs
             and self.hs.config.email.email_notif_for_new_users
-            and token
         ):
             # Pull the ID of the access token back out of the db
             # It would really make more sense for this to be passed
             # up when the access token is saved, but that's quite an
             # invasive change I'd rather do separately.
-            user_tuple = await self.store.get_user_by_access_token(token)
-            # The token better still exist.
-            assert user_tuple
-            token_id = user_tuple.token_id
+            if token:
+                user_tuple = await self.store.get_user_by_access_token(token)
+                # The token better still exist.
+                assert user_tuple
+                token_id = user_tuple.token_id
+            else:
+                token_id = None
 
             await self.pusher_pool.add_pusher(
                 user_id=user_id,
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index b9c1cbffa5..f963078e59 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -393,7 +393,9 @@ class RoomCreationHandler:
         user_id = requester.user.to_string()
 
         if not await self.spam_checker.user_may_create_room(user_id):
-            raise SynapseError(403, "You are not permitted to create rooms")
+            raise SynapseError(
+                403, "You are not permitted to create rooms", Codes.FORBIDDEN
+            )
 
         creation_content: JsonDict = {
             "room_version": new_room_version.identifier,
@@ -685,7 +687,9 @@ class RoomCreationHandler:
                 invite_3pid_list,
             )
         ):
-            raise SynapseError(403, "You are not permitted to create rooms")
+            raise SynapseError(
+                403, "You are not permitted to create rooms", Codes.FORBIDDEN
+            )
 
         if ratelimit:
             await self.request_ratelimiter.ratelimit(requester)
@@ -1177,6 +1181,22 @@ class RoomContextHandler:
         # `filtered` rather than the event we retrieved from the datastore.
         results["event"] = filtered[0]
 
+        # Fetch the aggregations.
+        aggregations = await self.store.get_bundled_aggregations(
+            [results["event"]], user.to_string()
+        )
+        aggregations.update(
+            await self.store.get_bundled_aggregations(
+                results["events_before"], user.to_string()
+            )
+        )
+        aggregations.update(
+            await self.store.get_bundled_aggregations(
+                results["events_after"], user.to_string()
+            )
+        )
+        results["aggregations"] = aggregations
+
         if results["events_after"]:
             last_event_id = results["events_after"][-1].event_id
         else:
diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py
index b2cfe537df..7c60cb0bdd 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -153,6 +153,9 @@ class RoomSummaryHandler:
         rooms_result: List[JsonDict] = []
         events_result: List[JsonDict] = []
 
+        if max_rooms_per_space is None or max_rooms_per_space > MAX_ROOMS_PER_SPACE:
+            max_rooms_per_space = MAX_ROOMS_PER_SPACE
+
         while room_queue and len(rooms_result) < MAX_ROOMS:
             queue_entry = room_queue.popleft()
             room_id = queue_entry.room_id
@@ -167,7 +170,7 @@ class RoomSummaryHandler:
             # The client-specified max_rooms_per_space limit doesn't apply to the
             # room_id specified in the request, so we ignore it if this is the
             # first room we are processing.
-            max_children = max_rooms_per_space if processed_rooms else None
+            max_children = max_rooms_per_space if processed_rooms else MAX_ROOMS
 
             if is_in_room:
                 room_entry = await self._summarize_local_room(
@@ -209,7 +212,7 @@ class RoomSummaryHandler:
                         # Before returning to the client, remove the allowed_room_ids
                         # and allowed_spaces keys.
                         room.pop("allowed_room_ids", None)
-                        room.pop("allowed_spaces", None)
+                        room.pop("allowed_spaces", None)  # historical
 
                         rooms_result.append(room)
                         events.extend(room_entry.children_state_events)
@@ -395,7 +398,7 @@ class RoomSummaryHandler:
                     None,
                     room_id,
                     suggested_only,
-                    # TODO Handle max children.
+                    # Do not limit the maximum children.
                     max_children=None,
                 )
 
@@ -525,6 +528,10 @@ class RoomSummaryHandler:
         rooms_result: List[JsonDict] = []
         events_result: List[JsonDict] = []
 
+        # Set a limit on the number of rooms to return.
+        if max_rooms_per_space is None or max_rooms_per_space > MAX_ROOMS_PER_SPACE:
+            max_rooms_per_space = MAX_ROOMS_PER_SPACE
+
         while room_queue and len(rooms_result) < MAX_ROOMS:
             room_id = room_queue.popleft()
             if room_id in processed_rooms:
@@ -583,7 +590,9 @@ class RoomSummaryHandler:
 
         # Iterate through each child and potentially add it, but not its children,
         # to the response.
-        for child_room in root_room_entry.children_state_events:
+        for child_room in itertools.islice(
+            root_room_entry.children_state_events, MAX_ROOMS_PER_SPACE
+        ):
             room_id = child_room.get("state_key")
             assert isinstance(room_id, str)
             # If the room is unknown, skip it.
@@ -633,8 +642,8 @@ class RoomSummaryHandler:
             suggested_only: True if only suggested children should be returned.
                 Otherwise, all children are returned.
             max_children:
-                The maximum number of children rooms to include. This is capped
-                to a server-set limit.
+                The maximum number of children rooms to include. A value of None
+                means no limit.
 
         Returns:
             A room entry if the room should be returned. None, otherwise.
@@ -656,8 +665,13 @@ class RoomSummaryHandler:
             # we only care about suggested children
             child_events = filter(_is_suggested_child_event, child_events)
 
-        if max_children is None or max_children > MAX_ROOMS_PER_SPACE:
-            max_children = MAX_ROOMS_PER_SPACE
+        # TODO max_children is legacy code for the /spaces endpoint.
+        if max_children is not None:
+            child_iter: Iterable[EventBase] = itertools.islice(
+                child_events, max_children
+            )
+        else:
+            child_iter = child_events
 
         stripped_events: List[JsonDict] = [
             {
@@ -668,7 +682,7 @@ class RoomSummaryHandler:
                 "sender": e.sender,
                 "origin_server_ts": e.origin_server_ts,
             }
-            for e in itertools.islice(child_events, max_children)
+            for e in child_iter
         ]
         return _RoomEntry(room_id, room_entry, stripped_events)
 
@@ -988,12 +1002,14 @@ class RoomSummaryHandler:
             "canonical_alias": stats["canonical_alias"],
             "num_joined_members": stats["joined_members"],
             "avatar_url": stats["avatar"],
+            # plural join_rules is a documentation error but kept for historical
+            # purposes. Should match /publicRooms.
             "join_rules": stats["join_rules"],
+            "join_rule": stats["join_rules"],
             "world_readable": (
                 stats["history_visibility"] == HistoryVisibility.WORLD_READABLE
             ),
             "guest_can_join": stats["guest_access"] == "can_join",
-            "creation_ts": create_event.origin_server_ts,
             "room_type": create_event.content.get(EventContentFields.ROOM_TYPE),
         }
 
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index ab7eaab2fb..0b153a6822 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -420,10 +420,10 @@ class SearchHandler:
         time_now = self.clock.time_msec()
 
         for context in contexts.values():
-            context["events_before"] = await self._event_serializer.serialize_events(
+            context["events_before"] = self._event_serializer.serialize_events(
                 context["events_before"], time_now
             )
-            context["events_after"] = await self._event_serializer.serialize_events(
+            context["events_after"] = self._event_serializer.serialize_events(
                 context["events_after"], time_now
             )
 
@@ -441,9 +441,7 @@ class SearchHandler:
             results.append(
                 {
                     "rank": rank_map[e.event_id],
-                    "result": (
-                        await self._event_serializer.serialize_event(e, time_now)
-                    ),
+                    "result": self._event_serializer.serialize_event(e, time_now),
                     "context": contexts.get(e.event_id, {}),
                 }
             )
@@ -457,7 +455,7 @@ class SearchHandler:
         if state_results:
             s = {}
             for room_id, state_events in state_results.items():
-                s[room_id] = await self._event_serializer.serialize_events(
+                s[room_id] = self._event_serializer.serialize_events(
                     state_events, time_now
                 )
 
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 65c27bc64a..0bb8b0929e 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -126,45 +126,45 @@ class SsoIdentityProvider(Protocol):
         raise NotImplementedError()
 
 
-@attr.s
+@attr.s(auto_attribs=True)
 class UserAttributes:
     # the localpart of the mxid that the mapper has assigned to the user.
     # if `None`, the mapper has not picked a userid, and the user should be prompted to
     # enter one.
-    localpart = attr.ib(type=Optional[str])
-    display_name = attr.ib(type=Optional[str], default=None)
-    emails = attr.ib(type=Collection[str], default=attr.Factory(list))
+    localpart: Optional[str]
+    display_name: Optional[str] = None
+    emails: Collection[str] = attr.Factory(list)
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class UsernameMappingSession:
     """Data we track about SSO sessions"""
 
     # A unique identifier for this SSO provider, e.g.  "oidc" or "saml".
-    auth_provider_id = attr.ib(type=str)
+    auth_provider_id: str
 
     # user ID on the IdP server
-    remote_user_id = attr.ib(type=str)
+    remote_user_id: str
 
     # attributes returned by the ID mapper
-    display_name = attr.ib(type=Optional[str])
-    emails = attr.ib(type=Collection[str])
+    display_name: Optional[str]
+    emails: Collection[str]
 
     # An optional dictionary of extra attributes to be provided to the client in the
     # login response.
-    extra_login_attributes = attr.ib(type=Optional[JsonDict])
+    extra_login_attributes: Optional[JsonDict]
 
     # where to redirect the client back to
-    client_redirect_url = attr.ib(type=str)
+    client_redirect_url: str
 
     # expiry time for the session, in milliseconds
-    expiry_time_ms = attr.ib(type=int)
+    expiry_time_ms: int
 
     # choices made by the user
-    chosen_localpart = attr.ib(type=Optional[str], default=None)
-    use_display_name = attr.ib(type=bool, default=True)
-    emails_to_use = attr.ib(type=Collection[str], default=())
-    terms_accepted_version = attr.ib(type=Optional[str], default=None)
+    chosen_localpart: Optional[str] = None
+    use_display_name: bool = True
+    emails_to_use: Collection[str] = ()
+    terms_accepted_version: Optional[str] = None
 
 
 # the HTTP cookie used to track the mapping session id
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 7baf3f199c..ffc6b748e8 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -60,10 +60,6 @@ if TYPE_CHECKING:
 
 logger = logging.getLogger(__name__)
 
-# Debug logger for https://github.com/matrix-org/synapse/issues/4422
-issue4422_logger = logging.getLogger("synapse.handler.sync.4422_debug")
-
-
 # Counts the number of times we returned a non-empty sync. `type` is one of
 # "initial_sync", "full_state_sync" or "incremental_sync", `lazy_loaded` is
 # "true" or "false" depending on if the request asked for lazy loaded members or
@@ -102,6 +98,9 @@ class TimelineBatch:
     prev_batch: StreamToken
     events: List[EventBase]
     limited: bool
+    # A mapping of event ID to the bundled aggregations for the above events.
+    # This is only calculated if limited is true.
+    bundled_aggregations: Optional[Dict[str, Dict[str, Any]]] = None
 
     def __bool__(self) -> bool:
         """Make the result appear empty if there are no updates. This is used
@@ -634,10 +633,19 @@ class SyncHandler:
 
             prev_batch_token = now_token.copy_and_replace("room_key", room_key)
 
+        # Don't bother to bundle aggregations if the timeline is unlimited,
+        # as clients will have all the necessary information.
+        bundled_aggregations = None
+        if limited or newly_joined_room:
+            bundled_aggregations = await self.store.get_bundled_aggregations(
+                recents, sync_config.user.to_string()
+            )
+
         return TimelineBatch(
             events=recents,
             prev_batch=prev_batch_token,
             limited=limited or newly_joined_room,
+            bundled_aggregations=bundled_aggregations,
         )
 
     async def get_state_after_event(
@@ -1161,13 +1169,8 @@ class SyncHandler:
 
         num_events = 0
 
-        # debug for https://github.com/matrix-org/synapse/issues/4422
+        # debug for https://github.com/matrix-org/synapse/issues/9424
         for joined_room in sync_result_builder.joined:
-            room_id = joined_room.room_id
-            if room_id in newly_joined_rooms:
-                issue4422_logger.debug(
-                    "Sync result for newly joined room %s: %r", room_id, joined_room
-                )
             num_events += len(joined_room.timeline.events)
 
         log_kv(
@@ -1740,18 +1743,6 @@ class SyncHandler:
                         old_mem_ev_id, allow_none=True
                     )
 
-                # debug for #4422
-                if has_join:
-                    prev_membership = None
-                    if old_mem_ev:
-                        prev_membership = old_mem_ev.membership
-                    issue4422_logger.debug(
-                        "Previous membership for room %s with join: %s (event %s)",
-                        room_id,
-                        prev_membership,
-                        old_mem_ev_id,
-                    )
-
                 if not old_mem_ev or old_mem_ev.membership != Membership.JOIN:
                     newly_joined_rooms.append(room_id)
 
@@ -1893,13 +1884,6 @@ class SyncHandler:
                     upto_token=since_token,
                 )
 
-            if newly_joined:
-                # debugging for https://github.com/matrix-org/synapse/issues/4422
-                issue4422_logger.debug(
-                    "RoomSyncResultBuilder events for newly joined room %s: %r",
-                    room_id,
-                    entry.events,
-                )
             room_entries.append(entry)
 
         return _RoomChanges(
@@ -2077,14 +2061,6 @@ class SyncHandler:
             # `_load_filtered_recents` can't find any events the user should see
             # (e.g. due to having ignored the sender of the last 50 events).
 
-            if newly_joined:
-                # debug for https://github.com/matrix-org/synapse/issues/4422
-                issue4422_logger.debug(
-                    "Timeline events after filtering in newly-joined room %s: %r",
-                    room_id,
-                    batch,
-                )
-
             # When we join the room (or the client requests full_state), we should
             # send down any existing tags. Usually the user won't have tags in a
             # newly joined room, unless either a) they've joined before or b) the
diff --git a/synapse/http/connectproxyclient.py b/synapse/http/connectproxyclient.py
index fbafffd69b..203e995bb7 100644
--- a/synapse/http/connectproxyclient.py
+++ b/synapse/http/connectproxyclient.py
@@ -32,9 +32,9 @@ class ProxyConnectError(ConnectError):
     pass
 
 
-@attr.s
+@attr.s(auto_attribs=True)
 class ProxyCredentials:
-    username_password = attr.ib(type=bytes)
+    username_password: bytes
 
     def as_proxy_authorization_value(self) -> bytes:
         """
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index deedde0b5b..2e668363b2 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -123,37 +123,37 @@ class ByteParser(ByteWriteable, Generic[T], abc.ABC):
         pass
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class MatrixFederationRequest:
-    method = attr.ib(type=str)
+    method: str
     """HTTP method
     """
 
-    path = attr.ib(type=str)
+    path: str
     """HTTP path
     """
 
-    destination = attr.ib(type=str)
+    destination: str
     """The remote server to send the HTTP request to.
     """
 
-    json = attr.ib(default=None, type=Optional[JsonDict])
+    json: Optional[JsonDict] = None
     """JSON to send in the body.
     """
 
-    json_callback = attr.ib(default=None, type=Optional[Callable[[], JsonDict]])
+    json_callback: Optional[Callable[[], JsonDict]] = None
     """A callback to generate the JSON.
     """
 
-    query = attr.ib(default=None, type=Optional[dict])
+    query: Optional[dict] = None
     """Query arguments.
     """
 
-    txn_id = attr.ib(default=None, type=Optional[str])
+    txn_id: Optional[str] = None
     """Unique ID for this request (for logging)
     """
 
-    uri = attr.ib(init=False, type=bytes)
+    uri: bytes = attr.ib(init=False)
     """The URI of this request
     """
 
diff --git a/synapse/http/site.py b/synapse/http/site.py
index 80f7a2ff58..c180a1d323 100644
--- a/synapse/http/site.py
+++ b/synapse/http/site.py
@@ -534,9 +534,9 @@ class XForwardedForRequest(SynapseRequest):
 
 
 @implementer(IAddress)
-@attr.s(frozen=True, slots=True)
+@attr.s(frozen=True, slots=True, auto_attribs=True)
 class _XForwardedForAddress:
-    host = attr.ib(type=str)
+    host: str
 
 
 class SynapseSite(Site):
diff --git a/synapse/logging/_remote.py b/synapse/logging/_remote.py
index 8202d0494d..475756f1db 100644
--- a/synapse/logging/_remote.py
+++ b/synapse/logging/_remote.py
@@ -39,7 +39,7 @@ from twisted.python.failure import Failure
 logger = logging.getLogger(__name__)
 
 
-@attr.s
+@attr.s(slots=True, auto_attribs=True)
 @implementer(IPushProducer)
 class LogProducer:
     """
@@ -54,10 +54,10 @@ class LogProducer:
 
     # This is essentially ITCPTransport, but that is missing certain fields
     # (connected and registerProducer) which are part of the implementation.
-    transport = attr.ib(type=Connection)
-    _format = attr.ib(type=Callable[[logging.LogRecord], str])
-    _buffer = attr.ib(type=deque)
-    _paused = attr.ib(default=False, type=bool, init=False)
+    transport: Connection
+    _format: Callable[[logging.LogRecord], str]
+    _buffer: Deque[logging.LogRecord]
+    _paused: bool = attr.ib(default=False, init=False)
 
     def pauseProducing(self):
         self._paused = True
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index d4ee893376..c31c2960ad 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -193,7 +193,7 @@ class ContextResourceUsage:
         return res
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class ContextRequest:
     """
     A bundle of attributes from the SynapseRequest object.
@@ -205,15 +205,15 @@ class ContextRequest:
       their children.
     """
 
-    request_id = attr.ib(type=str)
-    ip_address = attr.ib(type=str)
-    site_tag = attr.ib(type=str)
-    requester = attr.ib(type=Optional[str])
-    authenticated_entity = attr.ib(type=Optional[str])
-    method = attr.ib(type=str)
-    url = attr.ib(type=str)
-    protocol = attr.ib(type=str)
-    user_agent = attr.ib(type=str)
+    request_id: str
+    ip_address: str
+    site_tag: str
+    requester: Optional[str]
+    authenticated_entity: Optional[str]
+    method: str
+    url: str
+    protocol: str
+    user_agent: str
 
 
 LoggingContextOrSentinel = Union["LoggingContext", "_Sentinel"]
diff --git a/synapse/logging/opentracing.py b/synapse/logging/opentracing.py
index 622445e9f4..5672d60de3 100644
--- a/synapse/logging/opentracing.py
+++ b/synapse/logging/opentracing.py
@@ -251,7 +251,7 @@ try:
     class _WrappedRustReporter(BaseReporter):
         """Wrap the reporter to ensure `report_span` never throws."""
 
