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authorEric Eastwood <erice@element.io>2021-11-11 00:56:50 -0600
committerEric Eastwood <erice@element.io>2021-11-11 00:56:50 -0600
commitb559e2326b419b71bdbcf88ab35a6f3fbbea8219 (patch)
treee3ef5d870af0ee1888a88201f888933dd9e1a2b4 /synapse
parentOnly run the tests package to get streaming Complement output (diff)
parentFix typos in the `username_available` admin API documentation. (#11286) (diff)
downloadsynapse-b559e2326b419b71bdbcf88ab35a6f3fbbea8219.tar.xz
Merge branch 'develop' into madlittlemods/return-historical-events-in-order-from-backfill
Conflicts:
	synapse/rest/client/room_batch.py
Diffstat (limited to 'synapse')
-rw-r--r--synapse/api/filtering.py115
-rw-r--r--synapse/api/urls.py3
-rw-r--r--synapse/config/account_validity.py4
-rw-r--r--synapse/config/cas.py10
-rw-r--r--synapse/config/emailconfig.py8
-rw-r--r--synapse/config/oidc.py2
-rw-r--r--synapse/config/registration.py15
-rw-r--r--synapse/config/saml2.py5
-rw-r--r--synapse/config/server.py45
-rw-r--r--synapse/config/sso.py18
-rw-r--r--synapse/config/workers.py18
-rw-r--r--synapse/federation/federation_client.py80
-rw-r--r--synapse/federation/federation_server.py9
-rw-r--r--synapse/handlers/appservice.py93
-rw-r--r--synapse/handlers/auth.py4
-rw-r--r--synapse/handlers/devicemessage.py31
-rw-r--r--synapse/handlers/e2e_keys.py211
-rw-r--r--synapse/handlers/identity.py4
-rw-r--r--synapse/handlers/pagination.py2
-rw-r--r--synapse/handlers/room.py59
-rw-r--r--synapse/handlers/search.py8
-rw-r--r--synapse/handlers/sync.py18
-rw-r--r--synapse/handlers/typing.py6
-rw-r--r--synapse/replication/tcp/handler.py2
-rw-r--r--synapse/replication/tcp/streams/_base.py3
-rw-r--r--synapse/rest/admin/__init__.py6
-rw-r--r--synapse/rest/admin/background_updates.py107
-rw-r--r--synapse/rest/admin/rooms.py26
-rw-r--r--synapse/rest/client/receipts.py12
-rw-r--r--synapse/rest/client/relations.py4
-rw-r--r--synapse/rest/client/room.py12
-rw-r--r--synapse/rest/client/room_batch.py29
-rw-r--r--synapse/rest/client/sync.py6
-rw-r--r--synapse/rest/well_known.py3
-rw-r--r--synapse/server.py4
-rw-r--r--synapse/storage/background_updates.py65
-rw-r--r--synapse/storage/database.py4
-rw-r--r--synapse/storage/databases/main/appservice.py8
-rw-r--r--synapse/storage/databases/main/deviceinbox.py23
-rw-r--r--synapse/storage/databases/main/events_worker.py56
-rw-r--r--synapse/storage/databases/main/lock.py31
-rw-r--r--synapse/storage/databases/main/relations.py58
-rw-r--r--synapse/storage/databases/main/room.py7
-rw-r--r--synapse/storage/databases/main/stream.py86
-rw-r--r--synapse/storage/prepare_database.py23
45 files changed, 956 insertions, 387 deletions
diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index 4b0a9b2974..13dd6ce248 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -1,7 +1,7 @@
 # Copyright 2015, 2016 OpenMarket Ltd
 # Copyright 2017 Vector Creations Ltd
 # Copyright 2018-2019 New Vector Ltd
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2019-2021 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.
@@ -86,6 +86,9 @@ ROOM_EVENT_FILTER_SCHEMA = {
         # cf https://github.com/matrix-org/matrix-doc/pull/2326
         "org.matrix.labels": {"type": "array", "items": {"type": "string"}},
         "org.matrix.not_labels": {"type": "array", "items": {"type": "string"}},
+        # MSC3440, filtering by event relations.
+        "io.element.relation_senders": {"type": "array", "items": {"type": "string"}},
+        "io.element.relation_types": {"type": "array", "items": {"type": "string"}},
     },
 }
 
@@ -146,14 +149,16 @@ def matrix_user_id_validator(user_id_str: str) -> UserID:
 
 class Filtering:
     def __init__(self, hs: "HomeServer"):
-        super().__init__()
+        self._hs = hs
         self.store = hs.get_datastore()
 
+        self.DEFAULT_FILTER_COLLECTION = FilterCollection(hs, {})
+
     async def get_user_filter(
         self, user_localpart: str, filter_id: Union[int, str]
     ) -> "FilterCollection":
         result = await self.store.get_user_filter(user_localpart, filter_id)
-        return FilterCollection(result)
+        return FilterCollection(self._hs, result)
 
     def add_user_filter(
         self, user_localpart: str, user_filter: JsonDict
@@ -191,21 +196,22 @@ FilterEvent = TypeVar("FilterEvent", EventBase, UserPresenceState, JsonDict)
 
 
 class FilterCollection:
-    def __init__(self, filter_json: JsonDict):
+    def __init__(self, hs: "HomeServer", filter_json: JsonDict):
         self._filter_json = filter_json
 
         room_filter_json = self._filter_json.get("room", {})
 
         self._room_filter = Filter(
-            {k: v for k, v in room_filter_json.items() if k in ("rooms", "not_rooms")}
+            hs,
+            {k: v for k, v in room_filter_json.items() if k in ("rooms", "not_rooms")},
         )
 
-        self._room_timeline_filter = Filter(room_filter_json.get("timeline", {}))
-        self._room_state_filter = Filter(room_filter_json.get("state", {}))
-        self._room_ephemeral_filter = Filter(room_filter_json.get("ephemeral", {}))
-        self._room_account_data = Filter(room_filter_json.get("account_data", {}))
-        self._presence_filter = Filter(filter_json.get("presence", {}))
-        self._account_data = Filter(filter_json.get("account_data", {}))
+        self._room_timeline_filter = Filter(hs, room_filter_json.get("timeline", {}))
+        self._room_state_filter = Filter(hs, room_filter_json.get("state", {}))
+        self._room_ephemeral_filter = Filter(hs, room_filter_json.get("ephemeral", {}))
+        self._room_account_data = Filter(hs, room_filter_json.get("account_data", {}))
+        self._presence_filter = Filter(hs, filter_json.get("presence", {}))
+        self._account_data = Filter(hs, filter_json.get("account_data", {}))
 
         self.include_leave = filter_json.get("room", {}).get("include_leave", False)
         self.event_fields = filter_json.get("event_fields", [])
@@ -232,25 +238,37 @@ class FilterCollection:
     def include_redundant_members(self) -> bool:
         return self._room_state_filter.include_redundant_members
 
-    def filter_presence(
+    async def filter_presence(
         self, events: Iterable[UserPresenceState]
     ) -> List[UserPresenceState]:
-        return self._presence_filter.filter(events)
+        return await self._presence_filter.filter(events)
 
-    def filter_account_data(self, events: Iterable[JsonDict]) -> List[JsonDict]:
-        return self._account_data.filter(events)
+    async def filter_account_data(self, events: Iterable[JsonDict]) -> List[JsonDict]:
+        return await self._account_data.filter(events)
 
-    def filter_room_state(self, events: Iterable[EventBase]) -> List[EventBase]:
-        return self._room_state_filter.filter(self._room_filter.filter(events))
+    async def filter_room_state(self, events: Iterable[EventBase]) -> List[EventBase]:
+        return await self._room_state_filter.filter(
+            await self._room_filter.filter(events)
+        )
 
-    def filter_room_timeline(self, events: Iterable[EventBase]) -> List[EventBase]:
-        return self._room_timeline_filter.filter(self._room_filter.filter(events))
+    async def filter_room_timeline(
+        self, events: Iterable[EventBase]
+    ) -> List[EventBase]:
+        return await self._room_timeline_filter.filter(
+            await self._room_filter.filter(events)
+        )
 