-        _reporter = attr.ib(type=Reporter, default=attr.Factory(Reporter))
+        _reporter: Reporter = attr.Factory(Reporter)
 
         def set_process(self, *args, **kwargs):
             return self._reporter.set_process(*args, **kwargs)
diff --git a/synapse/logging/utils.py b/synapse/logging/utils.py
deleted file mode 100644
index 4a01b902c2..0000000000
--- a/synapse/logging/utils.py
+++ /dev/null
@@ -1,76 +0,0 @@
-# Copyright 2014-2016 OpenMarket Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-
-import logging
-from functools import wraps
-from inspect import getcallargs
-from typing import Callable, TypeVar, cast
-
-_TIME_FUNC_ID = 0
-
-
-def _log_debug_as_f(f, msg, msg_args):
-    name = f.__module__
-    logger = logging.getLogger(name)
-
-    if logger.isEnabledFor(logging.DEBUG):
-        lineno = f.__code__.co_firstlineno
-        pathname = f.__code__.co_filename
-
-        record = logger.makeRecord(
-            name=name,
-            level=logging.DEBUG,
-            fn=pathname,
-            lno=lineno,
-            msg=msg,
-            args=msg_args,
-            exc_info=None,
-        )
-
-        logger.handle(record)
-
-
-F = TypeVar("F", bound=Callable)
-
-
-def log_function(f: F) -> F:
-    """Function decorator that logs every call to that function."""
-    func_name = f.__name__
-
-    @wraps(f)
-    def wrapped(*args, **kwargs):
-        name = f.__module__
-        logger = logging.getLogger(name)
-        level = logging.DEBUG
-
-        if logger.isEnabledFor(level):
-            bound_args = getcallargs(f, *args, **kwargs)
-
-            def format(value):
-                r = str(value)
-                if len(r) > 50:
-                    r = r[:50] + "..."
-                return r
-
-            func_args = ["%s=%s" % (k, format(v)) for k, v in bound_args.items()]
-
-            msg_args = {"func_name": func_name, "args": ", ".join(func_args)}
-
-            _log_debug_as_f(f, "Invoked '%(func_name)s' with args: %(args)s", msg_args)
-
-        return f(*args, **kwargs)
-
-    wrapped.__name__ = func_name
-    return cast(F, wrapped)
diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index ceef57ad88..9e6c1b2f3b 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -12,16 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import functools
-import gc
 import itertools
 import logging
 import os
 import platform
 import threading
-import time
 from typing import (
-    Any,
     Callable,
     Dict,
     Generic,
@@ -34,35 +30,31 @@ from typing import (
     Type,
     TypeVar,
     Union,
-    cast,
 )
 
 import attr
 from prometheus_client import CollectorRegistry, Counter, Gauge, Histogram, Metric
 from prometheus_client.core import (
     REGISTRY,
-    CounterMetricFamily,
     GaugeHistogramMetricFamily,
     GaugeMetricFamily,
 )
 
-from twisted.internet import reactor
-from twisted.internet.base import ReactorBase
 from twisted.python.threadpool import ThreadPool
 
-import synapse
+import synapse.metrics._reactor_metrics
 from synapse.metrics._exposition import (
     MetricsResource,
     generate_latest,
     start_http_server,
 )
+from synapse.metrics._gc import MIN_TIME_BETWEEN_GCS, install_gc_manager
 from synapse.util.versionstring import get_version_string
 
 logger = logging.getLogger(__name__)
 
 METRICS_PREFIX = "/_synapse/metrics"
 
-running_on_pypy = platform.python_implementation() == "PyPy"
 all_gauges: "Dict[str, Union[LaterGauge, InFlightGauge]]" = {}
 
 HAVE_PROC_SELF_STAT = os.path.exists("/proc/self/stat")
@@ -76,19 +68,17 @@ class RegistryProxy:
                 yield metric
 
 
-@attr.s(slots=True, hash=True)
+@attr.s(slots=True, hash=True, auto_attribs=True)
 class LaterGauge:
 
-    name = attr.ib(type=str)
-    desc = attr.ib(type=str)
-    labels = attr.ib(hash=False, type=Optional[Iterable[str]])
+    name: str
+    desc: str
+    labels: Optional[Iterable[str]] = attr.ib(hash=False)
     # callback: should either return a value (if there are no labels for this metric),
     # or dict mapping from a label tuple to a value
-    caller = attr.ib(
-        type=Callable[
-            [], Union[Mapping[Tuple[str, ...], Union[int, float]], Union[int, float]]
-        ]
-    )
+    caller: Callable[
+        [], Union[Mapping[Tuple[str, ...], Union[int, float]], Union[int, float]]
+    ]
 
     def collect(self) -> Iterable[Metric]:
 
@@ -157,7 +147,9 @@ class InFlightGauge(Generic[MetricsEntry]):
         # Create a class which have the sub_metrics values as attributes, which
         # default to 0 on initialization. Used to pass to registered callbacks.
         self._metrics_class: Type[MetricsEntry] = attr.make_class(
-            "_MetricsEntry", attrs={x: attr.ib(0) for x in sub_metrics}, slots=True
+            "_MetricsEntry",
+            attrs={x: attr.ib(default=0) for x in sub_metrics},
+            slots=True,
         )
 
         # Counts number of in flight blocks for a given set of label values
@@ -369,136 +361,6 @@ class CPUMetrics:
 
 REGISTRY.register(CPUMetrics())
 
-#
-# Python GC metrics
-#
-
-gc_unreachable = Gauge("python_gc_unreachable_total", "Unreachable GC objects", ["gen"])
-gc_time = Histogram(
-    "python_gc_time",
-    "Time taken to GC (sec)",
-    ["gen"],
-    buckets=[
-        0.0025,
-        0.005,
-        0.01,
-        0.025,
-        0.05,
-        0.10,
-        0.25,
-        0.50,
-        1.00,
-        2.50,
-        5.00,
-        7.50,
-        15.00,
-        30.00,
-        45.00,
-        60.00,
-    ],
-)
-
-
-class GCCounts:
-    def collect(self) -> Iterable[Metric]:
-        cm = GaugeMetricFamily("python_gc_counts", "GC object counts", labels=["gen"])
-        for n, m in enumerate(gc.get_count()):
-            cm.add_metric([str(n)], m)
-
-        yield cm
-
-
-if not running_on_pypy:
-    REGISTRY.register(GCCounts())
-
-
-#
-# PyPy GC / memory metrics
-#
-
-
-class PyPyGCStats:
-    def collect(self) -> Iterable[Metric]:
-
-        # @stats is a pretty-printer object with __str__() returning a nice table,
-        # plus some fields that contain data from that table.
-        # unfortunately, fields are pretty-printed themselves (i. e. '4.5MB').
-        stats = gc.get_stats(memory_pressure=False)  # type: ignore
-        # @s contains same fields as @stats, but as actual integers.
-        s = stats._s  # type: ignore
-
-        # also note that field naming is completely braindead
-        # and only vaguely correlates with the pretty-printed table.
-        # >>>> gc.get_stats(False)
-        # Total memory consumed:
-        #     GC used:            8.7MB (peak: 39.0MB)        # s.total_gc_memory, s.peak_memory
-        #        in arenas:            3.0MB                  # s.total_arena_memory
-        #        rawmalloced:          1.7MB                  # s.total_rawmalloced_memory
-        #        nursery:              4.0MB                  # s.nursery_size
-        #     raw assembler used: 31.0kB                      # s.jit_backend_used
-        #     -----------------------------
-        #     Total:              8.8MB                       # stats.memory_used_sum
-        #
-        #     Total memory allocated:
-        #     GC allocated:            38.7MB (peak: 41.1MB)  # s.total_allocated_memory, s.peak_allocated_memory
-        #        in arenas:            30.9MB                 # s.peak_arena_memory
-        #        rawmalloced:          4.1MB                  # s.peak_rawmalloced_memory
-        #        nursery:              4.0MB                  # s.nursery_size
-        #     raw assembler allocated: 1.0MB                  # s.jit_backend_allocated
-        #     -----------------------------
-        #     Total:                   39.7MB                 # stats.memory_allocated_sum
-        #
-        #     Total time spent in GC:  0.073                  # s.total_gc_time
-
-        pypy_gc_time = CounterMetricFamily(
-            "pypy_gc_time_seconds_total",
-            "Total time spent in PyPy GC",
-            labels=[],
-        )
-        pypy_gc_time.add_metric([], s.total_gc_time / 1000)
-        yield pypy_gc_time
-
-        pypy_mem = GaugeMetricFamily(
-            "pypy_memory_bytes",
-            "Memory tracked by PyPy allocator",
-            labels=["state", "class", "kind"],
-        )
-        # memory used by JIT assembler
-        pypy_mem.add_metric(["used", "", "jit"], s.jit_backend_used)
-        pypy_mem.add_metric(["allocated", "", "jit"], s.jit_backend_allocated)
-        # memory used by GCed objects
-        pypy_mem.add_metric(["used", "", "arenas"], s.total_arena_memory)
-        pypy_mem.add_metric(["allocated", "", "arenas"], s.peak_arena_memory)
-        pypy_mem.add_metric(["used", "", "rawmalloced"], s.total_rawmalloced_memory)
-        pypy_mem.add_metric(["allocated", "", "rawmalloced"], s.peak_rawmalloced_memory)
-        pypy_mem.add_metric(["used", "", "nursery"], s.nursery_size)
-        pypy_mem.add_metric(["allocated", "", "nursery"], s.nursery_size)
-        # totals
-        pypy_mem.add_metric(["used", "totals", "gc"], s.total_gc_memory)
-        pypy_mem.add_metric(["allocated", "totals", "gc"], s.total_allocated_memory)
-        pypy_mem.add_metric(["used", "totals", "gc_peak"], s.peak_memory)
-        pypy_mem.add_metric(["allocated", "totals", "gc_peak"], s.peak_allocated_memory)
-        yield pypy_mem
-
-
-if running_on_pypy:
-    REGISTRY.register(PyPyGCStats())
-
-
-#
-# Twisted reactor metrics
-#
-
-tick_time = Histogram(
-    "python_twisted_reactor_tick_time",
-    "Tick time of the Twisted reactor (sec)",
-    buckets=[0.001, 0.002, 0.005, 0.01, 0.025, 0.05, 0.1, 0.2, 0.5, 1, 2, 5],
-)
-pending_calls_metric = Histogram(
-    "python_twisted_reactor_pending_calls",
-    "Pending calls",
-    buckets=[1, 2, 5, 10, 25, 50, 100, 250, 500, 1000],
-)
 
 #
 # Federation Metrics
@@ -551,8 +413,6 @@ build_info.labels(
     " ".join([platform.system(), platform.release()]),
 ).set(1)
 
-last_ticked = time.time()
-
 # 3PID send info
 threepid_send_requests = Histogram(
     "synapse_threepid_send_requests_with_tries",
@@ -600,116 +460,6 @@ def register_threadpool(name: str, threadpool: ThreadPool) -> None:
     )
 
 
-class ReactorLastSeenMetric:
-    def collect(self) -> Iterable[Metric]:
-        cm = GaugeMetricFamily(
-            "python_twisted_reactor_last_seen",
-            "Seconds since the Twisted reactor was last seen",
-        )
-        cm.add_metric([], time.time() - last_ticked)
-        yield cm
-
-
-REGISTRY.register(ReactorLastSeenMetric())
-
-# The minimum time in seconds between GCs for each generation, regardless of the current GC
-# thresholds and counts.
-MIN_TIME_BETWEEN_GCS = (1.0, 10.0, 30.0)
-
-# The time (in seconds since the epoch) of the last time we did a GC for each generation.
-_last_gc = [0.0, 0.0, 0.0]
-
-
-F = TypeVar("F", bound=Callable[..., Any])
-
-
-def runUntilCurrentTimer(reactor: ReactorBase, func: F) -> F:
-    @functools.wraps(func)
-    def f(*args: Any, **kwargs: Any) -> Any:
-        now = reactor.seconds()
-        num_pending = 0
-
-        # _newTimedCalls is one long list of *all* pending calls. Below loop
-        # is based off of impl of reactor.runUntilCurrent
-        for delayed_call in reactor._newTimedCalls:
-            if delayed_call.time > now:
-                break
-
-            if delayed_call.delayed_time > 0:
-                continue
-
-            num_pending += 1
-
-        num_pending += len(reactor.threadCallQueue)
-        start = time.time()
-        ret = func(*args, **kwargs)
-        end = time.time()
-
-        # record the amount of wallclock time spent running pending calls.
-        # This is a proxy for the actual amount of time between reactor polls,
-        # since about 25% of time is actually spent running things triggered by
-        # I/O events, but that is harder to capture without rewriting half the
-        # reactor.
-        tick_time.observe(end - start)
-        pending_calls_metric.observe(num_pending)
-
-        # Update the time we last ticked, for the metric to test whether
-        # Synapse's reactor has frozen
-        global last_ticked
-        last_ticked = end
-
-        if running_on_pypy:
-            return ret
-
-        # Check if we need to do a manual GC (since its been disabled), and do
-        # one if necessary. Note we go in reverse order as e.g. a gen 1 GC may
-        # promote an object into gen 2, and we don't want to handle the same
-        # object multiple times.
-        threshold = gc.get_threshold()
-        counts = gc.get_count()
-        for i in (2, 1, 0):
-            # We check if we need to do one based on a straightforward
-            # comparison between the threshold and count. We also do an extra
-            # check to make sure that we don't a GC too often.
-            if threshold[i] < counts[i] and MIN_TIME_BETWEEN_GCS[i] < end - _last_gc[i]:
-                if i == 0:
-                    logger.debug("Collecting gc %d", i)
-                else:
-                    logger.info("Collecting gc %d", i)
-
-                start = time.time()
-                unreachable = gc.collect(i)
-                end = time.time()
-
-                _last_gc[i] = end
-
-                gc_time.labels(i).observe(end - start)
-                gc_unreachable.labels(i).set(unreachable)
-
-        return ret
-
-    return cast(F, f)
-
-
-try:
-    # Ensure the reactor has all the attributes we expect
-    reactor.seconds  # type: ignore
-    reactor.runUntilCurrent  # type: ignore
-    reactor._newTimedCalls  # type: ignore
-    reactor.threadCallQueue  # type: ignore
-
-    # runUntilCurrent is called when we have pending calls. It is called once
-    # per iteratation after fd polling.
-    reactor.runUntilCurrent = runUntilCurrentTimer(reactor, reactor.runUntilCurrent)  # type: ignore
-
-    # We manually run the GC each reactor tick so that we can get some metrics
-    # about time spent doing GC,
-    if not running_on_pypy:
-        gc.disable()
-except AttributeError:
-    pass
-
-
 __all__ = [
     "MetricsResource",
     "generate_latest",
@@ -717,4 +467,6 @@ __all__ = [
     "LaterGauge",
     "InFlightGauge",
     "GaugeBucketCollector",
+    "MIN_TIME_BETWEEN_GCS",
+    "install_gc_manager",
 ]
diff --git a/synapse/metrics/_gc.py b/synapse/metrics/_gc.py
new file mode 100644
index 0000000000..2bc909efa0
--- /dev/null
+++ b/synapse/metrics/_gc.py
@@ -0,0 +1,203 @@
+# Copyright 2015-2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import gc
+import logging
+import platform
+import time
+from typing import Iterable
+
+from prometheus_client.core import (
+    REGISTRY,
+    CounterMetricFamily,
+    Gauge,
+    GaugeMetricFamily,
+    Histogram,
+    Metric,
+)
+
+from twisted.internet import task
+
+"""Prometheus metrics for garbage collection"""
+
+
+logger = logging.getLogger(__name__)
+
+# The minimum time in seconds between GCs for each generation, regardless of the current GC
+# thresholds and counts.
+MIN_TIME_BETWEEN_GCS = (1.0, 10.0, 30.0)
+
+running_on_pypy = platform.python_implementation() == "PyPy"
+
+#
+# Python GC metrics
+#
+
+gc_unreachable = Gauge("python_gc_unreachable_total", "Unreachable GC objects", ["gen"])
+gc_time = Histogram(
+    "python_gc_time",
+    "Time taken to GC (sec)",
+    ["gen"],
+    buckets=[
+        0.0025,
+        0.005,
+        0.01,
+        0.025,
+        0.05,
+        0.10,
+        0.25,
+        0.50,
+        1.00,
+        2.50,
+        5.00,
+        7.50,
+        15.00,
+        30.00,
+        45.00,
+        60.00,
+    ],
+)
+
+
+class GCCounts:
+    def collect(self) -> Iterable[Metric]:
+        cm = GaugeMetricFamily("python_gc_counts", "GC object counts", labels=["gen"])
+        for n, m in enumerate(gc.get_count()):
+            cm.add_metric([str(n)], m)
+
+        yield cm
+
+
+def install_gc_manager() -> None:
+    """Disable automatic GC, and replace it with a task that runs every 100ms
+
+    This means that (a) we can limit how often GC runs; (b) we can get some metrics
+    about GC activity.
+
+    It does nothing on PyPy.
+    """
+
+    if running_on_pypy:
+        return
+
+    REGISTRY.register(GCCounts())
+
+    gc.disable()
+
+    # The time (in seconds since the epoch) of the last time we did a GC for each generation.
+    _last_gc = [0.0, 0.0, 0.0]
+
+    def _maybe_gc() -> None:
+        # Check if we need to do a manual GC (since its been disabled), and do
+        # one if necessary. Note we go in reverse order as e.g. a gen 1 GC may
+        # promote an object into gen 2, and we don't want to handle the same
+        # object multiple times.
+        threshold = gc.get_threshold()
+        counts = gc.get_count()
+        end = time.time()
+        for i in (2, 1, 0):
+            # We check if we need to do one based on a straightforward
+            # comparison between the threshold and count. We also do an extra
+            # check to make sure that we don't a GC too often.
+            if threshold[i] < counts[i] and MIN_TIME_BETWEEN_GCS[i] < end - _last_gc[i]:
+                if i == 0:
+                    logger.debug("Collecting gc %d", i)
+                else:
+                    logger.info("Collecting gc %d", i)
+
+                start = time.time()
+                unreachable = gc.collect(i)
+                end = time.time()
+
+                _last_gc[i] = end
+
+                gc_time.labels(i).observe(end - start)
+                gc_unreachable.labels(i).set(unreachable)
+
+    gc_task = task.LoopingCall(_maybe_gc)
+    gc_task.start(0.1)
+
+
+#
+# PyPy GC / memory metrics
+#
+
+
+class PyPyGCStats:
+    def collect(self) -> Iterable[Metric]:
+
+        # @stats is a pretty-printer object with __str__() returning a nice table,
+        # plus some fields that contain data from that table.
+        # unfortunately, fields are pretty-printed themselves (i. e. '4.5MB').
+        stats = gc.get_stats(memory_pressure=False)  # type: ignore
+        # @s contains same fields as @stats, but as actual integers.
+        s = stats._s  # type: ignore
+
+        # also note that field naming is completely braindead
+        # and only vaguely correlates with the pretty-printed table.
+        # >>>> gc.get_stats(False)
+        # Total memory consumed:
+        #     GC used:            8.7MB (peak: 39.0MB)        # s.total_gc_memory, s.peak_memory
+        #        in arenas:            3.0MB                  # s.total_arena_memory
+        #        rawmalloced:          1.7MB                  # s.total_rawmalloced_memory
+        #        nursery:              4.0MB                  # s.nursery_size
+        #     raw assembler used: 31.0kB                      # s.jit_backend_used
+        #     -----------------------------
+        #     Total:              8.8MB                       # stats.memory_used_sum
+        #
+        #     Total memory allocated:
+        #     GC allocated:            38.7MB (peak: 41.1MB)  # s.total_allocated_memory, s.peak_allocated_memory
+        #        in arenas:            30.9MB                 # s.peak_arena_memory
+        #        rawmalloced:          4.1MB                  # s.peak_rawmalloced_memory
+        #        nursery:              4.0MB                  # s.nursery_size
+        #     raw assembler allocated: 1.0MB                  # s.jit_backend_allocated
+        #     -----------------------------
+        #     Total:                   39.7MB                 # stats.memory_allocated_sum
+        #
+        #     Total time spent in GC:  0.073                  # s.total_gc_time
+
+        pypy_gc_time = CounterMetricFamily(
+            "pypy_gc_time_seconds_total",
+            "Total time spent in PyPy GC",
+            labels=[],
+        )
+        pypy_gc_time.add_metric([], s.total_gc_time / 1000)
+        yield pypy_gc_time
+
+        pypy_mem = GaugeMetricFamily(
+            "pypy_memory_bytes",
+            "Memory tracked by PyPy allocator",
+            labels=["state", "class", "kind"],
+        )
+        # memory used by JIT assembler
+        pypy_mem.add_metric(["used", "", "jit"], s.jit_backend_used)
+        pypy_mem.add_metric(["allocated", "", "jit"], s.jit_backend_allocated)
+        # memory used by GCed objects
+        pypy_mem.add_metric(["used", "", "arenas"], s.total_arena_memory)
+        pypy_mem.add_metric(["allocated", "", "arenas"], s.peak_arena_memory)
+        pypy_mem.add_metric(["used", "", "rawmalloced"], s.total_rawmalloced_memory)
+        pypy_mem.add_metric(["allocated", "", "rawmalloced"], s.peak_rawmalloced_memory)
+        pypy_mem.add_metric(["used", "", "nursery"], s.nursery_size)
+        pypy_mem.add_metric(["allocated", "", "nursery"], s.nursery_size)
+        # totals
+        pypy_mem.add_metric(["used", "totals", "gc"], s.total_gc_memory)
+        pypy_mem.add_metric(["allocated", "totals", "gc"], s.total_allocated_memory)
+        pypy_mem.add_metric(["used", "totals", "gc_peak"], s.peak_memory)
+        pypy_mem.add_metric(["allocated", "totals", "gc_peak"], s.peak_allocated_memory)
+        yield pypy_mem
+
+
+if running_on_pypy:
+    REGISTRY.register(PyPyGCStats())
diff --git a/synapse/metrics/_reactor_metrics.py b/synapse/metrics/_reactor_metrics.py
new file mode 100644
index 0000000000..ce0688621c
--- /dev/null
+++ b/synapse/metrics/_reactor_metrics.py
@@ -0,0 +1,83 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import select
+import time
+from typing import Any, Iterable, List, Tuple
+
+from prometheus_client import Histogram, Metric
+from prometheus_client.core import REGISTRY, GaugeMetricFamily
+
+from twisted.internet import reactor
+
+#
+# Twisted reactor metrics
+#
+
+tick_time = Histogram(
+    "python_twisted_reactor_tick_time",
+    "Tick time of the Twisted reactor (sec)",
+    buckets=[0.001, 0.002, 0.005, 0.01, 0.025, 0.05, 0.1, 0.2, 0.5, 1, 2, 5],
+)
+
+
+class EpollWrapper:
+    """a wrapper for an epoll object which records the time between polls"""
+
+    def __init__(self, poller: "select.epoll"):
+        self.last_polled = time.time()
+        self._poller = poller
+
+    def poll(self, *args, **kwargs) -> List[Tuple[int, int]]:  # type: ignore[no-untyped-def]
+        # record the time since poll() was last called. This gives a good proxy for
+        # how long it takes to run everything in the reactor - ie, how long anything
+        # waiting for the next tick will have to wait.
+        tick_time.observe(time.time() - self.last_polled)
+
+        ret = self._poller.poll(*args, **kwargs)
+
+        self.last_polled = time.time()
+        return ret
+
+    def __getattr__(self, item: str) -> Any:
+        return getattr(self._poller, item)
+
+
+class ReactorLastSeenMetric:
+    def __init__(self, epoll_wrapper: EpollWrapper):
+        self._epoll_wrapper = epoll_wrapper
+
+    def collect(self) -> Iterable[Metric]:
+        cm = GaugeMetricFamily(
+            "python_twisted_reactor_last_seen",
+            "Seconds since the Twisted reactor was last seen",
+        )
+        cm.add_metric([], time.time() - self._epoll_wrapper.last_polled)
+        yield cm
+
+
+try:
+    # if the reactor has a `_poller` attribute, which is an `epoll` object
+    # (ie, it's an EPollReactor), we wrap the `epoll` with a thing that will
+    # measure the time between ticks
+    from select import epoll
+
+    poller = reactor._poller  # type: ignore[attr-defined]
+except (AttributeError, ImportError):
+    pass
+else:
+    if isinstance(poller, epoll):
+        poller = EpollWrapper(poller)
+        reactor._poller = poller  # type: ignore[attr-defined]
+        REGISTRY.register(ReactorLastSeenMetric(poller))
diff --git a/synapse/notifier.py b/synapse/notifier.py
index bbabdb0587..632b2245ef 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -40,7 +40,6 @@ from synapse.handlers.presence import format_user_presence_state
 from synapse.logging import issue9533_logger
 from synapse.logging.context import PreserveLoggingContext
 from synapse.logging.opentracing import log_kv, start_active_span
-from synapse.logging.utils import log_function
 from synapse.metrics import LaterGauge
 from synapse.streams.config import PaginationConfig
 from synapse.types import (
@@ -193,15 +192,15 @@ class EventStreamResult:
         return bool(self.events)
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class _PendingRoomEventEntry:
-    event_pos = attr.ib(type=PersistedEventPosition)
-    extra_users = attr.ib(type=Collection[UserID])
+    event_pos: PersistedEventPosition
+    extra_users: Collection[UserID]
 
-    room_id = attr.ib(type=str)
-    type = attr.ib(type=str)
-    state_key = attr.ib(type=Optional[str])
-    membership = attr.ib(type=Optional[str])
+    room_id: str
+    type: str
+    state_key: Optional[str]
+    membership: Optional[str]
 
 
 class Notifier:
@@ -686,7 +685,6 @@ class Notifier:
         else:
             return False
 
-    @log_function
     def remove_expired_streams(self) -> None:
         time_now_ms = self.clock.time_msec()
         expired_streams = []
@@ -700,7 +698,6 @@ class Notifier:
         for expired_stream in expired_streams:
             expired_stream.remove(self)
 
-    @log_function
     def _register_with_keys(self, user_stream: _NotifierUserStream):
         self.user_to_user_stream[user_stream.user_id] = user_stream
 
diff --git a/synapse/push/__init__.py b/synapse/push/__init__.py
index 820f6f3f7e..5176a1c186 100644
--- a/synapse/push/__init__.py
+++ b/synapse/push/__init__.py
@@ -23,25 +23,25 @@ if TYPE_CHECKING:
     from synapse.server import HomeServer
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class PusherConfig:
     """Parameters necessary to configure a pusher."""
 
-    id = attr.ib(type=Optional[str])
-    user_name = attr.ib(type=str)
-    access_token = attr.ib(type=Optional[int])
-    profile_tag = attr.ib(type=str)
-    kind = attr.ib(type=str)
-    app_id = attr.ib(type=str)
-    app_display_name = attr.ib(type=str)
-    device_display_name = attr.ib(type=str)
-    pushkey = attr.ib(type=str)
-    ts = attr.ib(type=int)
-    lang = attr.ib(type=Optional[str])
-    data = attr.ib(type=Optional[JsonDict])
-    last_stream_ordering = attr.ib(type=int)
-    last_success = attr.ib(type=Optional[int])
-    failing_since = attr.ib(type=Optional[int])
+    id: Optional[str]
+    user_name: str
+    access_token: Optional[int]
+    profile_tag: str
+    kind: str
+    app_id: str
+    app_display_name: str
+    device_display_name: str
+    pushkey: str
+    ts: int
+    lang: Optional[str]
+    data: Optional[JsonDict]
+    last_stream_ordering: int
+    last_success: Optional[int]
+    failing_since: Optional[int]
 
     def as_dict(self) -> Dict[str, Any]:
         """Information that can be retrieved about a pusher after creation."""
@@ -57,12 +57,12 @@ class PusherConfig:
         }
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class ThrottleParams:
     """Parameters for controlling the rate of sending pushes via email."""
 
-    last_sent_ts = attr.ib(type=int)
-    throttle_ms = attr.ib(type=int)
+    last_sent_ts: int
+    throttle_ms: int
 
 
 class Pusher(metaclass=abc.ABCMeta):
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index 009d8e77b0..bee660893b 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -298,7 +298,7 @@ RulesByUser = Dict[str, List[Rule]]
 StateGroup = Union[object, int]
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class RulesForRoomData:
     """The data stored in the cache by `RulesForRoom`.
 
@@ -307,29 +307,29 @@ class RulesForRoomData:
     """
 
     # event_id -> (user_id, state)
-    member_map = attr.ib(type=MemberMap, factory=dict)
+    member_map: MemberMap = attr.Factory(dict)
     # user_id -> rules
-    rules_by_user = attr.ib(type=RulesByUser, factory=dict)
+    rules_by_user: RulesByUser = attr.Factory(dict)
 
     # The last state group we updated the caches for. If the state_group of
     # a new event comes along, we know that we can just return the cached
     # result.
     # On invalidation of the rules themselves (if the user changes them),
     # we invalidate everything and set state_group to `object()`
-    state_group = attr.ib(type=StateGroup, factory=object)
+    state_group: StateGroup = attr.Factory(object)
 
     # A sequence number to keep track of when we're allowed to update the
     # cache. We bump the sequence number when we invalidate the cache. If
     # the sequence number changes while we're calculating stuff we should
     # not update the cache with it.
-    sequence = attr.ib(type=int, default=0)
+    sequence: int = 0
 
     # A cache of user_ids that we *know* aren't interesting, e.g. user_ids
     # owned by AS's, or remote users, etc. (I.e. users we will never need to
     # calculate push for)
     # These never need to be invalidated as we will never set up push for
     # them.
-    uninteresting_user_set = attr.ib(type=Set[str], factory=set)
+    uninteresting_user_set: Set[str] = attr.Factory(set)
 
 
 class RulesForRoom:
@@ -553,7 +553,7 @@ class RulesForRoom:
             self.data.state_group = state_group
 
 
-@attr.attrs(slots=True, frozen=True)
+@attr.attrs(slots=True, frozen=True, auto_attribs=True)
 class _Invalidation:
     # _Invalidation is passed as an `on_invalidate` callback to bulk_get_push_rules,
     # which means that it it is stored on the bulk_get_push_rules cache entry. In order
@@ -564,8 +564,8 @@ class _Invalidation:
     # attrs provides suitable __hash__ and __eq__ methods, provided we remember to
     # set `frozen=True`.
 