-    def filter_room_ephemeral(self, events: Iterable[JsonDict]) -> List[JsonDict]:
-        return self._room_ephemeral_filter.filter(self._room_filter.filter(events))
+    async def filter_room_ephemeral(self, events: Iterable[JsonDict]) -> List[JsonDict]:
+        return await self._room_ephemeral_filter.filter(
+            await self._room_filter.filter(events)
+        )
 
-    def filter_room_account_data(self, events: Iterable[JsonDict]) -> List[JsonDict]:
-        return self._room_account_data.filter(self._room_filter.filter(events))
+    async def filter_room_account_data(
+        self, events: Iterable[JsonDict]
+    ) -> List[JsonDict]:
+        return await self._room_account_data.filter(
+            await self._room_filter.filter(events)
+        )
 
     def blocks_all_presence(self) -> bool:
         return (
@@ -274,7 +292,9 @@ class FilterCollection:
 
 
 class Filter:
-    def __init__(self, filter_json: JsonDict):
+    def __init__(self, hs: "HomeServer", filter_json: JsonDict):
+        self._hs = hs
+        self._store = hs.get_datastore()
         self.filter_json = filter_json
 
         self.limit = filter_json.get("limit", 10)
@@ -297,6 +317,20 @@ class Filter:
         self.labels = filter_json.get("org.matrix.labels", None)
         self.not_labels = filter_json.get("org.matrix.not_labels", [])
 
+        # Ideally these would be rejected at the endpoint if they were provided
+        # and not supported, but that would involve modifying the JSON schema
+        # based on the homeserver configuration.
+        if hs.config.experimental.msc3440_enabled:
+            self.relation_senders = self.filter_json.get(
+                "io.element.relation_senders", None
+            )
+            self.relation_types = self.filter_json.get(
+                "io.element.relation_types", None
+            )
+        else:
+            self.relation_senders = None
+            self.relation_types = None
+
     def filters_all_types(self) -> bool:
         return "*" in self.not_types
 
@@ -306,7 +340,7 @@ class Filter:
     def filters_all_rooms(self) -> bool:
         return "*" in self.not_rooms
 
-    def check(self, event: FilterEvent) -> bool:
+    def _check(self, event: FilterEvent) -> bool:
         """Checks whether the filter matches the given event.
 
         Args:
@@ -420,8 +454,30 @@ class Filter:
 
         return room_ids
 
-    def filter(self, events: Iterable[FilterEvent]) -> List[FilterEvent]:
-        return list(filter(self.check, events))
+    async def _check_event_relations(
+        self, events: Iterable[FilterEvent]
+    ) -> List[FilterEvent]:
+        # The event IDs to check, mypy doesn't understand the ifinstance check.
+        event_ids = [event.event_id for event in events if isinstance(event, EventBase)]  # type: ignore[attr-defined]
+        event_ids_to_keep = set(
+            await self._store.events_have_relations(
+                event_ids, self.relation_senders, self.relation_types
+            )
+        )
+
+        return [
+            event
+            for event in events
+            if not isinstance(event, EventBase) or event.event_id in event_ids_to_keep
+        ]
+
+    async def filter(self, events: Iterable[FilterEvent]) -> List[FilterEvent]:
+        result = [event for event in events if self._check(event)]
+
+        if self.relation_senders or self.relation_types:
+            return await self._check_event_relations(result)
+
+        return result
 
     def with_room_ids(self, room_ids: Iterable[str]) -> "Filter":
         """Returns a new filter with the given room IDs appended.
@@ -433,7 +489,7 @@ class Filter:
             filter: A new filter including the given rooms and the old
                     filter's rooms.
         """
-        newFilter = Filter(self.filter_json)
+        newFilter = Filter(self._hs, self.filter_json)
         newFilter.rooms += room_ids
         return newFilter
 
@@ -444,6 +500,3 @@ def _matches_wildcard(actual_value: Optional[str], filter_value: str) -> bool:
         return actual_value.startswith(type_prefix)
     else:
         return actual_value == filter_value
-
-
-DEFAULT_FILTER_COLLECTION = FilterCollection({})
diff --git a/synapse/api/urls.py b/synapse/api/urls.py
index 6e84b1524f..4486b3bc7d 100644
--- a/synapse/api/urls.py
+++ b/synapse/api/urls.py
@@ -38,9 +38,6 @@ class ConsentURIBuilder:
     def __init__(self, hs_config: HomeServerConfig):
         if hs_config.key.form_secret is None:
             raise ConfigError("form_secret not set in config")
-        if hs_config.server.public_baseurl is None:
-            raise ConfigError("public_baseurl not set in config")
-
         self._hmac_secret = hs_config.key.form_secret.encode("utf-8")
         self._public_baseurl = hs_config.server.public_baseurl
 
diff --git a/synapse/config/account_validity.py b/synapse/config/account_validity.py
index b56c2a24df..c533452cab 100644
--- a/synapse/config/account_validity.py
+++ b/synapse/config/account_validity.py
@@ -75,10 +75,6 @@ class AccountValidityConfig(Config):
                 self.account_validity_period * 10.0 / 100.0
             )
 
-        if self.account_validity_renew_by_email_enabled:
-            if not self.root.server.public_baseurl:
-                raise ConfigError("Can't send renewal emails without 'public_baseurl'")
-
         # Load account validity templates.
         account_validity_template_dir = account_validity_config.get("template_dir")
         if account_validity_template_dir is not None:
diff --git a/synapse/config/cas.py b/synapse/config/cas.py
index 9b58ecf3d8..3f81814043 100644
--- a/synapse/config/cas.py
+++ b/synapse/config/cas.py
@@ -16,7 +16,7 @@ from typing import Any, List
 
 from synapse.config.sso import SsoAttributeRequirement
 
-from ._base import Config, ConfigError
+from ._base import Config
 from ._util import validate_config
 
 
@@ -35,14 +35,10 @@ class CasConfig(Config):
         if self.cas_enabled:
             self.cas_server_url = cas_config["server_url"]
 
-            # The public baseurl is required because it is used by the redirect
-            # template.
-            public_baseurl = self.root.server.public_baseurl
-            if not public_baseurl:
-                raise ConfigError("cas_config requires a public_baseurl to be set")
-
             # TODO Update this to a _synapse URL.
+            public_baseurl = self.root.server.public_baseurl
             self.cas_service_url = public_baseurl + "_matrix/client/r0/login/cas/ticket"
+
             self.cas_displayname_attribute = cas_config.get("displayname_attribute")
             required_attributes = cas_config.get("required_attributes") or {}
             self.cas_required_attributes = _parsed_required_attributes_def(
diff --git a/synapse/config/emailconfig.py b/synapse/config/emailconfig.py
index 8ff59aa2f8..afd65fecd3 100644
--- a/synapse/config/emailconfig.py
+++ b/synapse/config/emailconfig.py
@@ -186,11 +186,6 @@ class EmailConfig(Config):
             if not self.email_notif_from:
                 missing.append("email.notif_from")
 
-            # public_baseurl is required to build password reset and validation links that
-            # will be emailed to users
-            if config.get("public_baseurl") is None:
-                missing.append("public_baseurl")
-
             if missing:
                 raise ConfigError(
                     MISSING_PASSWORD_RESET_CONFIG_ERROR % (", ".join(missing),)
@@ -296,9 +291,6 @@ class EmailConfig(Config):
             if not self.email_notif_from:
                 missing.append("email.notif_from")
 
-            if config.get("public_baseurl") is None:
-                missing.append("public_baseurl")
-
             if missing:
                 raise ConfigError(
                     "email.enable_notifs is True but required keys are missing: %s"
diff --git a/synapse/config/oidc.py b/synapse/config/oidc.py
index 10f5796330..42f113cd24 100644
--- a/synapse/config/oidc.py
+++ b/synapse/config/oidc.py
@@ -59,8 +59,6 @@ class OIDCConfig(Config):
                 )
 
         public_baseurl = self.root.server.public_baseurl
-        if public_baseurl is None:
-            raise ConfigError("oidc_config requires a public_baseurl to be set")
         self.oidc_callback_url = public_baseurl + "_synapse/client/oidc/callback"
 