-    cache = attr.ib(type=LruCache)
-    room_id = attr.ib(type=str)
+    cache: LruCache
+    room_id: str
 
     def __call__(self) -> None:
         rules_data = self.cache.get(self.room_id, None, update_metrics=False)
diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index ff904c2b4a..dadfc57413 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -178,7 +178,7 @@ class Mailer:
         await self.send_email(
             email_address,
             self.email_subjects.email_validation
-            % {"server_name": self.hs.config.server.server_name},
+            % {"server_name": self.hs.config.server.server_name, "app": self.app_name},
             template_vars,
         )
 
@@ -209,7 +209,7 @@ class Mailer:
         await self.send_email(
             email_address,
             self.email_subjects.email_validation
-            % {"server_name": self.hs.config.server.server_name},
+            % {"server_name": self.hs.config.server.server_name, "app": self.app_name},
             template_vars,
         )
 
diff --git a/synapse/replication/tcp/streams/events.py b/synapse/replication/tcp/streams/events.py
index a390cfcb74..4f4f1ad453 100644
--- a/synapse/replication/tcp/streams/events.py
+++ b/synapse/replication/tcp/streams/events.py
@@ -50,12 +50,12 @@ data part are:
 """
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class EventsStreamRow:
     """A parsed row from the events replication stream"""
 
-    type = attr.ib()  # str: the TypeId of one of the *EventsStreamRows
-    data = attr.ib()  # BaseEventsStreamRow
+    type: str  # the TypeId of one of the *EventsStreamRows
+    data: "BaseEventsStreamRow"
 
 
 class BaseEventsStreamRow:
@@ -79,28 +79,28 @@ class BaseEventsStreamRow:
         return cls(*data)
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class EventsStreamEventRow(BaseEventsStreamRow):
     TypeId = "ev"
 
-    event_id = attr.ib(type=str)
-    room_id = attr.ib(type=str)
-    type = attr.ib(type=str)
-    state_key = attr.ib(type=Optional[str])
-    redacts = attr.ib(type=Optional[str])
-    relates_to = attr.ib(type=Optional[str])
-    membership = attr.ib(type=Optional[str])
-    rejected = attr.ib(type=bool)
+    event_id: str
+    room_id: str
+    type: str
+    state_key: Optional[str]
+    redacts: Optional[str]
+    relates_to: Optional[str]
+    membership: Optional[str]
+    rejected: bool
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class EventsStreamCurrentStateRow(BaseEventsStreamRow):
     TypeId = "state"
 
-    room_id = attr.ib()  # str
-    type = attr.ib()  # str
-    state_key = attr.ib()  # str
-    event_id = attr.ib()  # str, optional
+    room_id: str
+    type: str
+    state_key: str
+    event_id: Optional[str]
 
 
 _EventRows: Tuple[Type[BaseEventsStreamRow], ...] = (
diff --git a/synapse/rest/admin/background_updates.py b/synapse/rest/admin/background_updates.py
index 6ec00ce0b9..e9bce22a34 100644
--- a/synapse/rest/admin/background_updates.py
+++ b/synapse/rest/admin/background_updates.py
@@ -123,34 +123,25 @@ class BackgroundUpdateStartJobRestServlet(RestServlet):
         job_name = body["job_name"]
 
         if job_name == "populate_stats_process_rooms":
-            jobs = [
-                {
-                    "update_name": "populate_stats_process_rooms",
-                    "progress_json": "{}",
-                },
-            ]
+            jobs = [("populate_stats_process_rooms", "{}", "")]
         elif job_name == "regenerate_directory":
             jobs = [
-                {
-                    "update_name": "populate_user_directory_createtables",
-                    "progress_json": "{}",
-                    "depends_on": "",
-                },
-                {
-                    "update_name": "populate_user_directory_process_rooms",
-                    "progress_json": "{}",
-                    "depends_on": "populate_user_directory_createtables",
-                },
-                {
-                    "update_name": "populate_user_directory_process_users",
-                    "progress_json": "{}",
-                    "depends_on": "populate_user_directory_process_rooms",
-                },
-                {
-                    "update_name": "populate_user_directory_cleanup",
-                    "progress_json": "{}",
-                    "depends_on": "populate_user_directory_process_users",
-                },
+                ("populate_user_directory_createtables", "{}", ""),
+                (
+                    "populate_user_directory_process_rooms",
+                    "{}",
+                    "populate_user_directory_createtables",
+                ),
+                (
+                    "populate_user_directory_process_users",
+                    "{}",
+                    "populate_user_directory_process_rooms",
+                ),
+                (
+                    "populate_user_directory_cleanup",
+                    "{}",
+                    "populate_user_directory_process_users",
+                ),
             ]
         else:
             raise SynapseError(HTTPStatus.BAD_REQUEST, "Invalid job_name")
@@ -158,6 +149,7 @@ class BackgroundUpdateStartJobRestServlet(RestServlet):
         try:
             await self._store.db_pool.simple_insert_many(
                 table="background_updates",
+                keys=("update_name", "progress_json", "depends_on"),
                 values=jobs,
                 desc=f"admin_api_run_{job_name}",
             )
diff --git a/synapse/rest/admin/federation.py b/synapse/rest/admin/federation.py
index 50d88c9109..8cd3fa189e 100644
--- a/synapse/rest/admin/federation.py
+++ b/synapse/rest/admin/federation.py
@@ -111,25 +111,37 @@ class DestinationsRestServlet(RestServlet):
     ) -> Tuple[int, JsonDict]:
         await assert_requester_is_admin(self._auth, request)
 
+        if not await self._store.is_destination_known(destination):
+            raise NotFoundError("Unknown destination")
+
         destination_retry_timings = await self._store.get_destination_retry_timings(
             destination
         )
 
-        if not destination_retry_timings:
-            raise NotFoundError("Unknown destination")
-
         last_successful_stream_ordering = (
             await self._store.get_destination_last_successful_stream_ordering(
                 destination
             )
         )
 
-        response = {
+        response: JsonDict = {
             "destination": destination,
-            "failure_ts": destination_retry_timings.failure_ts,
-            "retry_last_ts": destination_retry_timings.retry_last_ts,
-            "retry_interval": destination_retry_timings.retry_interval,
             "last_successful_stream_ordering": last_successful_stream_ordering,
         }
 
+        if destination_retry_timings:
+            response = {
+                **response,
+                "failure_ts": destination_retry_timings.failure_ts,
+                "retry_last_ts": destination_retry_timings.retry_last_ts,
+                "retry_interval": destination_retry_timings.retry_interval,
+            }
+        else:
+            response = {
+                **response,
+                "failure_ts": None,
+                "retry_last_ts": 0,
+                "retry_interval": 0,
+            }
+
         return HTTPStatus.OK, response
diff --git a/synapse/rest/admin/media.py b/synapse/rest/admin/media.py
index 7236e4027f..299f5c9eb0 100644
--- a/synapse/rest/admin/media.py
+++ b/synapse/rest/admin/media.py
@@ -466,7 +466,7 @@ class UserMediaRestServlet(RestServlet):
         )
 
         deleted_media, total = await self.media_repository.delete_local_media_ids(
-            ([row["media_id"] for row in media])
+            [row["media_id"] for row in media]
         )
 
         return HTTPStatus.OK, {"deleted_media": deleted_media, "total": total}
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 6030373ebc..2e714ac87b 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -424,7 +424,7 @@ class RoomStateRestServlet(RestServlet):
         event_ids = await self.store.get_current_state_ids(room_id)
         events = await self.store.get_events(event_ids.values())
         now = self.clock.time_msec()
-        room_state = await self._event_serializer.serialize_events(events.values(), now)
+        room_state = self._event_serializer.serialize_events(events.values(), now)
         ret = {"state": room_state}
 
         return HTTPStatus.OK, ret
@@ -744,22 +744,22 @@ class RoomEventContextServlet(RestServlet):
             )
 
         time_now = self.clock.time_msec()
-        results["events_before"] = await self._event_serializer.serialize_events(
+        results["events_before"] = self._event_serializer.serialize_events(
             results["events_before"],
             time_now,
-            bundle_aggregations=True,
+            bundle_aggregations=results["aggregations"],
         )
-        results["event"] = await self._event_serializer.serialize_event(
+        results["event"] = self._event_serializer.serialize_event(
             results["event"],
             time_now,
-            bundle_aggregations=True,
+            bundle_aggregations=results["aggregations"],
         )
-        results["events_after"] = await self._event_serializer.serialize_events(
+        results["events_after"] = self._event_serializer.serialize_events(
             results["events_after"],
             time_now,
-            bundle_aggregations=True,
+            bundle_aggregations=results["aggregations"],
         )
-        results["state"] = await self._event_serializer.serialize_events(
+        results["state"] = self._event_serializer.serialize_events(
             results["state"], time_now
         )
 
diff --git a/synapse/rest/admin/users.py b/synapse/rest/admin/users.py
index 78e795c347..c2617ee30c 100644
--- a/synapse/rest/admin/users.py
+++ b/synapse/rest/admin/users.py
@@ -173,12 +173,11 @@ class UserRestServletV2(RestServlet):
         if not self.hs.is_mine(target_user):
             raise SynapseError(HTTPStatus.BAD_REQUEST, "Can only look up local users")
 
-        ret = await self.admin_handler.get_user(target_user)
-
-        if not ret:
+        user_info_dict = await self.admin_handler.get_user(target_user)
+        if not user_info_dict:
             raise NotFoundError("User not found")
 
-        return HTTPStatus.OK, ret
+        return HTTPStatus.OK, user_info_dict
 
     async def on_PUT(
         self, request: SynapseRequest, user_id: str
@@ -399,10 +398,10 @@ class UserRestServletV2(RestServlet):
                     target_user, requester, body["avatar_url"], True
                 )
 
-            user = await self.admin_handler.get_user(target_user)
-            assert user is not None
+            user_info_dict = await self.admin_handler.get_user(target_user)
+            assert user_info_dict is not None
 
-            return 201, user
+            return HTTPStatus.CREATED, user_info_dict
 
 
 class UserRegisterServlet(RestServlet):
diff --git a/synapse/rest/client/events.py b/synapse/rest/client/events.py
index 13b72a045a..672c821061 100644
--- a/synapse/rest/client/events.py
+++ b/synapse/rest/client/events.py
@@ -91,7 +91,7 @@ class EventRestServlet(RestServlet):
 
         time_now = self.clock.time_msec()
         if event:
-            result = await self._event_serializer.serialize_event(event, time_now)
+            result = self._event_serializer.serialize_event(event, time_now)
             return 200, result
         else:
             return 404, "Event not found."
diff --git a/synapse/rest/client/notifications.py b/synapse/rest/client/notifications.py
index acd0c9e135..8e427a96a3 100644
--- a/synapse/rest/client/notifications.py
+++ b/synapse/rest/client/notifications.py
@@ -72,7 +72,7 @@ class NotificationsServlet(RestServlet):
                 "actions": pa.actions,
                 "ts": pa.received_ts,
                 "event": (
-                    await self._event_serializer.serialize_event(
+                    self._event_serializer.serialize_event(
                         notif_events[pa.event_id],
                         self.clock.time_msec(),
                         event_format=format_event_for_client_v2_without_room_id,
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index 5815650ee6..8cf5ebaa07 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -19,28 +19,20 @@ any time to reflect changes in the MSC.
 """
 
 import logging
-from typing import TYPE_CHECKING, Awaitable, Optional, Tuple
+from typing import TYPE_CHECKING, Optional, Tuple
 
-from synapse.api.constants import EventTypes, RelationTypes
-from synapse.api.errors import ShadowBanError, SynapseError
+from synapse.api.constants import RelationTypes
+from synapse.api.errors import SynapseError
 from synapse.http.server import HttpServer
-from synapse.http.servlet import (
-    RestServlet,
-    parse_integer,
-    parse_json_object_from_request,
-    parse_string,
-)
+from synapse.http.servlet import RestServlet, parse_integer, parse_string
 from synapse.http.site import SynapseRequest
-from synapse.rest.client.transactions import HttpTransactionCache
+from synapse.rest.client._base import client_patterns
 from synapse.storage.relations import (
     AggregationPaginationToken,
     PaginationChunk,
     RelationPaginationToken,
 )
 from synapse.types import JsonDict
-from synapse.util.stringutils import random_string
-
-from ._base import client_patterns
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -48,112 +40,6 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
-class RelationSendServlet(RestServlet):
-    """Helper API for sending events that have relation data.
-
-    Example API shape to send a 👍 reaction to a room:
-
-        POST /rooms/!foo/send_relation/$bar/m.annotation/m.reaction?key=%F0%9F%91%8D
-        {}
-
-        {
-            "event_id": "$foobar"
-        }
-    """
-
-    PATTERN = (
-        "/rooms/(?P<room_id>[^/]*)/send_relation"
-        "/(?P<parent_id>[^/]*)/(?P<relation_type>[^/]*)/(?P<event_type>[^/]*)"
-    )
-
-    def __init__(self, hs: "HomeServer"):
-        super().__init__()
-        self.auth = hs.get_auth()
-        self.event_creation_handler = hs.get_event_creation_handler()
-        self.txns = HttpTransactionCache(hs)
-
-    def register(self, http_server: HttpServer) -> None:
-        http_server.register_paths(
-            "POST",
-            client_patterns(self.PATTERN + "$", releases=()),
-            self.on_PUT_or_POST,
-            self.__class__.__name__,
-        )
-        http_server.register_paths(
-            "PUT",
-            client_patterns(self.PATTERN + "/(?P<txn_id>[^/]*)$", releases=()),
-            self.on_PUT,
-            self.__class__.__name__,
-        )
-
-    def on_PUT(
-        self,
-        request: SynapseRequest,
-        room_id: str,
-        parent_id: str,
-        relation_type: str,
-        event_type: str,
-        txn_id: Optional[str] = None,
-    ) -> Awaitable[Tuple[int, JsonDict]]:
-        return self.txns.fetch_or_execute_request(
-            request,
-            self.on_PUT_or_POST,
-            request,
-            room_id,
-            parent_id,
-            relation_type,
-            event_type,
-            txn_id,
-        )
-
-    async def on_PUT_or_POST(
-        self,
-        request: SynapseRequest,
-        room_id: str,
-        parent_id: str,
-        relation_type: str,
-        event_type: str,
-        txn_id: Optional[str] = None,
-    ) -> Tuple[int, JsonDict]:
-        requester = await self.auth.get_user_by_req(request, allow_guest=True)
-
-        if event_type == EventTypes.Member:
-            # Add relations to a membership is meaningless, so we just deny it
-            # at the CS API rather than trying to handle it correctly.
-            raise SynapseError(400, "Cannot send member events with relations")
-
-        content = parse_json_object_from_request(request)
-
-        aggregation_key = parse_string(request, "key", encoding="utf-8")
-
-        content["m.relates_to"] = {
-            "event_id": parent_id,
-            "rel_type": relation_type,
-        }
-        if aggregation_key is not None:
-            content["m.relates_to"]["key"] = aggregation_key
-
-        event_dict = {
-            "type": event_type,
-            "content": content,
-            "room_id": room_id,
-            "sender": requester.user.to_string(),
-        }
-
-        try:
-            (
-                event,
-                _,
-            ) = await self.event_creation_handler.create_and_send_nonmember_event(
-                requester, event_dict=event_dict, txn_id=txn_id
-            )
-            event_id = event.event_id
-        except ShadowBanError:
-            event_id = "$" + random_string(43)
-
-        return 200, {"event_id": event_id}
-
-
 class RelationPaginationServlet(RestServlet):
     """API to paginate relations on an event by topological ordering, optionally
     filtered by relation type and event type.
@@ -227,13 +113,16 @@ class RelationPaginationServlet(RestServlet):
         now = self.clock.time_msec()
         # Do not bundle aggregations when retrieving the original event because
         # we want the content before relations are applied to it.
-        original_event = await self._event_serializer.serialize_event(
-            event, now, bundle_aggregations=False
+        original_event = self._event_serializer.serialize_event(
+            event, now, bundle_aggregations=None
         )
         # The relations returned for the requested event do include their
         # bundled aggregations.
-        serialized_events = await self._event_serializer.serialize_events(
-            events, now, bundle_aggregations=True
+        aggregations = await self.store.get_bundled_aggregations(
+            events, requester.user.to_string()
+        )
+        serialized_events = self._event_serializer.serialize_events(
+            events, now, bundle_aggregations=aggregations
         )
 
         return_value = pagination_chunk.to_dict()
@@ -422,7 +311,7 @@ class RelationAggregationGroupPaginationServlet(RestServlet):
         )
 
         now = self.clock.time_msec()
-        serialized_events = await self._event_serializer.serialize_events(events, now)
+        serialized_events = self._event_serializer.serialize_events(events, now)
 
         return_value = result.to_dict()
         return_value["chunk"] = serialized_events
@@ -431,7 +320,6 @@ class RelationAggregationGroupPaginationServlet(RestServlet):
 
 
 def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
-    RelationSendServlet(hs).register(http_server)
     RelationPaginationServlet(hs).register(http_server)
     RelationAggregationPaginationServlet(hs).register(http_server)
     RelationAggregationGroupPaginationServlet(hs).register(http_server)
diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index 40330749e5..31fd329a38 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -642,6 +642,7 @@ class RoomEventServlet(RestServlet):
     def __init__(self, hs: "HomeServer"):
         super().__init__()
         self.clock = hs.get_clock()
+        self._store = hs.get_datastore()
         self.event_handler = hs.get_event_handler()
         self._event_serializer = hs.get_event_client_serializer()
         self.auth = hs.get_auth()
@@ -660,10 +661,15 @@ class RoomEventServlet(RestServlet):
             # https://matrix.org/docs/spec/client_server/r0.5.0#get-matrix-client-r0-rooms-roomid-event-eventid
             raise SynapseError(404, "Event not found.", errcode=Codes.NOT_FOUND)
 
-        time_now = self.clock.time_msec()
         if event:
-            event_dict = await self._event_serializer.serialize_event(
-                event, time_now, bundle_aggregations=True
+            # Ensure there are bundled aggregations available.
+            aggregations = await self._store.get_bundled_aggregations(
+                [event], requester.user.to_string()
+            )
+
+            time_now = self.clock.time_msec()
+            event_dict = self._event_serializer.serialize_event(
+                event, time_now, bundle_aggregations=aggregations
             )
             return 200, event_dict
 
@@ -708,16 +714,20 @@ class RoomEventContextServlet(RestServlet):
             raise SynapseError(404, "Event not found.", errcode=Codes.NOT_FOUND)
 
         time_now = self.clock.time_msec()
-        results["events_before"] = await self._event_serializer.serialize_events(
-            results["events_before"], time_now, bundle_aggregations=True
+        results["events_before"] = self._event_serializer.serialize_events(
+            results["events_before"],
+            time_now,
+            bundle_aggregations=results["aggregations"],
         )
-        results["event"] = await self._event_serializer.serialize_event(
-            results["event"], time_now, bundle_aggregations=True
+        results["event"] = self._event_serializer.serialize_event(
+            results["event"], time_now, bundle_aggregations=results["aggregations"]
         )
-        results["events_after"] = await self._event_serializer.serialize_events(
-            results["events_after"], time_now, bundle_aggregations=True
+        results["events_after"] = self._event_serializer.serialize_events(
+            results["events_after"],
+            time_now,
+            bundle_aggregations=results["aggregations"],
         )
-        results["state"] = await self._event_serializer.serialize_events(
+        results["state"] = self._event_serializer.serialize_events(
             results["state"], time_now
         )
 
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index e99a943d0d..d20ae1421e 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -17,7 +17,6 @@ from collections import defaultdict
 from typing import (
     TYPE_CHECKING,
     Any,
-    Awaitable,
     Callable,
     Dict,
     Iterable,
@@ -395,7 +394,7 @@ class SyncRestServlet(RestServlet):
         """
         invited = {}
         for room in rooms:
-            invite = await self._event_serializer.serialize_event(
+            invite = self._event_serializer.serialize_event(
                 room.invite,
                 time_now,
                 token_id=token_id,
@@ -432,7 +431,7 @@ class SyncRestServlet(RestServlet):
         """
         knocked = {}
         for room in rooms:
-            knock = await self._event_serializer.serialize_event(
+            knock = self._event_serializer.serialize_event(
                 room.knock,
                 time_now,
                 token_id=token_id,
@@ -525,21 +524,14 @@ class SyncRestServlet(RestServlet):
             The room, encoded in our response format
         """
 
-        def serialize(events: Iterable[EventBase]) -> Awaitable[List[JsonDict]]:
+        def serialize(
+            events: Iterable[EventBase],
+            aggregations: Optional[Dict[str, Dict[str, Any]]] = None,
+        ) -> List[JsonDict]:
             return self._event_serializer.serialize_events(
                 events,
                 time_now=time_now,
-                # Don't bother to bundle aggregations if the timeline is unlimited,
-                # as clients will have all the necessary information.
-                # bundle_aggregations=room.timeline.limited,
-                #
-                # richvdh 2021-12-15: disable this temporarily as it has too high an
-                # overhead for initialsyncs. We need to figure out a way that the
-                # bundling can be done *before* the events are stored in the
-                # SyncResponseCache so that this part can be synchronous.
-                #
-                # Ensure to re-enable the test at tests/rest/client/test_relations.py::RelationsTestCase.test_bundled_aggregations.
-                bundle_aggregations=False,
+                bundle_aggregations=aggregations,
                 token_id=token_id,
                 event_format=event_formatter,
                 only_event_fields=only_fields,
@@ -561,8 +553,10 @@ class SyncRestServlet(RestServlet):
                     event.room_id,
                 )
 
-        serialized_state = await serialize(state_events)
-        serialized_timeline = await serialize(timeline_events)
+        serialized_state = serialize(state_events)
+        serialized_timeline = serialize(
+            timeline_events, room.timeline.bundled_aggregations
+        )
 
         account_data = room.account_data
 
diff --git a/synapse/rest/media/v1/media_storage.py b/synapse/rest/media/v1/media_storage.py
index fca239d8c7..9f6c251caf 100644
--- a/synapse/rest/media/v1/media_storage.py
+++ b/synapse/rest/media/v1/media_storage.py
@@ -343,7 +343,7 @@ class SpamMediaException(NotFoundError):
     """
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class ReadableFileWrapper:
     """Wrapper that allows reading a file in chunks, yielding to the reactor,
     and writing to a callback.
@@ -354,8 +354,8 @@ class ReadableFileWrapper:
 
     CHUNK_SIZE = 2 ** 14
 
-    clock = attr.ib(type=Clock)
-    path = attr.ib(type=str)
+    clock: Clock
+    path: str
 
     async def write_chunks_to(self, callback: Callable[[bytes], None]) -> None:
         """Reads the file in chunks and calls the callback with each chunk."""
diff --git a/synapse/server.py b/synapse/server.py
index 185e40e4da..3032f0b738 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -759,7 +759,7 @@ class HomeServer(metaclass=abc.ABCMeta):
 
     @cache_in_self
     def get_event_client_serializer(self) -> EventClientSerializer:
-        return EventClientSerializer(self)
+        return EventClientSerializer()
 
     @cache_in_self
     def get_password_policy_handler(self) -> PasswordPolicyHandler:
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index 69ac8c3423..67e8bc6ec2 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -45,7 +45,6 @@ from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, StateResolutionVersio
 from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.logging.context import ContextResourceUsage
-from synapse.logging.utils import log_function
 from synapse.state import v1, v2
 from synapse.storage.databases.main.events_worker import EventRedactBehaviour
 from synapse.storage.roommember import ProfileInfo
@@ -450,19 +449,19 @@ class StateHandler:
         return {key: state_map[ev_id] for key, ev_id in new_state.items()}
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _StateResMetrics:
     """Keeps track of some usage metrics about state res."""
 
     # System and User CPU time, in seconds
-    cpu_time = attr.ib(type=float, default=0.0)
+    cpu_time: float = 0.0
 
     # time spent on database transactions (excluding scheduling time). This roughly
     # corresponds to the amount of work done on the db server, excluding event fetches.
-    db_time = attr.ib(type=float, default=0.0)
+    db_time: float = 0.0
 
     # number of events fetched from the db.
-    db_events = attr.ib(type=int, default=0)
+    db_events: int = 0
 
 
 _biggest_room_by_cpu_counter = Counter(
@@ -512,7 +511,6 @@ class StateResolutionHandler:
 
         self.clock.looping_call(self._report_metrics, 120 * 1000)
 
-    @log_function
     async def resolve_state_groups(
         self,
         room_id: str,
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 2cacc7dd6c..57cc1d76e0 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -143,7 +143,7 @@ def make_conn(
     return db_conn
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class LoggingDatabaseConnection:
     """A wrapper around a database connection that returns `LoggingTransaction`
     as its cursor class.
@@ -151,9 +151,9 @@ class LoggingDatabaseConnection:
     This is mainly used on startup to ensure that queries get logged correctly
     """
 
-    conn = attr.ib(type=Connection)
-    engine = attr.ib(type=BaseDatabaseEngine)
-    default_txn_name = attr.ib(type=str)
+    conn: Connection
+    engine: BaseDatabaseEngine
+    default_txn_name: str
 
     def cursor(
         self, *, txn_name=None, after_callbacks=None, exception_callbacks=None
@@ -934,56 +934,6 @@ class DatabasePool:
         txn.execute(sql, vals)
 
     async def simple_insert_many(
-        self, table: str, values: List[Dict[str, Any]], desc: str
-    ) -> None:
-        """Executes an INSERT query on the named table.
-
-        The input is given as a list of dicts, with one dict per row.
-        Generally simple_insert_many_values should be preferred for new code.
-
-        Args:
-            table: string giving the table name
-            values: dict of new column names and values for them
-            desc: description of the transaction, for logging and metrics
-        """
-        await self.runInteraction(desc, self.simple_insert_many_txn, table, values)
-
-    @staticmethod
-    def simple_insert_many_txn(
-        txn: LoggingTransaction, table: str, values: List[Dict[str, Any]]
-    ) -> None:
-        """Executes an INSERT query on the named table.
-
-        The input is given as a list of dicts, with one dict per row.
-        Generally simple_insert_many_values_txn should be preferred for new code.
-
-        Args:
-            txn: The transaction to use.
-            table: string giving the table name
-            values: dict of new column names and values for them
-        """
-        if not values:
-            return
-
-        # This is a *slight* abomination to get a list of tuples of key names
-        # and a list of tuples of value names.
-        #
-        # i.e. [{"a": 1, "b": 2}, {"c": 3, "d": 4}]
-        #         => [("a", "b",), ("c", "d",)] and [(1, 2,), (3, 4,)]
-        #
-        # The sort is to ensure that we don't rely on dictionary iteration
-        # order.
-        keys, vals = zip(
-            *(zip(*(sorted(i.items(), key=lambda kv: kv[0]))) for i in values if i)
-        )
-
-        for k in keys:
-            if k != keys[0]:
-                raise RuntimeError("All items must have the same keys")
-
-        return DatabasePool.simple_insert_many_values_txn(txn, table, keys[0], vals)
-
-    async def simple_insert_many_values(
         self,
         table: str,
         keys: Collection[str],
@@ -1002,11 +952,11 @@ class DatabasePool:
             desc: description of the transaction, for logging and metrics
         """
         await self.runInteraction(
-            desc, self.simple_insert_many_values_txn, table, keys, values
+            desc, self.simple_insert_many_txn, table, keys, values
         )
 
     @staticmethod
-    def simple_insert_many_values_txn(
+    def simple_insert_many_txn(
         txn: LoggingTransaction,
         table: str,
         keys: Collection[str],
diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index 32a553fdd7..ef475e18c7 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -450,7 +450,7 @@ class AccountDataWorkerStore(CacheInvalidationWorkerStore):
     async def add_account_data_for_user(
         self, user_id: str, account_data_type: str, content: JsonDict
     ) -> int:
-        """Add some account_data to a room for a user.
+        """Add some global account_data for a user.
 
         Args:
             user_id: The user to add a tag for.
@@ -536,9 +536,9 @@ class AccountDataWorkerStore(CacheInvalidationWorkerStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="ignored_users",
+            keys=("ignorer_user_id", "ignored_user_id"),
             values=[
-                {"ignorer_user_id": user_id, "ignored_user_id": u}
-                for u in currently_ignored_users - previously_ignored_users
+                (user_id, u) for u in currently_ignored_users - previously_ignored_users
             ],
         )
 
diff --git a/synapse/storage/databases/main/deviceinbox.py b/synapse/storage/databases/main/deviceinbox.py
index 3682cb6a81..4eca97189b 100644
--- a/synapse/storage/databases/main/deviceinbox.py
+++ b/synapse/storage/databases/main/deviceinbox.py
@@ -432,14 +432,21 @@ class DeviceInboxWorkerStore(SQLBaseStore):
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="device_federation_outbox",
+                keys=(
+                    "destination",
+                    "stream_id",
+                    "queued_ts",
+                    "messages_json",
+                    "instance_name",
+                ),
                 values=[
-                    {
-                        "destination": destination,
-                        "stream_id": stream_id,
-                        "queued_ts": now_ms,
-                        "messages_json": json_encoder.encode(edu),
-                        "instance_name": self._instance_name,
-                    }
+                    (
+                        destination,
+                        stream_id,
+                        now_ms,
+                        json_encoder.encode(edu),
+                        self._instance_name,
+                    )
                     for destination, edu in remote_messages_by_destination.items()
                 ],
             )
@@ -571,14 +578,9 @@ class DeviceInboxWorkerStore(SQLBaseStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="device_inbox",
+            keys=("user_id", "device_id", "stream_id", "message_json", "instance_name"),
             values=[
-                {
-                    "user_id": user_id,
-                    "device_id": device_id,
-                    "stream_id": stream_id,
-                    "message_json": message_json,
-                    "instance_name": self._instance_name,
-                }
+                (user_id, device_id, stream_id, message_json, self._instance_name)
                 for user_id, messages_by_device in local_by_user_then_device.items()
                 for device_id, message_json in messages_by_device.items()
             ],
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index bc7e876047..8f0cd0695f 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -781,7 +781,7 @@ class DeviceWorkerStore(SQLBaseStore):
     @cached(max_entries=10000)
     async def get_device_list_last_stream_id_for_remote(
         self, user_id: str
-    ) -> Optional[Any]:
+    ) -> Optional[str]:
         """Get the last stream_id we got for a user. May be None if we haven't
         got any information for them.
         """
@@ -797,7 +797,9 @@ class DeviceWorkerStore(SQLBaseStore):
         cached_method_name="get_device_list_last_stream_id_for_remote",
         list_name="user_ids",
     )
-    async def get_device_list_last_stream_id_for_remotes(self, user_ids: Iterable[str]):
+    async def get_device_list_last_stream_id_for_remotes(
+        self, user_ids: Iterable[str]
+    ) -> Dict[str, Optional[str]]:
         rows = await self.db_pool.simple_select_many_batch(
             table="device_lists_remote_extremeties",
             column="user_id",
@@ -1384,6 +1386,7 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
         content: JsonDict,
         stream_id: str,
     ) -> None:
+        """Delete, update or insert a cache entry for this (user, device) pair."""
         if content.get("deleted"):
             self.db_pool.simple_delete_txn(
                 txn,
@@ -1443,6 +1446,7 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
     def _update_remote_device_list_cache_txn(
         self, txn: LoggingTransaction, user_id: str, devices: List[dict], stream_id: int
     ) -> None:
+        """Replace the list of cached devices for this user with the given list."""
         self.db_pool.simple_delete_txn(
             txn, table="device_lists_remote_cache", keyvalues={"user_id": user_id}
         )
@@ -1450,12 +1454,9 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="device_lists_remote_cache",
+            keys=("user_id", "device_id", "content"),
             values=[
-                {
-                    "user_id": user_id,
-                    "device_id": content["device_id"],
-                    "content": json_encoder.encode(content),
-                }
+                (user_id, content["device_id"], json_encoder.encode(content))
                 for content in devices
             ],
         )
@@ -1543,8 +1544,9 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="device_lists_stream",
+            keys=("stream_id", "user_id", "device_id"),
             values=[
-                {"stream_id": stream_id, "user_id": user_id, "device_id": device_id}
+                (stream_id, user_id, device_id)
                 for stream_id, device_id in zip(stream_ids, device_ids)
             ],
         )
@@ -1571,18 +1573,27 @@ class DeviceStore(DeviceWorkerStore, DeviceBackgroundUpdateStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="device_lists_outbound_pokes",
+            keys=(
+                "destination",
+                "stream_id",
+                "user_id",
+                "device_id",
+                "sent",
+                "ts",
+                "opentracing_context",
+            ),
             values=[
-                {
-                    "destination": destination,
-                    "stream_id": next(next_stream_id),
-                    "user_id": user_id,
-                    "device_id": device_id,
-                    "sent": False,
-                    "ts": now,
-                    "opentracing_context": json_encoder.encode(context)
+                (
+                    destination,
+                    next(next_stream_id),
+                    user_id,
+                    device_id,
+                    False,
+                    now,
+                    json_encoder.encode(context)
                     if whitelisted_homeserver(destination)
                     else "{}",
-                }
+                )
                 for destination in hosts
                 for device_id in device_ids
             ],
diff --git a/synapse/storage/databases/main/directory.py b/synapse/storage/databases/main/directory.py
index f76c6121e8..5903fdaf00 100644
--- a/synapse/storage/databases/main/directory.py
+++ b/synapse/storage/databases/main/directory.py
@@ -112,10 +112,8 @@ class DirectoryWorkerStore(CacheInvalidationWorkerStore):
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="room_alias_servers",
-                values=[
-                    {"room_alias": room_alias.to_string(), "server": server}
-                    for server in servers
-                ],
+                keys=("room_alias", "server"),
+                values=[(room_alias.to_string(), server) for server in servers],
             )
 
             self._invalidate_cache_and_stream(
diff --git a/synapse/storage/databases/main/e2e_room_keys.py b/synapse/storage/databases/main/e2e_room_keys.py
index 0cb48b9dd7..b789a588a5 100644
--- a/synapse/storage/databases/main/e2e_room_keys.py
+++ b/synapse/storage/databases/main/e2e_room_keys.py
@@ -110,16 +110,16 @@ class EndToEndRoomKeyStore(SQLBaseStore):
         values = []
         for (room_id, session_id, room_key) in room_keys:
             values.append(
-                {
-                    "user_id": user_id,
-                    "version": version_int,
-                    "room_id": room_id,
-                    "session_id": session_id,
-                    "first_message_index": room_key["first_message_index"],
-                    "forwarded_count": room_key["forwarded_count"],
-                    "is_verified": room_key["is_verified"],
-                    "session_data": json_encoder.encode(room_key["session_data"]),
-                }
+                (
+                    user_id,
+                    version_int,
+                    room_id,
+                    session_id,
+                    room_key["first_message_index"],
+                    room_key["forwarded_count"],
+                    room_key["is_verified"],
+                    json_encoder.encode(room_key["session_data"]),
+                )
             )
             log_kv(
                 {
@@ -131,7 +131,19 @@ class EndToEndRoomKeyStore(SQLBaseStore):
             )
 
         await self.db_pool.simple_insert_many(
-            table="e2e_room_keys", values=values, desc="add_e2e_room_keys"
+            table="e2e_room_keys",
+            keys=(
+                "user_id",
+                "version",
+                "room_id",
+                "session_id",
+                "first_message_index",
+                "forwarded_count",
+                "is_verified",
+                "session_data",
+            ),
+            values=values,
+            desc="add_e2e_room_keys",
         )
 