     @property
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index a3d2a38c4c..5379e80715 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -45,17 +45,6 @@ class RegistrationConfig(Config):
         account_threepid_delegates = config.get("account_threepid_delegates") or {}
         self.account_threepid_delegate_email = account_threepid_delegates.get("email")
         self.account_threepid_delegate_msisdn = account_threepid_delegates.get("msisdn")
-        if (
-            self.account_threepid_delegate_msisdn
-            and not self.root.server.public_baseurl
-        ):
-            raise ConfigError(
-                "The configuration option `public_baseurl` is required if "
-                "`account_threepid_delegate.msisdn` is set, such that "
-                "clients know where to submit validation tokens to. Please "
-                "configure `public_baseurl`."
-            )
-
         self.default_identity_server = config.get("default_identity_server")
         self.allow_guest_access = config.get("allow_guest_access", False)
 
@@ -240,7 +229,7 @@ class RegistrationConfig(Config):
         # in on this server.
         #
         # (By default, no suggestion is made, so it is left up to the client.
-        # This setting is ignored unless public_baseurl is also set.)
+        # This setting is ignored unless public_baseurl is also explicitly set.)
         #
         #default_identity_server: https://matrix.org
 
@@ -265,8 +254,6 @@ class RegistrationConfig(Config):
         # by the Matrix Identity Service API specification:
         # https://matrix.org/docs/spec/identity_service/latest
         #
-        # If a delegate is specified, the config option public_baseurl must also be filled out.
-        #
         account_threepid_delegates:
             #email: https://example.com     # Delegate email sending to example.com
             #msisdn: http://localhost:8090  # Delegate SMS sending to this local process
diff --git a/synapse/config/saml2.py b/synapse/config/saml2.py
index 9c51b6a25a..ba2b0905ff 100644
--- a/synapse/config/saml2.py
+++ b/synapse/config/saml2.py
@@ -199,14 +199,11 @@ class SAML2Config(Config):
         """
         import saml2
 
-        public_baseurl = self.root.server.public_baseurl
-        if public_baseurl is None:
-            raise ConfigError("saml2_config requires a public_baseurl to be set")
-
         if self.saml2_grandfathered_mxid_source_attribute:
             optional_attributes.add(self.saml2_grandfathered_mxid_source_attribute)
         optional_attributes -= required_attributes
 
+        public_baseurl = self.root.server.public_baseurl
         metadata_url = public_baseurl + "_synapse/client/saml2/metadata.xml"
         response_url = public_baseurl + "_synapse/client/saml2/authn_response"
         return {
diff --git a/synapse/config/server.py b/synapse/config/server.py
index a387fd9310..7bc0030a9e 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -16,6 +16,7 @@ import itertools
 import logging
 import os.path
 import re
+import urllib.parse
 from textwrap import indent
 from typing import Any, Dict, Iterable, List, Optional, Set, Tuple, Union
 
@@ -264,10 +265,44 @@ class ServerConfig(Config):
         self.use_frozen_dicts = config.get("use_frozen_dicts", False)
         self.serve_server_wellknown = config.get("serve_server_wellknown", False)
 
-        self.public_baseurl = config.get("public_baseurl")
-        if self.public_baseurl is not None:
-            if self.public_baseurl[-1] != "/":
-                self.public_baseurl += "/"
+        # Whether we should serve a "client well-known":
+        #  (a) at .well-known/matrix/client on our client HTTP listener
+        #  (b) in the response to /login
+        #
+        # ... which together help ensure that clients use our public_baseurl instead of
+        # whatever they were told by the user.
+        #
+        # For the sake of backwards compatibility with existing installations, this is
+        # True if public_baseurl is specified explicitly, and otherwise False. (The
+        # reasoning here is that we have no way of knowing that the default
+        # public_baseurl is actually correct for existing installations - many things
+        # will not work correctly, but that's (probably?) better than sending clients
+        # to a completely broken URL.
+        self.serve_client_wellknown = False
+
+        public_baseurl = config.get("public_baseurl")
+        if public_baseurl is None:
+            public_baseurl = f"https://{self.server_name}/"
+            logger.info("Using default public_baseurl %s", public_baseurl)
+        else:
+            self.serve_client_wellknown = True
+            if public_baseurl[-1] != "/":
+                public_baseurl += "/"
+        self.public_baseurl = public_baseurl
+
+        # check that public_baseurl is valid
+        try:
+            splits = urllib.parse.urlsplit(self.public_baseurl)
+        except Exception as e:
+            raise ConfigError(f"Unable to parse URL: {e}", ("public_baseurl",))
+        if splits.scheme not in ("https", "http"):
+            raise ConfigError(
+                f"Invalid scheme '{splits.scheme}': only https and http are supported"
+            )
+        if splits.query or splits.fragment:
+            raise ConfigError(
+                "public_baseurl cannot contain query parameters or a #-fragment"
+            )
 
         # Whether to enable user presence.
         presence_config = config.get("presence") or {}
@@ -773,6 +808,8 @@ class ServerConfig(Config):
         # Otherwise, it should be the URL to reach Synapse's client HTTP listener (see
         # 'listeners' below).
         #
+        # Defaults to 'https://<server_name>/'.
+        #
         #public_baseurl: https://example.com/
 
         # Uncomment the following to tell other servers to send federation traffic on
diff --git a/synapse/config/sso.py b/synapse/config/sso.py
index 11a9b76aa0..60aacb13ea 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -101,13 +101,10 @@ class SSOConfig(Config):
         # gracefully to the client). This would make it pointless to ask the user for
         # confirmation, since the URL the confirmation page would be showing wouldn't be
         # the client's.
-        # public_baseurl is an optional setting, so we only add the fallback's URL to the
-        # list if it's provided (because we can't figure out what that URL is otherwise).
-        if self.root.server.public_baseurl:
-            login_fallback_url = (
-                self.root.server.public_baseurl + "_matrix/static/client/login"
-            )
-            self.sso_client_whitelist.append(login_fallback_url)
+        login_fallback_url = (
+            self.root.server.public_baseurl + "_matrix/static/client/login"
+        )
+        self.sso_client_whitelist.append(login_fallback_url)
 
     def generate_config_section(self, **kwargs):
         return """\
@@ -128,11 +125,10 @@ class SSOConfig(Config):
             # phishing attacks from evil.site. To avoid this, include a slash after the
             # hostname: "https://my.client/".
             #
-            # If public_baseurl is set, then the login fallback page (used by clients
-            # that don't natively support the required login flows) is whitelisted in
-            # addition to any URLs in this list.
+            # The login fallback page (used by clients that don't natively support the
+            # required login flows) is whitelisted in addition to any URLs in this list.
             #
-            # By default, this list is empty.
+            # By default, this list contains only the login fallback page.
             #
             #client_whitelist:
             #  - https://riot.im/develop
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index 462630201d..4507992031 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -63,7 +63,8 @@ class WriterLocations:
 
     Attributes:
         events: The instances that write to the event and backfill streams.
-        typing: The instance that writes to the typing stream.
+        typing: The instances that write to the typing stream. Currently
+            can only be a single instance.
         to_device: The instances that write to the to_device stream. Currently
             can only be a single instance.
         account_data: The instances that write to the account data streams. Currently
@@ -75,9 +76,15 @@ class WriterLocations:
     """
 
     events = attr.ib(
-        default=["master"], type=List[str], converter=_instance_to_list_converter
+        default=["master"],
+        type=List[str],
+        converter=_instance_to_list_converter,
+    )
+    typing = attr.ib(
+        default=["master"],
+        type=List[str],
+        converter=_instance_to_list_converter,
     )
-    typing = attr.ib(default="master", type=str)
     to_device = attr.ib(
         default=["master"],
         type=List[str],
@@ -217,6 +224,11 @@ class WorkerConfig(Config):
                         % (instance, stream)
                     )
 
+        if len(self.writers.typing) != 1:
+            raise ConfigError(
+                "Must only specify one instance to handle `typing` messages."
+            )
+
         if len(self.writers.to_device) != 1:
             raise ConfigError(
                 "Must only specify one instance to handle `to_device` messages."
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 670186f548..3b85b135e0 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -277,6 +277,58 @@ class FederationClient(FederationBase):
 
         return pdus
 
+    async def get_pdu_from_destination_raw(
+        self,
+        destination: str,
+        event_id: str,
+        room_version: RoomVersion,
+        outlier: bool = False,
+        timeout: Optional[int] = None,
+    ) -> Optional[EventBase]:
+        """Requests the PDU with given origin and ID from the remote home
+        server. Does not have any caching or rate limiting!
+
+        Args:
+            destination: Which homeserver to query
+            event_id: event to fetch
+            room_version: version of the room
+            outlier: Indicates whether the PDU is an `outlier`, i.e. if
+                it's from an arbitrary point in the context as opposed to part
+                of the current block of PDUs. Defaults to `False`
+            timeout: How long to try (in ms) each destination for before
+                moving to the next destination. None indicates no timeout.
+
+        Returns:
+            The requested PDU, or None if we were unable to find it.
+
+        Raises:
+            SynapseError, NotRetryingDestination, FederationDeniedError
+        """
+        transaction_data = await self.transport_layer.get_event(
+            destination, event_id, timeout=timeout
+        )
+
+        logger.debug(
+            "retrieved event id %s from %s: %r",
+            event_id,
+            destination,
+            transaction_data,
+        )
+
+        pdu_list: List[EventBase] = [
+            event_from_pdu_json(p, room_version, outlier=outlier)
+            for p in transaction_data["pdus"]
+        ]
+
+        if pdu_list and pdu_list[0]:
+            pdu = pdu_list[0]
+
+            # Check signatures are correct.
+            signed_pdu = await self._check_sigs_and_hash(room_version, pdu)
+            return signed_pdu
+
+        return None
+
     async def get_pdu(
         self,
         destinations: Iterable[str],
@@ -321,30 +373,14 @@ class FederationClient(FederationBase):
                 continue
 
             try:
-                transaction_data = await self.transport_layer.get_event(
-                    destination, event_id, timeout=timeout
-                )
-
-                logger.debug(
-                    "retrieved event id %s from %s: %r",
-                    event_id,
-                    destination,
-                    transaction_data,
+                signed_pdu = await self.get_pdu_from_destination_raw(
+                    destination=destination,
+                    event_id=event_id,
+                    room_version=room_version,
+                    outlier=outlier,
+                    timeout=timeout,
                 )
 
-                pdu_list: List[EventBase] = [
-                    event_from_pdu_json(p, room_version, outlier=outlier)
-                    for p in transaction_data["pdus"]
-                ]
-
-                if pdu_list and pdu_list[0]:
-                    pdu = pdu_list[0]
-
-                    # Check signatures are correct.
-                    signed_pdu = await self._check_sigs_and_hash(room_version, pdu)
-
-                    break
-
                 pdu_attempts[destination] = now
 
             except SynapseError as e:
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 32a75993d9..9a8758e9a6 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -213,6 +213,11 @@ class FederationServer(FederationBase):
             self._started_handling_of_staged_events = True
             self._handle_old_staged_events()
 
+            # Start a periodic check for old staged events. This is to handle
+            # the case where locks time out, e.g. if another process gets killed
+            # without dropping its locks.
+            self._clock.looping_call(self._handle_old_staged_events, 60 * 1000)
+
         # keep this as early as possible to make the calculated origin ts as
         # accurate as possible.
         request_time = self._clock.time_msec()
@@ -1232,10 +1237,6 @@ class FederationHandlerRegistry:
 
         self.query_handlers[query_type] = handler
 
-    def register_instance_for_edu(self, edu_type: str, instance_name: str) -> None:
-        """Register that the EDU handler is on a different instance than master."""
-        self._edu_type_to_instance[edu_type] = [instance_name]
-
     def register_instances_for_edu(
         self, edu_type: str, instance_names: List[str]
     ) -> None:
diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index 67f8ffcaff..9abdad262b 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -34,6 +34,7 @@ from synapse.metrics.background_process_metrics import (
 )
 from synapse.storage.databases.main.directory import RoomAliasMapping
 from synapse.types import JsonDict, RoomAlias, RoomStreamToken, UserID
+from synapse.util.async_helpers import Linearizer
 from synapse.util.metrics import Measure
 
 if TYPE_CHECKING:
@@ -58,6 +59,10 @@ class ApplicationServicesHandler:
         self.current_max = 0
         self.is_processing = False
 
+        self._ephemeral_events_linearizer = Linearizer(
+            name="appservice_ephemeral_events"
+        )
+
     def notify_interested_services(self, max_token: RoomStreamToken) -> None:
         """Notifies (pushes) all application services interested in this event.
 
@@ -183,7 +188,7 @@ class ApplicationServicesHandler:
         self,
         stream_key: str,
         new_token: Union[int, RoomStreamToken],
-        users: Optional[Collection[Union[str, UserID]]] = None,
+        users: Collection[Union[str, UserID]],
     ) -> None:
         """
         This is called by the notifier in the background when an ephemeral event is handled
@@ -198,7 +203,9 @@ class ApplicationServicesHandler:
                 value for `stream_key` will cause this function to return early.
 
                 Ephemeral events will only be pushed to appservices that have opted into
-                them.
+                receiving them by setting `push_ephemeral` to true in their registration
+                file. Note that while MSC2409 is experimental, this option is called
+                `de.sorunome.msc2409.push_ephemeral`.
 
                 Appservices will only receive ephemeral events that fall within their
                 registered user and room namespaces.
@@ -209,6 +216,7 @@ class ApplicationServicesHandler:
         if not self.notify_appservices:
             return
 
+        # Ignore any unsupported streams
         if stream_key not in ("typing_key", "receipt_key", "presence_key"):
             return
 
@@ -225,18 +233,25 @@ class ApplicationServicesHandler:
         # Additional context: https://github.com/matrix-org/synapse/pull/11137
         assert isinstance(new_token, int)
 
+        # Check whether there are any appservices which have registered to receive
+        # ephemeral events.
+        #
+        # Note that whether these events are actually relevant to these appservices
+        # is decided later on.
         services = [
             service
             for service in self.store.get_app_services()
             if service.supports_ephemeral
         ]
         if not services:
+            # Bail out early if none of the target appservices have explicitly registered
+            # to receive these ephemeral events.
             return
 
         # We only start a new background process if necessary rather than
         # optimistically (to cut down on overhead).
         self._notify_interested_services_ephemeral(
-            services, stream_key, new_token, users or []
+            services, stream_key, new_token, users
         )
 
     @wrap_as_background_process("notify_interested_services_ephemeral")
@@ -247,7 +262,7 @@ class ApplicationServicesHandler:
         new_token: int,
         users: Collection[Union[str, UserID]],
     ) -> None:
-        logger.debug("Checking interested services for %s" % (stream_key))
+        logger.debug("Checking interested services for %s", stream_key)
         with Measure(self.clock, "notify_interested_services_ephemeral"):
             for service in services:
                 if stream_key == "typing_key":
@@ -260,26 +275,37 @@ class ApplicationServicesHandler:
                     events = await self._handle_typing(service, new_token)
                     if events:
                         self.scheduler.submit_ephemeral_events_for_as(service, events)
+                    continue
 
-                elif stream_key == "receipt_key":
-                    events = await self._handle_receipts(service)
-                    if events:
-                        self.scheduler.submit_ephemeral_events_for_as(service, events)
-
-                    # Persist the latest handled stream token for this appservice
-                    await self.store.set_type_stream_id_for_appservice(
-                        service, "read_receipt", new_token
+                # Since we read/update the stream position for this AS/stream
+                with (
+                    await self._ephemeral_events_linearizer.queue(
+                        (service.id, stream_key)
                     )
+                ):
+                    if stream_key == "receipt_key":
+                        events = await self._handle_receipts(service, new_token)
+                        if events:
+                            self.scheduler.submit_ephemeral_events_for_as(
+                                service, events
+                            )
+
+                        # Persist the latest handled stream token for this appservice
+                        await self.store.set_type_stream_id_for_appservice(
+                            service, "read_receipt", new_token
+                        )
 
-                elif stream_key == "presence_key":
-                    events = await self._handle_presence(service, users)
-                    if events:
-                        self.scheduler.submit_ephemeral_events_for_as(service, events)
+                    elif stream_key == "presence_key":
+                        events = await self._handle_presence(service, users, new_token)
+                        if events:
+                            self.scheduler.submit_ephemeral_events_for_as(
+                                service, events
+                            )
 
-                    # Persist the latest handled stream token for this appservice
-                    await self.store.set_type_stream_id_for_appservice(
-                        service, "presence", new_token
-                    )
+                        # Persist the latest handled stream token for this appservice
+                        await self.store.set_type_stream_id_for_appservice(
+                            service, "presence", new_token
+                        )
 
     async def _handle_typing(
         self, service: ApplicationService, new_token: int
@@ -316,7 +342,9 @@ class ApplicationServicesHandler:
         )
         return typing
 
-    async def _handle_receipts(self, service: ApplicationService) -> List[JsonDict]:
+    async def _handle_receipts(
+        self, service: ApplicationService, new_token: Optional[int]
+    ) -> List[JsonDict]:
         """
         Return the latest read receipts that the given application service should receive.
 