     @trace
diff --git a/synapse/storage/databases/main/end_to_end_keys.py b/synapse/storage/databases/main/end_to_end_keys.py
index 57b5ffbad3..1f8447b507 100644
--- a/synapse/storage/databases/main/end_to_end_keys.py
+++ b/synapse/storage/databases/main/end_to_end_keys.py
@@ -50,16 +50,16 @@ if TYPE_CHECKING:
     from synapse.server import HomeServer
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class DeviceKeyLookupResult:
     """The type returned by get_e2e_device_keys_and_signatures"""
 
-    display_name = attr.ib(type=Optional[str])
+    display_name: Optional[str]
 
     # the key data from e2e_device_keys_json. Typically includes fields like
     # "algorithm", "keys" (including the curve25519 identity key and the ed25519 signing
     # key) and "signatures" (a map from (user id) to (key id/device_id) to signature.)
-    keys = attr.ib(type=Optional[JsonDict])
+    keys: Optional[JsonDict]
 
 
 class EndToEndKeyBackgroundStore(SQLBaseStore):
@@ -387,15 +387,16 @@ class EndToEndKeyWorkerStore(EndToEndKeyBackgroundStore, CacheInvalidationWorker
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="e2e_one_time_keys_json",
+                keys=(
+                    "user_id",
+                    "device_id",
+                    "algorithm",
+                    "key_id",
+                    "ts_added_ms",
+                    "key_json",
+                ),
                 values=[
-                    {
-                        "user_id": user_id,
-                        "device_id": device_id,
-                        "algorithm": algorithm,
-                        "key_id": key_id,
-                        "ts_added_ms": time_now,
-                        "key_json": json_bytes,
-                    }
+                    (user_id, device_id, algorithm, key_id, time_now, json_bytes)
                     for algorithm, key_id, json_bytes in new_keys
                 ],
             )
@@ -1186,15 +1187,22 @@ class EndToEndKeyStore(EndToEndKeyWorkerStore, SQLBaseStore):
         """
         await self.db_pool.simple_insert_many(
             "e2e_cross_signing_signatures",
-            [
-                {
-                    "user_id": user_id,
-                    "key_id": item.signing_key_id,
-                    "target_user_id": item.target_user_id,
-                    "target_device_id": item.target_device_id,
-                    "signature": item.signature,
-                }
+            keys=(
+                "user_id",
+                "key_id",
+                "target_user_id",
+                "target_device_id",
+                "signature",
+            ),
+            values=[
+                (
+                    user_id,
+                    item.signing_key_id,
+                    item.target_user_id,
+                    item.target_device_id,
+                    item.signature,
+                )
                 for item in signatures
             ],
-            "add_e2e_signing_key",
+            desc="add_e2e_signing_key",
         )
diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index a98e6b2593..b7c4c62222 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -875,14 +875,21 @@ class EventPushActionsWorkerStore(SQLBaseStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="event_push_summary",
+            keys=(
+                "user_id",
+                "room_id",
+                "notif_count",
+                "unread_count",
+                "stream_ordering",
+            ),
             values=[
-                {
-                    "user_id": user_id,
-                    "room_id": room_id,
-                    "notif_count": summary.notif_count,
-                    "unread_count": summary.unread_count,
-                    "stream_ordering": summary.stream_ordering,
-                }
+                (
+                    user_id,
+                    room_id,
+                    summary.notif_count,
+                    summary.unread_count,
+                    summary.stream_ordering,
+                )
                 for ((user_id, room_id), summary) in summaries.items()
                 if summary.old_user_id is None
             ],
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index dd255aefb9..7278002322 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -39,7 +39,6 @@ from synapse.api.room_versions import RoomVersions
 from synapse.crypto.event_signing import compute_event_reference_hash
 from synapse.events import EventBase  # noqa: F401
 from synapse.events.snapshot import EventContext  # noqa: F401
-from synapse.logging.utils import log_function
 from synapse.storage._base import db_to_json, make_in_list_sql_clause
 from synapse.storage.database import (
     DatabasePool,
@@ -69,7 +68,7 @@ event_counter = Counter(
 )
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class DeltaState:
     """Deltas to use to update the `current_state_events` table.
 
@@ -80,9 +79,9 @@ class DeltaState:
             should e.g. be removed from `current_state_events` table.
     """
 
-    to_delete = attr.ib(type=List[Tuple[str, str]])
-    to_insert = attr.ib(type=StateMap[str])
-    no_longer_in_room = attr.ib(type=bool, default=False)
+    to_delete: List[Tuple[str, str]]
+    to_insert: StateMap[str]
+    no_longer_in_room: bool = False
 
 
 class PersistEventsStore:
@@ -328,7 +327,6 @@ class PersistEventsStore:
 
         return existing_prevs
 
-    @log_function
     def _persist_events_txn(
         self,
         txn: LoggingTransaction,
@@ -442,12 +440,9 @@ class PersistEventsStore:
         self.db_pool.simple_insert_many_txn(
             txn,
             table="event_auth",
+            keys=("event_id", "room_id", "auth_id"),
             values=[
-                {
-                    "event_id": event.event_id,
-                    "room_id": event.room_id,
-                    "auth_id": auth_id,
-                }
+                (event.event_id, event.room_id, auth_id)
                 for event in events
                 for auth_id in event.auth_event_ids()
                 if event.is_state()
@@ -675,8 +670,9 @@ class PersistEventsStore:
         db_pool.simple_insert_many_txn(
             txn,
             table="event_auth_chains",
+            keys=("event_id", "chain_id", "sequence_number"),
             values=[
-                {"event_id": event_id, "chain_id": c_id, "sequence_number": seq}
+                (event_id, c_id, seq)
                 for event_id, (c_id, seq) in new_chain_tuples.items()
             ],
         )
@@ -782,13 +778,14 @@ class PersistEventsStore:
         db_pool.simple_insert_many_txn(
             txn,
             table="event_auth_chain_links",
+            keys=(
+                "origin_chain_id",
+                "origin_sequence_number",
+                "target_chain_id",
+                "target_sequence_number",
+            ),
             values=[
-                {
-                    "origin_chain_id": source_id,
-                    "origin_sequence_number": source_seq,
-                    "target_chain_id": target_id,
-                    "target_sequence_number": target_seq,
-                }
+                (source_id, source_seq, target_id, target_seq)
                 for (
                     source_id,
                     source_seq,
@@ -943,20 +940,28 @@ class PersistEventsStore:
             txn_id = getattr(event.internal_metadata, "txn_id", None)
             if token_id and txn_id:
                 to_insert.append(
-                    {
-                        "event_id": event.event_id,
-                        "room_id": event.room_id,
-                        "user_id": event.sender,
-                        "token_id": token_id,
-                        "txn_id": txn_id,
-                        "inserted_ts": self._clock.time_msec(),
-                    }
+                    (
+                        event.event_id,
+                        event.room_id,
+                        event.sender,
+                        token_id,
+                        txn_id,
+                        self._clock.time_msec(),
+                    )
                 )
 
         if to_insert:
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="event_txn_id",
+                keys=(
+                    "event_id",
+                    "room_id",
+                    "user_id",
+                    "token_id",
+                    "txn_id",
+                    "inserted_ts",
+                ),
                 values=to_insert,
             )
 
@@ -1161,8 +1166,9 @@ class PersistEventsStore:
         self.db_pool.simple_insert_many_txn(
             txn,
             table="event_forward_extremities",
+            keys=("event_id", "room_id"),
             values=[
-                {"event_id": ev_id, "room_id": room_id}
+                (ev_id, room_id)
                 for room_id, new_extrem in new_forward_extremities.items()
                 for ev_id in new_extrem
             ],
@@ -1174,12 +1180,9 @@ class PersistEventsStore:
         self.db_pool.simple_insert_many_txn(
             txn,
             table="stream_ordering_to_exterm",
+            keys=("room_id", "event_id", "stream_ordering"),
             values=[
-                {
-                    "room_id": room_id,
-                    "event_id": event_id,
-                    "stream_ordering": max_stream_order,
-                }
+                (room_id, event_id, max_stream_order)
                 for room_id, new_extrem in new_forward_extremities.items()
                 for event_id in new_extrem
             ],
@@ -1342,7 +1345,7 @@ class PersistEventsStore:
             d.pop("redacted_because", None)
             return d
 
-        self.db_pool.simple_insert_many_values_txn(
+        self.db_pool.simple_insert_many_txn(
             txn,
             table="event_json",
             keys=("event_id", "room_id", "internal_metadata", "json", "format_version"),
@@ -1358,7 +1361,7 @@ class PersistEventsStore:
             ),
         )
 
-        self.db_pool.simple_insert_many_values_txn(
+        self.db_pool.simple_insert_many_txn(
             txn,
             table="events",
             keys=(
@@ -1412,7 +1415,7 @@ class PersistEventsStore:
         )
         txn.execute(sql + clause, [False] + args)
 
-        self.db_pool.simple_insert_many_values_txn(
+        self.db_pool.simple_insert_many_txn(
             txn,
             table="state_events",
             keys=("event_id", "room_id", "type", "state_key"),
@@ -1622,14 +1625,9 @@ class PersistEventsStore:
         return self.db_pool.simple_insert_many_txn(
             txn=txn,
             table="event_labels",
+            keys=("event_id", "label", "room_id", "topological_ordering"),
             values=[
-                {
-                    "event_id": event_id,
-                    "label": label,
-                    "room_id": room_id,
-                    "topological_ordering": topological_ordering,
-                }
-                for label in labels
+                (event_id, label, room_id, topological_ordering) for label in labels
             ],
         )
 
@@ -1657,16 +1655,13 @@ class PersistEventsStore:
         vals = []
         for event in events:
             ref_alg, ref_hash_bytes = compute_event_reference_hash(event)
-            vals.append(
-                {
-                    "event_id": event.event_id,
-                    "algorithm": ref_alg,
-                    "hash": memoryview(ref_hash_bytes),
-                }
-            )
+            vals.append((event.event_id, ref_alg, memoryview(ref_hash_bytes)))
 
         self.db_pool.simple_insert_many_txn(
-            txn, table="event_reference_hashes", values=vals
+            txn,
+            table="event_reference_hashes",
+            keys=("event_id", "algorithm", "hash"),
+            values=vals,
         )
 
     def _store_room_members_txn(
@@ -1689,18 +1684,25 @@ class PersistEventsStore:
         self.db_pool.simple_insert_many_txn(
             txn,
             table="room_memberships",
+            keys=(
+                "event_id",
+                "user_id",
+                "sender",
+                "room_id",
+                "membership",
+                "display_name",
+                "avatar_url",
+            ),
             values=[
-                {
-                    "event_id": event.event_id,
-                    "user_id": event.state_key,
-                    "sender": event.user_id,
-                    "room_id": event.room_id,
-                    "membership": event.membership,
-                    "display_name": non_null_str_or_none(
-                        event.content.get("displayname")
-                    ),
-                    "avatar_url": non_null_str_or_none(event.content.get("avatar_url")),
-                }
+                (
+                    event.event_id,
+                    event.state_key,
+                    event.user_id,
+                    event.room_id,
+                    event.membership,
+                    non_null_str_or_none(event.content.get("displayname")),
+                    non_null_str_or_none(event.content.get("avatar_url")),
+                )
                 for event in events
             ],
         )
@@ -1791,6 +1793,13 @@ class PersistEventsStore:
             txn.call_after(
                 self.store.get_thread_summary.invalidate, (parent_id, event.room_id)
             )
+            # It should be safe to only invalidate the cache if the user has not
+            # previously participated in the thread, but that's difficult (and
+            # potentially error-prone) so it is always invalidated.
+            txn.call_after(
+                self.store.get_thread_participated.invalidate,
+                (parent_id, event.room_id, event.sender),
+            )
 
     def _handle_insertion_event(self, txn: LoggingTransaction, event: EventBase):
         """Handles keeping track of insertion events and edges/connections.
@@ -2163,13 +2172,9 @@ class PersistEventsStore:
         self.db_pool.simple_insert_many_txn(
             txn,
             table="event_edges",
+            keys=("event_id", "prev_event_id", "room_id", "is_state"),
             values=[
-                {
-                    "event_id": ev.event_id,
-                    "prev_event_id": e_id,
-                    "room_id": ev.room_id,
-                    "is_state": False,
-                }
+                (ev.event_id, e_id, ev.room_id, False)
                 for ev in events
                 for e_id in ev.prev_event_ids()
             ],
@@ -2226,17 +2231,17 @@ class PersistEventsStore:
         )
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _LinkMap:
     """A helper type for tracking links between chains."""
 
     # Stores the set of links as nested maps: source chain ID -> target chain ID
     # -> source sequence number -> target sequence number.
-    maps = attr.ib(type=Dict[int, Dict[int, Dict[int, int]]], factory=dict)
+    maps: Dict[int, Dict[int, Dict[int, int]]] = attr.Factory(dict)
 
     # Stores the links that have been added (with new set to true), as tuples of
     # `(source chain ID, source sequence no, target chain ID, target sequence no.)`
-    additions = attr.ib(type=Set[Tuple[int, int, int, int]], factory=set)
+    additions: Set[Tuple[int, int, int, int]] = attr.Factory(set)
 
     def add_link(
         self,
diff --git a/synapse/storage/databases/main/events_bg_updates.py b/synapse/storage/databases/main/events_bg_updates.py
index a68f14ba48..d5f0059665 100644
--- a/synapse/storage/databases/main/events_bg_updates.py
+++ b/synapse/storage/databases/main/events_bg_updates.py
@@ -65,22 +65,22 @@ class _BackgroundUpdates:
     REPLACE_STREAM_ORDERING_COLUMN = "replace_stream_ordering_column"
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class _CalculateChainCover:
     """Return value for _calculate_chain_cover_txn."""
 
     # The last room_id/depth/stream processed.
-    room_id = attr.ib(type=str)
-    depth = attr.ib(type=int)
-    stream = attr.ib(type=int)
+    room_id: str
+    depth: int
+    stream: int
 
     # Number of rows processed
-    processed_count = attr.ib(type=int)
+    processed_count: int
 
     # Map from room_id to last depth/stream processed for each room that we have
     # processed all events for (i.e. the rooms we can flip the
     # `has_auth_chain_index` for)
-    finished_room_map = attr.ib(type=Dict[str, Tuple[int, int]])
+    finished_room_map: Dict[str, Tuple[int, int]]
 
 
 class EventsBackgroundUpdatesStore(SQLBaseStore):
@@ -684,13 +684,14 @@ class EventsBackgroundUpdatesStore(SQLBaseStore):
                     self.db_pool.simple_insert_many_txn(
                         txn=txn,
                         table="event_labels",
+                        keys=("event_id", "label", "room_id", "topological_ordering"),
                         values=[
-                            {
-                                "event_id": event_id,
-                                "label": label,
-                                "room_id": event_json["room_id"],
-                                "topological_ordering": event_json["depth"],
-                            }
+                            (
+                                event_id,
+                                label,
+                                event_json["room_id"],
+                                event_json["depth"],
+                            )
                             for label in event_json["content"].get(
                                 EventContentFields.LABELS, []
                             )
@@ -803,29 +804,19 @@ class EventsBackgroundUpdatesStore(SQLBaseStore):
 
             if not has_state:
                 state_events.append(
-                    {
-                        "event_id": event.event_id,
-                        "room_id": event.room_id,
-                        "type": event.type,
-                        "state_key": event.state_key,
-                    }
+                    (event.event_id, event.room_id, event.type, event.state_key)
                 )
 
             if not has_event_auth:
                 # Old, dodgy, events may have duplicate auth events, which we
                 # need to deduplicate as we have a unique constraint.
                 for auth_id in set(event.auth_event_ids()):
-                    auth_events.append(
-                        {
-                            "room_id": event.room_id,
-                            "event_id": event.event_id,
-                            "auth_id": auth_id,
-                        }
-                    )
+                    auth_events.append((event.event_id, event.room_id, auth_id))
 
         if state_events:
             await self.db_pool.simple_insert_many(
                 table="state_events",
+                keys=("event_id", "room_id", "type", "state_key"),
                 values=state_events,
                 desc="_rejected_events_metadata_state_events",
             )
@@ -833,6 +824,7 @@ class EventsBackgroundUpdatesStore(SQLBaseStore):
         if auth_events:
             await self.db_pool.simple_insert_many(
                 table="event_auth",
+                keys=("event_id", "room_id", "auth_id"),
                 values=auth_events,
                 desc="_rejected_events_metadata_event_auth",
             )
diff --git a/synapse/storage/databases/main/presence.py b/synapse/storage/databases/main/presence.py
index cbf9ec38f7..4f05811a77 100644
--- a/synapse/storage/databases/main/presence.py
+++ b/synapse/storage/databases/main/presence.py
@@ -129,18 +129,29 @@ class PresenceStore(PresenceBackgroundUpdateStore):
         self.db_pool.simple_insert_many_txn(
             txn,
             table="presence_stream",
+            keys=(
+                "stream_id",
+                "user_id",
+                "state",
+                "last_active_ts",
+                "last_federation_update_ts",
+                "last_user_sync_ts",
+                "status_msg",
+                "currently_active",
+                "instance_name",
+            ),
             values=[
-                {
-                    "stream_id": stream_id,
-                    "user_id": state.user_id,
-                    "state": state.state,
-                    "last_active_ts": state.last_active_ts,
-                    "last_federation_update_ts": state.last_federation_update_ts,
-                    "last_user_sync_ts": state.last_user_sync_ts,
-                    "status_msg": state.status_msg,
-                    "currently_active": state.currently_active,
-                    "instance_name": self._instance_name,
-                }
+                (
+                    stream_id,
+                    state.user_id,
+                    state.state,
+                    state.last_active_ts,
+                    state.last_federation_update_ts,
+                    state.last_user_sync_ts,
+                    state.status_msg,
+                    state.currently_active,
+                    self._instance_name,
+                )
                 for stream_id, state in zip(stream_orderings, presence_states)
             ],
         )
diff --git a/synapse/storage/databases/main/pusher.py b/synapse/storage/databases/main/pusher.py
index 747b4f31df..cf64cd63a4 100644
--- a/synapse/storage/databases/main/pusher.py
+++ b/synapse/storage/databases/main/pusher.py
@@ -561,13 +561,9 @@ class PusherStore(PusherWorkerStore):
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="deleted_pushers",
+                keys=("stream_id", "app_id", "pushkey", "user_id"),
                 values=[
-                    {
-                        "stream_id": stream_id,
-                        "app_id": pusher.app_id,
-                        "pushkey": pusher.pushkey,
-                        "user_id": user_id,
-                    }
+                    (stream_id, pusher.app_id, pusher.pushkey, user_id)
                     for stream_id, pusher in zip(stream_ids, pushers)
                 ],
             )
diff --git a/synapse/storage/databases/main/registration.py b/synapse/storage/databases/main/registration.py
index 4175c82a25..aac94fa464 100644
--- a/synapse/storage/databases/main/registration.py
+++ b/synapse/storage/databases/main/registration.py
@@ -51,7 +51,7 @@ class ExternalIDReuseException(Exception):
     pass
 
 
-@attr.s(frozen=True, slots=True)
+@attr.s(frozen=True, slots=True, auto_attribs=True)
 class TokenLookupResult:
     """Result of looking up an access token.
 