@@ -327,6 +355,9 @@ class ApplicationServicesHandler:
 
         Args:
             service: The application service to check for which events it should receive.
+            new_token: A receipts event stream token. Purely used to double-check that the
+                from_token we pull from the database isn't greater than or equal to this
+                token. Prevents accidentally duplicating work.
 
         Returns:
             A list of JSON dictionaries containing data derived from the read receipts that
@@ -335,6 +366,12 @@ class ApplicationServicesHandler:
         from_key = await self.store.get_type_stream_id_for_appservice(
             service, "read_receipt"
         )
+        if new_token is not None and new_token <= from_key:
+            logger.debug(
+                "Rejecting token lower than or equal to stored: %s" % (new_token,)
+            )
+            return []
+
         receipts_source = self.event_sources.sources.receipt
         receipts, _ = await receipts_source.get_new_events_as(
             service=service, from_key=from_key
@@ -342,7 +379,10 @@ class ApplicationServicesHandler:
         return receipts
 
     async def _handle_presence(
-        self, service: ApplicationService, users: Collection[Union[str, UserID]]
+        self,
+        service: ApplicationService,
+        users: Collection[Union[str, UserID]],
+        new_token: Optional[int],
     ) -> List[JsonDict]:
         """
         Return the latest presence updates that the given application service should receive.
@@ -355,6 +395,9 @@ class ApplicationServicesHandler:
         Args:
             service: The application service that ephemeral events are being sent to.
             users: The users that should receive the presence update.
+            new_token: A presence update stream token. Purely used to double-check that the
+                from_token we pull from the database isn't greater than or equal to this
+                token. Prevents accidentally duplicating work.
 
         Returns:
             A list of json dictionaries containing data derived from the presence events
@@ -365,6 +408,12 @@ class ApplicationServicesHandler:
         from_key = await self.store.get_type_stream_id_for_appservice(
             service, "presence"
         )
+        if new_token is not None and new_token <= from_key:
+            logger.debug(
+                "Rejecting token lower than or equal to stored: %s" % (new_token,)
+            )
+            return []
+
         for user in users:
             if isinstance(user, str):
                 user = UserID.from_string(user)
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index d508d7d32a..60e59d11a0 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -1989,7 +1989,9 @@ class PasswordAuthProvider:
         self,
         check_3pid_auth: Optional[CHECK_3PID_AUTH_CALLBACK] = None,
         on_logged_out: Optional[ON_LOGGED_OUT_CALLBACK] = None,
-        auth_checkers: Optional[Dict[Tuple[str, Tuple], CHECK_AUTH_CALLBACK]] = None,
+        auth_checkers: Optional[
+            Dict[Tuple[str, Tuple[str, ...]], CHECK_AUTH_CALLBACK]
+        ] = None,
     ) -> None:
         # Register check_3pid_auth callback
         if check_3pid_auth is not None:
diff --git a/synapse/handlers/devicemessage.py b/synapse/handlers/devicemessage.py
index b6a2a34ab7..b582266af9 100644
--- a/synapse/handlers/devicemessage.py
+++ b/synapse/handlers/devicemessage.py
@@ -89,6 +89,13 @@ class DeviceMessageHandler:
         )
 
     async def on_direct_to_device_edu(self, origin: str, content: JsonDict) -> None:
+        """
+        Handle receiving to-device messages from remote homeservers.
+
+        Args:
+            origin: The remote homeserver.
+            content: The JSON dictionary containing the to-device messages.
+        """
         local_messages = {}
         sender_user_id = content["sender"]
         if origin != get_domain_from_id(sender_user_id):
@@ -135,12 +142,16 @@ class DeviceMessageHandler:
                 message_type, sender_user_id, by_device
             )
 
-        stream_id = await self.store.add_messages_from_remote_to_device_inbox(
+        # Add messages to the database.
+        # Retrieve the stream id of the last-processed to-device message.
+        last_stream_id = await self.store.add_messages_from_remote_to_device_inbox(
             origin, message_id, local_messages
         )
 
+        # Notify listeners that there are new to-device messages to process,
+        # handing them the latest stream id.
         self.notifier.on_new_event(
-            "to_device_key", stream_id, users=local_messages.keys()
+            "to_device_key", last_stream_id, users=local_messages.keys()
         )
 
     async def _check_for_unknown_devices(
@@ -195,6 +206,14 @@ class DeviceMessageHandler:
         message_type: str,
         messages: Dict[str, Dict[str, JsonDict]],
     ) -> None:
+        """
+        Handle a request from a user to send to-device message(s).
+
+        Args:
+            requester: The user that is sending the to-device messages.
+            message_type: The type of to-device messages that are being sent.
+            messages: A dictionary containing recipients mapped to messages intended for them.
+        """
         sender_user_id = requester.user.to_string()
 
         message_id = random_string(16)
@@ -257,12 +276,16 @@ class DeviceMessageHandler:
                 "org.matrix.opentracing_context": json_encoder.encode(context),
             }
 
-        stream_id = await self.store.add_messages_to_device_inbox(
+        # Add messages to the database.
+        # Retrieve the stream id of the last-processed to-device message.
+        last_stream_id = await self.store.add_messages_to_device_inbox(
             local_messages, remote_edu_contents
         )
 
+        # Notify listeners that there are new to-device messages to process,
+        # handing them the latest stream id.
         self.notifier.on_new_event(
-            "to_device_key", stream_id, users=local_messages.keys()
+            "to_device_key", last_stream_id, users=local_messages.keys()
         )
 
         if self.federation_sender:
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index d0fb2fc7dc..60c11e3d21 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -201,95 +201,19 @@ class E2eKeysHandler:
                     r[user_id] = remote_queries[user_id]
 
             # Now fetch any devices that we don't have in our cache
-            @trace
-            async def do_remote_query(destination: str) -> None:
-                """This is called when we are querying the device list of a user on
-                a remote homeserver and their device list is not in the device list
-                cache. If we share a room with this user and we're not querying for
-                specific user we will update the cache with their device list.
-                """
-
-                destination_query = remote_queries_not_in_cache[destination]
-
-                # We first consider whether we wish to update the device list cache with
-                # the users device list. We want to track a user's devices when the
-                # authenticated user shares a room with the queried user and the query
-                # has not specified a particular device.
-                # If we update the cache for the queried user we remove them from further
-                # queries. We use the more efficient batched query_client_keys for all
-                # remaining users
-                user_ids_updated = []
-                for (user_id, device_list) in destination_query.items():
-                    if user_id in user_ids_updated:
-                        continue
-
-                    if device_list:
-                        continue
-
-                    room_ids = await self.store.get_rooms_for_user(user_id)
-                    if not room_ids:
-                        continue
-
-                    # We've decided we're sharing a room with this user and should
-                    # probably be tracking their device lists. However, we haven't
-                    # done an initial sync on the device list so we do it now.
-                    try:
-                        if self._is_master:
-                            user_devices = await self.device_handler.device_list_updater.user_device_resync(
-                                user_id
-                            )
-                        else:
-                            user_devices = await self._user_device_resync_client(
-                                user_id=user_id
-                            )
-
-                        user_devices = user_devices["devices"]
-                        user_results = results.setdefault(user_id, {})
-                        for device in user_devices:
-                            user_results[device["device_id"]] = device["keys"]
-                        user_ids_updated.append(user_id)
-                    except Exception as e:
-                        failures[destination] = _exception_to_failure(e)
-
-                if len(destination_query) == len(user_ids_updated):
-                    # We've updated all the users in the query and we do not need to
-                    # make any further remote calls.
-                    return
-
-                # Remove all the users from the query which we have updated
-                for user_id in user_ids_updated:
-                    destination_query.pop(user_id)
-
-                try:
-                    remote_result = await self.federation.query_client_keys(
-                        destination, {"device_keys": destination_query}, timeout=timeout
-                    )
-
-                    for user_id, keys in remote_result["device_keys"].items():
-                        if user_id in destination_query:
-                            results[user_id] = keys
-
-                    if "master_keys" in remote_result:
-                        for user_id, key in remote_result["master_keys"].items():
-                            if user_id in destination_query:
-                                cross_signing_keys["master_keys"][user_id] = key
-
-                    if "self_signing_keys" in remote_result:
-                        for user_id, key in remote_result["self_signing_keys"].items():
-                            if user_id in destination_query:
-                                cross_signing_keys["self_signing_keys"][user_id] = key
-
-                except Exception as e:
-                    failure = _exception_to_failure(e)
-                    failures[destination] = failure
-                    set_tag("error", True)
-                    set_tag("reason", failure)
-
             await make_deferred_yieldable(
                 defer.gatherResults(
                     [
-                        run_in_background(do_remote_query, destination)
-                        for destination in remote_queries_not_in_cache
+                        run_in_background(
+                            self._query_devices_for_destination,
+                            results,
+                            cross_signing_keys,
+                            failures,
+                            destination,
+                            queries,
+                            timeout,
+                        )
+                        for destination, queries in remote_queries_not_in_cache.items()
                     ],
                     consumeErrors=True,
                 ).addErrback(unwrapFirstError)
@@ -301,6 +225,121 @@ class E2eKeysHandler:
 