@@ -69,14 +69,14 @@ class TokenLookupResult:
             cached.
     """
 
-    user_id = attr.ib(type=str)
-    is_guest = attr.ib(type=bool, default=False)
-    shadow_banned = attr.ib(type=bool, default=False)
-    token_id = attr.ib(type=Optional[int], default=None)
-    device_id = attr.ib(type=Optional[str], default=None)
-    valid_until_ms = attr.ib(type=Optional[int], default=None)
-    token_owner = attr.ib(type=str)
-    token_used = attr.ib(type=bool, default=False)
+    user_id: str
+    is_guest: bool = False
+    shadow_banned: bool = False
+    token_id: Optional[int] = None
+    device_id: Optional[str] = None
+    valid_until_ms: Optional[int] = None
+    token_owner: str = attr.ib()
+    token_used: bool = False
 
     # Make the token owner default to the user ID, which is the common case.
     @token_owner.default
diff --git a/synapse/storage/databases/main/relations.py b/synapse/storage/databases/main/relations.py
index 4ff6aed253..2cb5d06c13 100644
--- a/synapse/storage/databases/main/relations.py
+++ b/synapse/storage/databases/main/relations.py
@@ -13,14 +13,30 @@
 # limitations under the License.
 
 import logging
-from typing import List, Optional, Tuple, Union, cast
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Dict,
+    Iterable,
+    List,
+    Optional,
+    Tuple,
+    Union,
+    cast,
+)
 
 import attr
+from frozendict import frozendict
 
-from synapse.api.constants import RelationTypes
+from synapse.api.constants import EventTypes, RelationTypes
 from synapse.events import EventBase
 from synapse.storage._base import SQLBaseStore
-from synapse.storage.database import LoggingTransaction, make_in_list_sql_clause
+from synapse.storage.database import (
+    DatabasePool,
+    LoggingDatabaseConnection,
+    LoggingTransaction,
+    make_in_list_sql_clause,
+)
 from synapse.storage.databases.main.stream import generate_pagination_where_clause
 from synapse.storage.relations import (
     AggregationPaginationToken,
@@ -29,10 +45,24 @@ from synapse.storage.relations import (
 )
 from synapse.util.caches.descriptors import cached
 
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
 logger = logging.getLogger(__name__)
 
 
 class RelationsWorkerStore(SQLBaseStore):
+    def __init__(
+        self,
+        database: DatabasePool,
+        db_conn: LoggingDatabaseConnection,
+        hs: "HomeServer",
+    ):
+        super().__init__(database, db_conn, hs)
+
+        self._msc1849_enabled = hs.config.experimental.msc1849_enabled
+        self._msc3440_enabled = hs.config.experimental.msc3440_enabled
+
     @cached(tree=True)
     async def get_relations_for_event(
         self,
@@ -354,8 +384,7 @@ class RelationsWorkerStore(SQLBaseStore):
     async def get_thread_summary(
         self, event_id: str, room_id: str
     ) -> Tuple[int, Optional[EventBase]]:
-        """Get the number of threaded replies, the senders of those replies, and
-        the latest reply (if any) for the given event.
+        """Get the number of threaded replies and the latest reply (if any) for the given event.
 
         Args:
             event_id: Summarize the thread related to this event ID.
@@ -368,7 +397,7 @@ class RelationsWorkerStore(SQLBaseStore):
         def _get_thread_summary_txn(
             txn: LoggingTransaction,
         ) -> Tuple[int, Optional[str]]:
-            # Fetch the count of threaded events and the latest event ID.
+            # Fetch the latest event ID in the thread.
             # TODO Should this only allow m.room.message events.
             sql = """
                 SELECT event_id
@@ -389,6 +418,7 @@ class RelationsWorkerStore(SQLBaseStore):
 
             latest_event_id = row[0]
 
+            # Fetch the number of threaded replies.
             sql = """
                 SELECT COUNT(event_id)
                 FROM event_relations
@@ -413,6 +443,44 @@ class RelationsWorkerStore(SQLBaseStore):
 
         return count, latest_event
 
+    @cached()
+    async def get_thread_participated(
+        self, event_id: str, room_id: str, user_id: str
+    ) -> bool:
+        """Get whether the requesting user participated in a thread.
+
+        This is separate from get_thread_summary since that can be cached across
+        all users while this value is specific to the requeser.
+
+        Args:
+            event_id: The thread related to this event ID.
+            room_id: The room the event belongs to.
+            user_id: The user requesting the summary.
+
+        Returns:
+            True if the requesting user participated in the thread, otherwise false.
+        """
+
+        def _get_thread_summary_txn(txn: LoggingTransaction) -> bool:
+            # Fetch whether the requester has participated or not.
+            sql = """
+                SELECT 1
+                FROM event_relations
+                INNER JOIN events USING (event_id)
+                WHERE
+                    relates_to_id = ?
+                    AND room_id = ?
+                    AND relation_type = ?
+                    AND sender = ?
+            """
+
+            txn.execute(sql, (event_id, room_id, RelationTypes.THREAD, user_id))
+            return bool(txn.fetchone())
+
+        return await self.db_pool.runInteraction(
+            "get_thread_summary", _get_thread_summary_txn
+        )
+
     async def events_have_relations(
         self,
         parent_ids: List[str],
@@ -515,6 +583,104 @@ class RelationsWorkerStore(SQLBaseStore):
             "get_if_user_has_annotated_event", _get_if_user_has_annotated_event
         )
 
+    async def _get_bundled_aggregation_for_event(
+        self, event: EventBase, user_id: str
+    ) -> Optional[Dict[str, Any]]:
+        """Generate bundled aggregations for an event.
+
+        Note that this does not use a cache, but depends on cached methods.
+
+        Args:
+            event: The event to calculate bundled aggregations for.
+            user_id: The user requesting the bundled aggregations.
+
+        Returns:
+            The bundled aggregations for an event, if bundled aggregations are
+            enabled and the event can have bundled aggregations.
+        """
+        # State events and redacted events do not get bundled aggregations.
+        if event.is_state() or event.internal_metadata.is_redacted():
+            return None
+
+        # Do not bundle aggregations for an event which represents an edit or an
+        # annotation. It does not make sense for them to have related events.
+        relates_to = event.content.get("m.relates_to")
+        if isinstance(relates_to, (dict, frozendict)):
+            relation_type = relates_to.get("rel_type")
+            if relation_type in (RelationTypes.ANNOTATION, RelationTypes.REPLACE):
+                return None
+
+        event_id = event.event_id
+        room_id = event.room_id
+
+        # The bundled aggregations to include, a mapping of relation type to a
+        # type-specific value. Some types include the direct return type here
+        # while others need more processing during serialization.
+        aggregations: Dict[str, Any] = {}
+
+        annotations = await self.get_aggregation_groups_for_event(event_id, room_id)
+        if annotations.chunk:
+            aggregations[RelationTypes.ANNOTATION] = annotations.to_dict()
+
+        references = await self.get_relations_for_event(
+            event_id, room_id, RelationTypes.REFERENCE, direction="f"
+        )
+        if references.chunk:
+            aggregations[RelationTypes.REFERENCE] = references.to_dict()
+
+        edit = None
+        if event.type == EventTypes.Message:
+            edit = await self.get_applicable_edit(event_id, room_id)
+
+        if edit:
+            aggregations[RelationTypes.REPLACE] = edit
+
+        # If this event is the start of a thread, include a summary of the replies.
+        if self._msc3440_enabled:
+            thread_count, latest_thread_event = await self.get_thread_summary(
+                event_id, room_id
+            )
+            participated = await self.get_thread_participated(
+                event_id, room_id, user_id
+            )
+            if latest_thread_event:
+                aggregations[RelationTypes.THREAD] = {
+                    "latest_event": latest_thread_event,
+                    "count": thread_count,
+                    "current_user_participated": participated,
+                }
+
+        # Store the bundled aggregations in the event metadata for later use.
+        return aggregations
+
+    async def get_bundled_aggregations(
+        self,
+        events: Iterable[EventBase],
+        user_id: str,
+    ) -> Dict[str, Dict[str, Any]]:
+        """Generate bundled aggregations for events.
+
+        Args:
+            events: The iterable of events to calculate bundled aggregations for.
+            user_id: The user requesting the bundled aggregations.
+
+        Returns:
+            A map of event ID to the bundled aggregation for the event. Not all
+            events may have bundled aggregations in the results.
+        """
+        # If bundled aggregations are disabled, nothing to do.
+        if not self._msc1849_enabled:
+            return {}
+
+        # TODO Parallelize.
+        results = {}
+        for event in events:
+            event_result = await self._get_bundled_aggregation_for_event(event, user_id)
+            if event_result is not None:
+                results[event.event_id] = event_result
+
+        return results
+
 
 class RelationsStore(RelationsWorkerStore):
     pass
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index c0e837854a..95167116c9 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -551,24 +551,24 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
             FROM room_stats_state state
             INNER JOIN room_stats_current curr USING (room_id)
             INNER JOIN rooms USING (room_id)
-            %s
-            ORDER BY %s %s
+            {where}
+            ORDER BY {order_by} {direction}, state.room_id {direction}
             LIMIT ?
             OFFSET ?
-        """ % (
-            where_statement,
-            order_by_column,
-            "ASC" if order_by_asc else "DESC",
+        """.format(
+            where=where_statement,
+            order_by=order_by_column,
+            direction="ASC" if order_by_asc else "DESC",
         )
 
         # Use a nested SELECT statement as SQL can't count(*) with an OFFSET
         count_sql = """
             SELECT count(*) FROM (
               SELECT room_id FROM room_stats_state state
-              %s
+              {where}
             ) AS get_room_ids
-        """ % (
-            where_statement,
+        """.format(
+            where=where_statement,
         )
 
         def _get_rooms_paginate_txn(
diff --git a/synapse/storage/databases/main/roommember.py b/synapse/storage/databases/main/roommember.py
index cda80d6511..4489732fda 100644
--- a/synapse/storage/databases/main/roommember.py
+++ b/synapse/storage/databases/main/roommember.py
@@ -1177,18 +1177,18 @@ class RoomMemberStore(RoomMemberWorkerStore, RoomMemberBackgroundUpdateStore):
         await self.db_pool.runInteraction("forget_membership", f)
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _JoinedHostsCache:
     """The cached data used by the `_get_joined_hosts_cache`."""
 
     # Dict of host to the set of their users in the room at the state group.
-    hosts_to_joined_users = attr.ib(type=Dict[str, Set[str]], factory=dict)
+    hosts_to_joined_users: Dict[str, Set[str]] = attr.Factory(dict)
 
     # The state group `hosts_to_joined_users` is derived from. Will be an object
     # if the instance is newly created or if the state is not based on a state
     # group. (An object is used as a sentinel value to ensure that it never is
     # equal to anything else).
-    state_group = attr.ib(type=Union[object, int], factory=object)
+    state_group: Union[object, int] = attr.Factory(object)
 
     def __len__(self):
         return sum(len(v) for v in self.hosts_to_joined_users.values())
diff --git a/synapse/storage/databases/main/session.py b/synapse/storage/databases/main/session.py
index 5a97120437..e8c776b97a 100644
--- a/synapse/storage/databases/main/session.py
+++ b/synapse/storage/databases/main/session.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 #  Copyright 2021 The Matrix.org Foundation C.I.C.
 #
 #  Licensed under the Apache License, Version 2.0 (the "License");
diff --git a/synapse/storage/databases/main/transactions.py b/synapse/storage/databases/main/transactions.py
index 6c299cafa5..4b78b4d098 100644
--- a/synapse/storage/databases/main/transactions.py
+++ b/synapse/storage/databases/main/transactions.py
@@ -560,3 +560,14 @@ class TransactionWorkerStore(CacheInvalidationWorkerStore):
         return await self.db_pool.runInteraction(
             "get_destinations_paginate_txn", get_destinations_paginate_txn
         )
+
+    async def is_destination_known(self, destination: str) -> bool:
+        """Check if a destination is known to the server."""
+        result = await self.db_pool.simple_select_one_onecol(
+            table="destinations",
+            keyvalues={"destination": destination},
+            retcol="1",
+            allow_none=True,
+            desc="is_destination_known",
+        )
+        return bool(result)
diff --git a/synapse/storage/databases/main/ui_auth.py b/synapse/storage/databases/main/ui_auth.py
index a1a1a6a14a..2d339b6008 100644
--- a/synapse/storage/databases/main/ui_auth.py
+++ b/synapse/storage/databases/main/ui_auth.py
@@ -23,19 +23,19 @@ from synapse.types import JsonDict
 from synapse.util import json_encoder, stringutils
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class UIAuthSessionData:
-    session_id = attr.ib(type=str)
+    session_id: str
     # The dictionary from the client root level, not the 'auth' key.
-    clientdict = attr.ib(type=JsonDict)
+    clientdict: JsonDict
     # The URI and method the session was intiatied with. These are checked at
     # each stage of the authentication to ensure that the asked for operation
     # has not changed.
-    uri = attr.ib(type=str)
-    method = attr.ib(type=str)
+    uri: str
+    method: str
     # A string description of the operation that the current authentication is
     # authorising.
-    description = attr.ib(type=str)
+    description: str
 
 
 class UIAuthWorkerStore(SQLBaseStore):
diff --git a/synapse/storage/databases/main/user_directory.py b/synapse/storage/databases/main/user_directory.py
index 0f9b8575d3..f7c778bdf2 100644
--- a/synapse/storage/databases/main/user_directory.py
+++ b/synapse/storage/databases/main/user_directory.py
@@ -105,8 +105,10 @@ class UserDirectoryBackgroundUpdateStore(StateDeltasStore):
                 GROUP BY room_id
             """
             txn.execute(sql)
-            rooms = [{"room_id": x[0], "events": x[1]} for x in txn.fetchall()]
-            self.db_pool.simple_insert_many_txn(txn, TEMP_TABLE + "_rooms", rooms)
+            rooms = list(txn.fetchall())
+            self.db_pool.simple_insert_many_txn(
+                txn, TEMP_TABLE + "_rooms", keys=("room_id", "events"), values=rooms
+            )
             del rooms
 
             sql = (
@@ -117,9 +119,11 @@ class UserDirectoryBackgroundUpdateStore(StateDeltasStore):
             txn.execute(sql)
 
             txn.execute("SELECT name FROM users")
-            users = [{"user_id": x[0]} for x in txn.fetchall()]
+            users = list(txn.fetchall())
 
-            self.db_pool.simple_insert_many_txn(txn, TEMP_TABLE + "_users", users)
+            self.db_pool.simple_insert_many_txn(
+                txn, TEMP_TABLE + "_users", keys=("user_id",), values=users
+            )
 
         new_pos = await self.get_max_stream_id_in_current_state_deltas()
         await self.db_pool.runInteraction(
diff --git a/synapse/storage/databases/state/bg_updates.py b/synapse/storage/databases/state/bg_updates.py
index eb1118d2cb..5de70f31d2 100644
--- a/synapse/storage/databases/state/bg_updates.py
+++ b/synapse/storage/databases/state/bg_updates.py
@@ -327,14 +327,15 @@ class StateBackgroundUpdateStore(StateGroupBackgroundUpdateStore):
                         self.db_pool.simple_insert_many_txn(
                             txn,
                             table="state_groups_state",
+                            keys=(
+                                "state_group",
+                                "room_id",
+                                "type",
+                                "state_key",
+                                "event_id",
+                            ),
                             values=[
-                                {
-                                    "state_group": state_group,
-                                    "room_id": room_id,
-                                    "type": key[0],
-                                    "state_key": key[1],
-                                    "event_id": state_id,
-                                }
+                                (state_group, room_id, key[0], key[1], state_id)
                                 for key, state_id in delta_state.items()
                             ],
                         )
diff --git a/synapse/storage/databases/state/store.py b/synapse/storage/databases/state/store.py
index c4c8c0021b..7614d76ac6 100644
--- a/synapse/storage/databases/state/store.py
+++ b/synapse/storage/databases/state/store.py
@@ -460,14 +460,9 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
                 self.db_pool.simple_insert_many_txn(
                     txn,
                     table="state_groups_state",
+                    keys=("state_group", "room_id", "type", "state_key", "event_id"),
                     values=[
-                        {
-                            "state_group": state_group,
-                            "room_id": room_id,
-                            "type": key[0],
-                            "state_key": key[1],
-                            "event_id": state_id,
-                        }
+                        (state_group, room_id, key[0], key[1], state_id)
                         for key, state_id in delta_ids.items()
                     ],
                 )
@@ -475,14 +470,9 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
                 self.db_pool.simple_insert_many_txn(
                     txn,
                     table="state_groups_state",
+                    keys=("state_group", "room_id", "type", "state_key", "event_id"),
                     values=[
-                        {
-                            "state_group": state_group,
-                            "room_id": room_id,
-                            "type": key[0],
-                            "state_key": key[1],
-                            "event_id": state_id,
-                        }
+                        (state_group, room_id, key[0], key[1], state_id)
                         for key, state_id in current_state_ids.items()
                     ],
                 )
@@ -589,14 +579,9 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
             self.db_pool.simple_insert_many_txn(
                 txn,
                 table="state_groups_state",
+                keys=("state_group", "room_id", "type", "state_key", "event_id"),
                 values=[
-                    {
-                        "state_group": sg,
-                        "room_id": room_id,
-                        "type": key[0],
-                        "state_key": key[1],
-                        "event_id": state_id,
-                    }
+                    (sg, room_id, key[0], key[1], state_id)
                     for key, state_id in curr_state.items()
                 ],
             )
diff --git a/synapse/storage/keys.py b/synapse/storage/keys.py
index 540adb8781..71584f3f74 100644
--- a/synapse/storage/keys.py
+++ b/synapse/storage/keys.py
@@ -21,7 +21,7 @@ from signedjson.types import VerifyKey
 logger = logging.getLogger(__name__)
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class FetchKeyResult:
-    verify_key = attr.ib(type=VerifyKey)  # the key itself
-    valid_until_ts = attr.ib(type=int)  # how long we can use this key for
+    verify_key: VerifyKey  # the key itself
+    valid_until_ts: int  # how long we can use this key for
diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index e45adfcb55..1823e18720 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -696,7 +696,7 @@ def _get_or_create_schema_state(
     )
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _DirectoryListing:
     """Helper class to store schema file name and the
     absolute path to it.
@@ -705,5 +705,5 @@ class _DirectoryListing:
     `file_name` attr is kept first.
     """
 
-    file_name = attr.ib(type=str)
-    absolute_path = attr.ib(type=str)
+    file_name: str
+    absolute_path: str
diff --git a/synapse/storage/relations.py b/synapse/storage/relations.py
index 10a46b5e82..b1536c1ca4 100644
--- a/synapse/storage/relations.py
+++ b/synapse/storage/relations.py
@@ -23,7 +23,7 @@ from synapse.types import JsonDict
 logger = logging.getLogger(__name__)
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class PaginationChunk:
     """Returned by relation pagination APIs.
 
@@ -35,9 +35,9 @@ class PaginationChunk:
             None then there are no previous results.
     """
 
-    chunk = attr.ib(type=List[JsonDict])
-    next_batch = attr.ib(type=Optional[Any], default=None)
-    prev_batch = attr.ib(type=Optional[Any], default=None)
+    chunk: List[JsonDict]
+    next_batch: Optional[Any] = None
+    prev_batch: Optional[Any] = None
 
     def to_dict(self) -> Dict[str, Any]:
         d = {"chunk": self.chunk}
@@ -51,7 +51,7 @@ class PaginationChunk:
         return d
 
 
-@attr.s(frozen=True, slots=True)
+@attr.s(frozen=True, slots=True, auto_attribs=True)
 class RelationPaginationToken:
     """Pagination token for relation pagination API.
 
@@ -64,8 +64,8 @@ class RelationPaginationToken:
         stream: The stream ordering of the boundary event.
     """
 
-    topological = attr.ib(type=int)
-    stream = attr.ib(type=int)
+    topological: int
+    stream: int
 
     @staticmethod
     def from_string(string: str) -> "RelationPaginationToken":
@@ -82,7 +82,7 @@ class RelationPaginationToken:
         return attr.astuple(self)
 
 
-@attr.s(frozen=True, slots=True)
+@attr.s(frozen=True, slots=True, auto_attribs=True)
 class AggregationPaginationToken:
     """Pagination token for relation aggregation pagination API.
 
@@ -94,8 +94,8 @@ class AggregationPaginationToken:
         stream: The MAX stream ordering in the boundary group.
     """
 
-    count = attr.ib(type=int)
-    stream = attr.ib(type=int)
+    count: int
+    stream: int
 
     @staticmethod
     def from_string(string: str) -> "AggregationPaginationToken":
diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index b5ba1560d1..df8b2f1088 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -45,7 +45,7 @@ logger = logging.getLogger(__name__)
 T = TypeVar("T")
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class StateFilter:
     """A filter used when querying for state.
 
@@ -58,8 +58,8 @@ class StateFilter:
             appear in `types`.
     """
 
-    types = attr.ib(type="frozendict[str, Optional[FrozenSet[str]]]")
-    include_others = attr.ib(default=False, type=bool)
+    types: "frozendict[str, Optional[FrozenSet[str]]]"
+    include_others: bool = False
 
     def __attrs_post_init__(self):
         # If `include_others` is set we canonicalise the filter by removing
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index b8112e1c05..3c13859faa 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -762,13 +762,13 @@ class _AsyncCtxManagerWrapper(Generic[T]):
         return self.inner.__exit__(exc_type, exc, tb)
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _MultiWriterCtxManager:
     """Async context manager returned by MultiWriterIdGenerator"""
 
-    id_gen = attr.ib(type=MultiWriterIdGenerator)
-    multiple_ids = attr.ib(type=Optional[int], default=None)
-    stream_ids = attr.ib(type=List[int], factory=list)
+    id_gen: MultiWriterIdGenerator
+    multiple_ids: Optional[int] = None
+    stream_ids: List[int] = attr.Factory(list)
 
     async def __aenter__(self) -> Union[int, List[int]]:
         # It's safe to run this in autocommit mode as fetching values from a
diff --git a/synapse/streams/config.py b/synapse/streams/config.py
index c08d591f29..b52723e2b8 100644
--- a/synapse/streams/config.py
+++ b/synapse/streams/config.py
@@ -28,14 +28,14 @@ logger = logging.getLogger(__name__)
 MAX_LIMIT = 1000
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class PaginationConfig:
     """A configuration object which stores pagination parameters."""
 
-    from_token = attr.ib(type=Optional[StreamToken])
-    to_token = attr.ib(type=Optional[StreamToken])
-    direction = attr.ib(type=str)
-    limit = attr.ib(type=Optional[int])
+    from_token: Optional[StreamToken]
+    to_token: Optional[StreamToken]
+    direction: str
+    limit: Optional[int]
 
     @classmethod
     async def from_request(
diff --git a/synapse/types.py b/synapse/types.py
index 42aeaf6270..f89fb216a6 100644
--- a/synapse/types.py
+++ b/synapse/types.py
@@ -20,7 +20,9 @@ from typing import (
     Any,
     ClassVar,
     Dict,
+    List,
     Mapping,
+    Match,
     MutableMapping,
     Optional,
     Tuple,
@@ -79,7 +81,7 @@ class ISynapseReactor(
     """The interfaces necessary for Synapse to function."""
 
 
-@attr.s(frozen=True, slots=True)
+@attr.s(frozen=True, slots=True, auto_attribs=True)
 class Requester:
     """
     Represents the user making a request
@@ -97,13 +99,13 @@ class Requester:
             "puppeting" the user.
     """
 
-    user = attr.ib(type="UserID")
-    access_token_id = attr.ib(type=Optional[int])
-    is_guest = attr.ib(type=bool)
-    shadow_banned = attr.ib(type=bool)
-    device_id = attr.ib(type=Optional[str])
-    app_service = attr.ib(type=Optional["ApplicationService"])
-    authenticated_entity = attr.ib(type=str)
+    user: "UserID"
+    access_token_id: Optional[int]
+    is_guest: bool
+    shadow_banned: bool
+    device_id: Optional[str]
+    app_service: Optional["ApplicationService"]
+    authenticated_entity: str
 
     def serialize(self):
         """Converts self to a type that can be serialized as JSON, and then
@@ -210,7 +212,7 @@ def get_localpart_from_id(string: str) -> str:
 DS = TypeVar("DS", bound="DomainSpecificString")
 
 
-@attr.s(slots=True, frozen=True, repr=False)
+@attr.s(slots=True, frozen=True, repr=False, auto_attribs=True)
 class DomainSpecificString(metaclass=abc.ABCMeta):
     """Common base class among ID/name strings that have a local part and a
     domain name, prefixed with a sigil.
@@ -223,8 +225,8 @@ class DomainSpecificString(metaclass=abc.ABCMeta):
 
     SIGIL: ClassVar[str] = abc.abstractproperty()  # type: ignore
 
-    localpart = attr.ib(type=str)
-    domain = attr.ib(type=str)
+    localpart: str
+    domain: str
 
     # Because this is a frozen class, it is deeply immutable.
     def __copy__(self):
@@ -380,7 +382,7 @@ def map_username_to_mxid_localpart(
             onto different mxids
 
     Returns:
-        unicode: string suitable for a mxid localpart
+        string suitable for a mxid localpart
     """
     if not isinstance(username, bytes):
         username = username.encode("utf-8")
@@ -388,29 +390,23 @@ def map_username_to_mxid_localpart(
     # first we sort out upper-case characters
     if case_sensitive:
 
-        def f1(m):
+        def f1(m: Match[bytes]) -> bytes:
             return b"_" + m.group().lower()
 
         username = UPPER_CASE_PATTERN.sub(f1, username)
     else:
         username = username.lower()
 
-    # then we sort out non-ascii characters
-    def f2(m):
-        g = m.group()[0]
-        if isinstance(g, str):
-            # on python 2, we need to do a ord(). On python 3, the
-            # byte itself will do.
-            g = ord(g)
-        return b"=%02x" % (g,)
+    # then we sort out non-ascii characters by converting to the hex equivalent.
+    def f2(m: Match[bytes]) -> bytes:
+        return b"=%02x" % (m.group()[0],)
 
     username = NON_MXID_CHARACTER_PATTERN.sub(f2, username)
 
     # we also do the =-escaping to mxids starting with an underscore.
     username = re.sub(b"^_", b"=5f", username)
 
-    # we should now only have ascii bytes left, so can decode back to a
-    # unicode.
+    # we should now only have ascii bytes left, so can decode back to a string.
     return username.decode("ascii")
 
 
@@ -466,14 +462,12 @@ class RoomStreamToken:
     attributes, must be hashable.
     """
 
-    topological = attr.ib(
-        type=Optional[int],
+    topological: Optional[int] = attr.ib(
         validator=attr.validators.optional(attr.validators.instance_of(int)),
     )
-    stream = attr.ib(type=int, validator=attr.validators.instance_of(int))
+    stream: int = attr.ib(validator=attr.validators.instance_of(int))
 
-    instance_map = attr.ib(
-        type="frozendict[str, int]",
+    instance_map: "frozendict[str, int]" = attr.ib(
         factory=frozendict,
         validator=attr.validators.deep_mapping(
             key_validator=attr.validators.instance_of(str),
@@ -482,7 +476,7 @@ class RoomStreamToken:
         ),
     )
 
-    def __attrs_post_init__(self):
+    def __attrs_post_init__(self) -> None:
         """Validates that both `topological` and `instance_map` aren't set."""
 
         if self.instance_map and self.topological:
@@ -598,7 +592,7 @@ class RoomStreamToken:
             return "s%d" % (self.stream,)
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class StreamToken:
     """A collection of positions within multiple streams.
 
@@ -606,20 +600,20 @@ class StreamToken:
     must be hashable.
     """
 
-    room_key = attr.ib(
-        type=RoomStreamToken, validator=attr.validators.instance_of(RoomStreamToken)
+    room_key: RoomStreamToken = attr.ib(
+        validator=attr.validators.instance_of(RoomStreamToken)
     )
-    presence_key = attr.ib(type=int)
-    typing_key = attr.ib(type=int)
-    receipt_key = attr.ib(type=int)
-    account_data_key = attr.ib(type=int)
-    push_rules_key = attr.ib(type=int)
-    to_device_key = attr.ib(type=int)
-    device_list_key = attr.ib(type=int)
-    groups_key = attr.ib(type=int)
+    presence_key: int
+    typing_key: int
+    receipt_key: int
+    account_data_key: int
+    push_rules_key: int
+    to_device_key: int
+    device_list_key: int
+    groups_key: int
 
     _SEPARATOR = "_"
-    START: "StreamToken"
+    START: ClassVar["StreamToken"]
 
     @classmethod
     async def from_string(cls, store: "DataStore", string: str) -> "StreamToken":
@@ -679,7 +673,7 @@ class StreamToken:
 StreamToken.START = StreamToken(RoomStreamToken(None, 0), 0, 0, 0, 0, 0, 0, 0, 0)
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class PersistedEventPosition:
     """Position of a newly persisted event with instance that persisted it.
 
@@ -687,8 +681,8 @@ class PersistedEventPosition:
     RoomStreamToken.
     """
 
-    instance_name = attr.ib(type=str)
-    stream = attr.ib(type=int)
+    instance_name: str
+    stream: int
 
     def persisted_after(self, token: RoomStreamToken) -> bool:
         return token.get_stream_pos_for_instance(self.instance_name) < self.stream
@@ -738,15 +732,15 @@ class ThirdPartyInstanceID:
     __str__ = to_string
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class ReadReceipt:
     """Information about a read-receipt"""
 
-    room_id = attr.ib()
-    receipt_type = attr.ib()
-    user_id = attr.ib()
-    event_ids = attr.ib()
-    data = attr.ib()
+    room_id: str
+    receipt_type: str
+    user_id: str
+    event_ids: List[str]
+    data: JsonDict
 
 
 def get_verify_key_from_cross_signing_key(key_info):
diff --git a/synapse/util/async_helpers.py b/synapse/util/async_helpers.py
index 150a04b53e..3f7299aff7 100644
--- a/synapse/util/async_helpers.py
+++ b/synapse/util/async_helpers.py
@@ -309,12 +309,12 @@ def gather_results(  # type: ignore[misc]
     return deferred.addCallback(tuple)
 
 
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class _LinearizerEntry:
     # The number of things executing.
-    count = attr.ib(type=int)
+    count: int
     # Deferreds for the things blocked from executing.
-    deferreds = attr.ib(type=collections.OrderedDict)
+    deferreds: collections.OrderedDict
 
 
 class Linearizer:
diff --git a/synapse/util/caches/dictionary_cache.py b/synapse/util/caches/dictionary_cache.py
index 485ddb1893..d267703df0 100644
--- a/synapse/util/caches/dictionary_cache.py
+++ b/synapse/util/caches/dictionary_cache.py
@@ -33,7 +33,7 @@ DV = TypeVar("DV")
 
 # This class can't be generic because it uses slots with attrs.
 # See: https://github.com/python-attrs/attrs/issues/313
-@attr.s(slots=True)
+@attr.s(slots=True, auto_attribs=True)
 class DictionaryEntry:  # should be: Generic[DKT, DV].
     """Returned when getting an entry from the cache
 
@@ -41,14 +41,13 @@ class DictionaryEntry:  # should be: Generic[DKT, DV].
         full: Whether the cache has the full or dict or just some keys.
             If not full then not all requested keys will necessarily be present
             in `value`
-        known_absent: Keys that were looked up in the dict and were not
-            there.
+        known_absent: Keys that were looked up in the dict and were not there.
         value: The full or partial dict value
     """
 
-    full = attr.ib(type=bool)
-    known_absent = attr.ib(type=Set[Any])  # should be: Set[DKT]
-    value = attr.ib(type=Dict[Any, Any])  # should be: Dict[DKT, DV]
+    full: bool
+    known_absent: Set[Any]  # should be: Set[DKT]
+    value: Dict[Any, Any]  # should be: Dict[DKT, DV]
 
     def __len__(self) -> int:
         return len(self.value)