             return ret
 
+    @trace
+    async def _query_devices_for_destination(
+        self,
+        results: JsonDict,
+        cross_signing_keys: JsonDict,
+        failures: Dict[str, JsonDict],
+        destination: str,
+        destination_query: Dict[str, Iterable[str]],
+        timeout: int,
+    ) -> None:
+        """This is called when we are querying the device list of a user on
+        a remote homeserver and their device list is not in the device list
+        cache. If we share a room with this user and we're not querying for
+        specific user we will update the cache with their device list.
+
+        Args:
+            results: A map from user ID to their device keys, which gets
+                updated with the newly fetched keys.
+            cross_signing_keys: Map from user ID to their cross signing keys,
+                which gets updated with the newly fetched keys.
+            failures: Map of destinations to failures that have occurred while
+                attempting to fetch keys.
+            destination: The remote server to query
+            destination_query: The query dict of devices to query the remote
+                server for.
+            timeout: The timeout for remote HTTP requests.
+        """
+
+        # We first consider whether we wish to update the device list cache with
+        # the users device list. We want to track a user's devices when the
+        # authenticated user shares a room with the queried user and the query
+        # has not specified a particular device.
+        # If we update the cache for the queried user we remove them from further
+        # queries. We use the more efficient batched query_client_keys for all
+        # remaining users
+        user_ids_updated = []
+        for (user_id, device_list) in destination_query.items():
+            if user_id in user_ids_updated:
+                continue
+
+            if device_list:
+                continue
+
+            room_ids = await self.store.get_rooms_for_user(user_id)
+            if not room_ids:
+                continue
+
+            # We've decided we're sharing a room with this user and should
+            # probably be tracking their device lists. However, we haven't
+            # done an initial sync on the device list so we do it now.
+            try:
+                if self._is_master:
+                    resync_results = await self.device_handler.device_list_updater.user_device_resync(
+                        user_id
+                    )
+                else:
+                    resync_results = await self._user_device_resync_client(
+                        user_id=user_id
+                    )
+
+                # Add the device keys to the results.
+                user_devices = resync_results["devices"]
+                user_results = results.setdefault(user_id, {})
+                for device in user_devices:
+                    user_results[device["device_id"]] = device["keys"]
+                user_ids_updated.append(user_id)
+
+                # Add any cross signing keys to the results.
+                master_key = resync_results.get("master_key")
+                self_signing_key = resync_results.get("self_signing_key")
+
+                if master_key:
+                    cross_signing_keys["master_keys"][user_id] = master_key
+
+                if self_signing_key:
+                    cross_signing_keys["self_signing_keys"][user_id] = self_signing_key
+            except Exception as e:
+                failures[destination] = _exception_to_failure(e)
+
+        if len(destination_query) == len(user_ids_updated):
+            # We've updated all the users in the query and we do not need to
+            # make any further remote calls.
+            return
+
+        # Remove all the users from the query which we have updated
+        for user_id in user_ids_updated:
+            destination_query.pop(user_id)
+
+        try:
+            remote_result = await self.federation.query_client_keys(
+                destination, {"device_keys": destination_query}, timeout=timeout
+            )
+
+            for user_id, keys in remote_result["device_keys"].items():
+                if user_id in destination_query:
+                    results[user_id] = keys
+
+            if "master_keys" in remote_result:
+                for user_id, key in remote_result["master_keys"].items():
+                    if user_id in destination_query:
+                        cross_signing_keys["master_keys"][user_id] = key
+
+            if "self_signing_keys" in remote_result:
+                for user_id, key in remote_result["self_signing_keys"].items():
+                    if user_id in destination_query:
+                        cross_signing_keys["self_signing_keys"][user_id] = key
+
+        except Exception as e:
+            failure = _exception_to_failure(e)
+            failures[destination] = failure
+            set_tag("error", True)
+            set_tag("reason", failure)
+
+        return
+
     async def get_cross_signing_keys_from_cache(
         self, query: Iterable[str], from_user_id: Optional[str]
     ) -> Dict[str, Dict[str, dict]]:
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py
index 6a315117ba..3dbe611f95 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -537,10 +537,6 @@ class IdentityHandler:
         except RequestTimedOutError:
             raise SynapseError(500, "Timed out contacting identity server")
 
-        # It is already checked that public_baseurl is configured since this code
-        # should only be used if account_threepid_delegate_msisdn is true.
-        assert self.hs.config.server.public_baseurl
-
         # we need to tell the client to send the token back to us, since it doesn't
         # otherwise know where to send it, so add submit_url response parameter
         # (see also MSC2078)
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index abfe7be0e3..aa26911aed 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -424,7 +424,7 @@ class PaginationHandler:
 
         if events:
             if event_filter:
-                events = event_filter.filter(events)
+                events = await event_filter.filter(events)
 
             events = await filter_events_for_client(
                 self.storage, user_id, events, is_peeking=(member_event_id is None)
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 969eb3b9b0..11af30eee7 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -12,8 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Contains functions for performing events on rooms."""
-
+"""Contains functions for performing actions on rooms."""
 import itertools
 import logging
 import math
@@ -31,6 +30,8 @@ from typing import (
     Tuple,
 )
 
+from typing_extensions import TypedDict
+
 from synapse.api.constants import (
     EventContentFields,
     EventTypes,
@@ -1158,8 +1159,10 @@ class RoomContextHandler:
         )
 
         if event_filter:
-            results["events_before"] = event_filter.filter(results["events_before"])
-            results["events_after"] = event_filter.filter(results["events_after"])
+            results["events_before"] = await event_filter.filter(
+                results["events_before"]
+            )
+            results["events_after"] = await event_filter.filter(results["events_after"])
 
         results["events_before"] = await filter_evts(results["events_before"])
         results["events_after"] = await filter_evts(results["events_after"])
@@ -1195,7 +1198,7 @@ class RoomContextHandler:
 
         state_events = list(state[last_event_id].values())
         if event_filter:
-            state_events = event_filter.filter(state_events)
+            state_events = await event_filter.filter(state_events)
 
         results["state"] = await filter_evts(state_events)
 
@@ -1275,6 +1278,13 @@ class RoomEventSource(EventSource[RoomStreamToken, EventBase]):
         return self.store.get_room_events_max_id(room_id)
 
 
+class ShutdownRoomResponse(TypedDict):
+    kicked_users: List[str]
+    failed_to_kick_users: List[str]
+    local_aliases: List[str]
+    new_room_id: Optional[str]
+
+
 class RoomShutdownHandler:
 
     DEFAULT_MESSAGE = (
@@ -1300,7 +1310,7 @@ class RoomShutdownHandler:
         new_room_name: Optional[str] = None,
         message: Optional[str] = None,
         block: bool = False,
-    ) -> dict:
+    ) -> ShutdownRoomResponse:
         """
         Shuts down a room. Moves all local users and room aliases automatically
         to a new room if `new_room_user_id` is set. Otherwise local users only
@@ -1334,8 +1344,13 @@ class RoomShutdownHandler:
                 Defaults to `Sharing illegal content on this server is not
                 permitted and rooms in violation will be blocked.`
             block:
-                If set to `true`, this room will be added to a blocking list,
-                preventing future attempts to join the room. Defaults to `false`.
+                If set to `True`, users will be prevented from joining the old
+                room. This option can also be used to pre-emptively block a room,
+                even if it's unknown to this homeserver. In this case, the room
+                will be blocked, and no further action will be taken. If `False`,
+                attempting to delete an unknown room is invalid.
+
+                Defaults to `False`.
 
         Returns: a dict containing the following keys:
             kicked_users: An array of users (`user_id`) that were kicked.
@@ -1344,7 +1359,9 @@ class RoomShutdownHandler:
             local_aliases:
                 An array of strings representing the local aliases that were
                 migrated from the old room to the new.
-            new_room_id: A string representing the room ID of the new room.
+            new_room_id:
+                A string representing the room ID of the new room, or None if
+                no such room was created.
         """
 
         if not new_room_name:
@@ -1355,14 +1372,28 @@ class RoomShutdownHandler:
         if not RoomID.is_valid(room_id):
             raise SynapseError(400, "%s is not a legal room ID" % (room_id,))
 
-        if not await self.store.get_room(room_id):
-            raise NotFoundError("Unknown room id %s" % (room_id,))
-
-        # This will work even if the room is already blocked, but that is
-        # desirable in case the first attempt at blocking the room failed below.
+        # Action the block first (even if the room doesn't exist yet)
         if block:
+            # This will work even if the room is already blocked, but that is
+            # desirable in case the first attempt at blocking the room failed below.
             await self.store.block_room(room_id, requester_user_id)
 
+        if not await self.store.get_room(room_id):
+            if block:
+                # We allow you to block an unknown room.
+                return {
+                    "kicked_users": [],
+                    "failed_to_kick_users": [],
+                    "local_aliases": [],
+                    "new_room_id": None,
+                }
+            else:
+                # But if you don't want to preventatively block another room,
+                # this function can't do anything useful.
+                raise NotFoundError(
+                    "Cannot shut down room: unknown room id %s" % (room_id,)
+                )
+
         if new_room_user_id is not None:
             if not self.hs.is_mine_id(new_room_user_id):
                 raise SynapseError(
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 6e4dff8056..ab7eaab2fb 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -180,7 +180,7 @@ class SearchHandler:
                 % (set(group_keys) - {"room_id", "sender"},),
             )
 
-        search_filter = Filter(filter_dict)
+        search_filter = Filter(self.hs, filter_dict)
 
         # TODO: Search through left rooms too
         rooms = await self.store.get_rooms_for_local_user_where_membership_is(
@@ -242,7 +242,7 @@ class SearchHandler:
 
             rank_map.update({r["event"].event_id: r["rank"] for r in results})
 
-            filtered_events = search_filter.filter([r["event"] for r in results])
+            filtered_events = await search_filter.filter([r["event"] for r in results])
 
             events = await filter_events_for_client(
                 self.storage, user.to_string(), filtered_events
@@ -292,7 +292,9 @@ class SearchHandler:
 
                 rank_map.update({r["event"].event_id: r["rank"] for r in results})
 
-                filtered_events = search_filter.filter([r["event"] for r in results])
+                filtered_events = await search_filter.filter(
+                    [r["event"] for r in results]
+                )
 
                 events = await filter_events_for_client(
                     self.storage, user.to_string(), filtered_events
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 2c7c6d63a9..891435c14d 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -510,7 +510,7 @@ class SyncHandler:
             log_kv({"limited": limited})
 
             if potential_recents:
-                recents = sync_config.filter_collection.filter_room_timeline(
+                recents = await sync_config.filter_collection.filter_room_timeline(
                     potential_recents
                 )
                 log_kv({"recents_after_sync_filtering": len(recents)})
@@ -575,8 +575,8 @@ class SyncHandler:
 
                 log_kv({"loaded_recents": len(events)})
 
-                loaded_recents = sync_config.filter_collection.filter_room_timeline(
-                    events
+                loaded_recents = (
+                    await sync_config.filter_collection.filter_room_timeline(events)
                 )
 
                 log_kv({"loaded_recents_after_sync_filtering": len(loaded_recents)})
@@ -1015,7 +1015,7 @@ class SyncHandler:
 
         return {
             (e.type, e.state_key): e
-            for e in sync_config.filter_collection.filter_room_state(
+            for e in await sync_config.filter_collection.filter_room_state(
                 list(state.values())
             )
             if e.type != EventTypes.Aliases  # until MSC2261 or alternative solution
@@ -1383,7 +1383,7 @@ class SyncHandler:
                 sync_config.user
             )
 
-        account_data_for_user = sync_config.filter_collection.filter_account_data(
+        account_data_for_user = await sync_config.filter_collection.filter_account_data(
             [
                 {"type": account_data_type, "content": content}
                 for account_data_type, content in account_data.items()
@@ -1448,7 +1448,7 @@ class SyncHandler:
             # Deduplicate the presence entries so that there's at most one per user
             presence = list({p.user_id: p for p in presence}.values())
 
-        presence = sync_config.filter_collection.filter_presence(presence)
+        presence = await sync_config.filter_collection.filter_presence(presence)
 
         sync_result_builder.presence = presence
 
@@ -2021,12 +2021,14 @@ class SyncHandler:
                 )
 
             account_data_events = (
-                sync_config.filter_collection.filter_room_account_data(
+                await sync_config.filter_collection.filter_room_account_data(
                     account_data_events
                 )
             )
 
-            ephemeral = sync_config.filter_collection.filter_room_ephemeral(ephemeral)
+            ephemeral = await sync_config.filter_collection.filter_room_ephemeral(
+                ephemeral
+            )
 
             if not (
                 always_include
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index c411d69924..22c6174821 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -62,8 +62,8 @@ class FollowerTypingHandler:
         if hs.should_send_federation():
             self.federation = hs.get_federation_sender()
 
-        if hs.config.worker.writers.typing != hs.get_instance_name():
-            hs.get_federation_registry().register_instance_for_edu(
+        if hs.get_instance_name() not in hs.config.worker.writers.typing:
+            hs.get_federation_registry().register_instances_for_edu(
                 "m.typing",
                 hs.config.worker.writers.typing,
             )
@@ -205,7 +205,7 @@ class TypingWriterHandler(FollowerTypingHandler):
     def __init__(self, hs: "HomeServer"):
         super().__init__(hs)
 
-        assert hs.config.worker.writers.typing == hs.get_instance_name()
+        assert hs.get_instance_name() in hs.config.worker.writers.typing
 
         self.auth = hs.get_auth()
         self.notifier = hs.get_notifier()
diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index 06fd06fdf3..21293038ef 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -138,7 +138,7 @@ class ReplicationCommandHandler:
             if isinstance(stream, TypingStream):
                 # Only add TypingStream as a source on the instance in charge of
                 # typing.
-                if hs.config.worker.writers.typing == hs.get_instance_name():
+                if hs.get_instance_name() in hs.config.worker.writers.typing:
                     self._streams_to_replicate.append(stream)
 
                 continue
diff --git a/synapse/replication/tcp/streams/_base.py b/synapse/replication/tcp/streams/_base.py
index c8b188ae4e..743a01da08 100644
--- a/synapse/replication/tcp/streams/_base.py
+++ b/synapse/replication/tcp/streams/_base.py
@@ -328,8 +328,7 @@ class TypingStream(Stream):
     ROW_TYPE = TypingStreamRow
 
     def __init__(self, hs: "HomeServer"):
-        writer_instance = hs.config.worker.writers.typing
-        if writer_instance == hs.get_instance_name():
+        if hs.get_instance_name() in hs.config.worker.writers.typing:
             # On the writer, query the typing handler
             typing_writer_handler = hs.get_typing_writer_handler()
             update_function: Callable[
diff --git a/synapse/rest/admin/__init__.py b/synapse/rest/admin/__init__.py
index 70514e814f..81e98f81d6 100644
--- a/synapse/rest/admin/__init__.py
+++ b/synapse/rest/admin/__init__.py
@@ -25,6 +25,10 @@ from synapse.http.server import HttpServer, JsonResource
 from synapse.http.servlet import RestServlet, parse_json_object_from_request
 from synapse.http.site import SynapseRequest
 from synapse.rest.admin._base import admin_patterns, assert_requester_is_admin
+from synapse.rest.admin.background_updates import (
+    BackgroundUpdateEnabledRestServlet,
+    BackgroundUpdateRestServlet,
+)
 from synapse.rest.admin.devices import (
     DeleteDevicesRestServlet,
     DeviceRestServlet,
@@ -247,6 +251,8 @@ def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     # Some servlets only get registered for the main process.
     if hs.config.worker.worker_app is None:
         SendServerNoticeServlet(hs).register(http_server)
+        BackgroundUpdateEnabledRestServlet(hs).register(http_server)
+        BackgroundUpdateRestServlet(hs).register(http_server)
 
 
 def register_servlets_for_client_rest_resource(
diff --git a/synapse/rest/admin/background_updates.py b/synapse/rest/admin/background_updates.py
new file mode 100644
index 0000000000..0d0183bf20
--- /dev/null
+++ b/synapse/rest/admin/background_updates.py
@@ -0,0 +1,107 @@
+# Copyright 2021 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 logging
+from typing import TYPE_CHECKING, Tuple
+
+from synapse.api.errors import SynapseError
+from synapse.http.servlet import RestServlet, parse_json_object_from_request
+from synapse.http.site import SynapseRequest
+from synapse.rest.admin._base import admin_patterns, assert_user_is_admin
+from synapse.types import JsonDict
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class BackgroundUpdateEnabledRestServlet(RestServlet):
+    """Allows temporarily disabling background updates"""
+
+    PATTERNS = admin_patterns("/background_updates/enabled")
+
+    def __init__(self, hs: "HomeServer"):
+        self.group_server = hs.get_groups_server_handler()
+        self.is_mine_id = hs.is_mine_id
+        self.auth = hs.get_auth()
+
+        self.data_stores = hs.get_datastores()
+
+    async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+
+        # We need to check that all configured databases have updates enabled.
+        # (They *should* all be in sync.)
+        enabled = all(db.updates.enabled for db in self.data_stores.databases)
+
+        return 200, {"enabled": enabled}
+
+    async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+
+        body = parse_json_object_from_request(request)
+
+        enabled = body.get("enabled", True)
+
+        if not isinstance(enabled, bool):
+            raise SynapseError(400, "'enabled' parameter must be a boolean")
+
+        for db in self.data_stores.databases:
+            db.updates.enabled = enabled
+
+            # If we're re-enabling them ensure that we start the background
+            # process again.
+            if enabled:
+                db.updates.start_doing_background_updates()
+
+        return 200, {"enabled": enabled}
+
+
+class BackgroundUpdateRestServlet(RestServlet):
+    """Fetch information about background updates"""
+
+    PATTERNS = admin_patterns("/background_updates/status")
+
+    def __init__(self, hs: "HomeServer"):
+        self.group_server = hs.get_groups_server_handler()
+        self.is_mine_id = hs.is_mine_id
+        self.auth = hs.get_auth()
+
+        self.data_stores = hs.get_datastores()
+
+    async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+
+        # We need to check that all configured databases have updates enabled.
+        # (They *should* all be in sync.)
+        enabled = all(db.updates.enabled for db in self.data_stores.databases)
+
+        current_updates = {}
+
+        for db in self.data_stores.databases:
+            update = db.updates.get_current_update()
+            if not update:
+                continue
+
+            current_updates[db.name()] = {
+                "name": update.name,
+                "total_item_count": update.total_item_count,
+                "total_duration_ms": update.total_duration_ms,
+                "average_items_per_ms": update.average_items_per_ms(),
+            }
+
+        return 200, {"enabled": enabled, "current_updates": current_updates}
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 05c5b4bf0c..a2f4edebb8 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -13,7 +13,7 @@
 # limitations under the License.
 import logging
 from http import HTTPStatus
-from typing import TYPE_CHECKING, List, Optional, Tuple
+from typing import TYPE_CHECKING, List, Optional, Tuple, cast
 from urllib import parse as urlparse
 
 from synapse.api.constants import EventTypes, JoinRules, Membership
@@ -239,9 +239,22 @@ class RoomRestServlet(RestServlet):
 
         # Purge room
         if purge:
-            await pagination_handler.purge_room(room_id, force=force_purge)
-
-        return 200, ret
+            try:
+                await pagination_handler.purge_room(room_id, force=force_purge)
+            except NotFoundError:
+                if block:
+                    # We can block unknown rooms with this endpoint, in which case
+                    # a failed purge is expected.
+                    pass
+                else:
+                    # But otherwise, we expect this purge to have succeeded.
+                    raise
+
+        # Cast safety: cast away the knowledge that this is a TypedDict.
+        # See https://github.com/python/mypy/issues/4976#issuecomment-579883622
+        # for some discussion on why this is necessary. Either way,
+        # `ret` is an opaque dictionary blob as far as the rest of the app cares.
+        return 200, cast(JsonDict, ret)
 
 
 class RoomMembersRestServlet(RestServlet):
@@ -583,6 +596,7 @@ class RoomEventContextServlet(RestServlet):
 
     def __init__(self, hs: "HomeServer"):
         super().__init__()
+        self._hs = hs
         self.clock = hs.get_clock()
         self.room_context_handler = hs.get_room_context_handler()
         self._event_serializer = hs.get_event_client_serializer()
@@ -600,7 +614,9 @@ class RoomEventContextServlet(RestServlet):
         filter_str = parse_string(request, "filter", encoding="utf-8")
         if filter_str:
             filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(json_decoder.decode(filter_json))
+            event_filter: Optional[Filter] = Filter(
+                self._hs, json_decoder.decode(filter_json)
+            )
         else:
             event_filter = None
 
diff --git a/synapse/rest/client/receipts.py b/synapse/rest/client/receipts.py
index 9770413c61..2b25b9aad6 100644
--- a/synapse/rest/client/receipts.py
+++ b/synapse/rest/client/receipts.py
@@ -13,10 +13,12 @@
 # limitations under the License.
 
 import logging
+import re
 from typing import TYPE_CHECKING, Tuple
 
 from synapse.api.constants import ReadReceiptEventFields
 from synapse.api.errors import Codes, SynapseError
+from synapse.http import get_request_user_agent
 from synapse.http.server import HttpServer
 from synapse.http.servlet import RestServlet, parse_json_object_from_request
 from synapse.http.site import SynapseRequest
@@ -24,6 +26,8 @@ from synapse.types import JsonDict
 
 from ._base import client_patterns
 
+pattern = re.compile(r"(?:Element|SchildiChat)/1\.[012]\.")
+
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
@@ -52,7 +56,13 @@ class ReceiptRestServlet(RestServlet):
         if receipt_type != "m.read":
             raise SynapseError(400, "Receipt type must be 'm.read'")
 
-        body = parse_json_object_from_request(request, allow_empty_body=True)
+        # Do not allow older SchildiChat and Element Android clients (prior to Element/1.[012].x) to send an empty body.
+        user_agent = get_request_user_agent(request)
+        allow_empty_body = False
+        if "Android" in user_agent:
+            if pattern.match(user_agent) or "Riot" in user_agent:
+                allow_empty_body = True
+        body = parse_json_object_from_request(request, allow_empty_body)
         hidden = body.get(ReadReceiptEventFields.MSC2285_HIDDEN, False)
 
         if not isinstance(hidden, bool):
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index 58f6699073..184cfbe196 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -298,7 +298,9 @@ class RelationAggregationPaginationServlet(RestServlet):
             raise SynapseError(404, "Unknown parent event.")
 
         if relation_type not in (RelationTypes.ANNOTATION, None):
-            raise SynapseError(400, "Relation type must be 'annotation'")
+            raise SynapseError(
+                400, f"Relation type must be '{RelationTypes.ANNOTATION}'"
+            )
 
         limit = parse_integer(request, "limit", default=5)
         from_token_str = parse_string(request, "from")
diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index ed95189b6d..03a353d53c 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -550,6 +550,7 @@ class RoomMessageListRestServlet(RestServlet):
 
     def __init__(self, hs: "HomeServer"):
         super().__init__()
+        self._hs = hs
         self.pagination_handler = hs.get_pagination_handler()
         self.auth = hs.get_auth()
         self.store = hs.get_datastore()
@@ -567,7 +568,9 @@ class RoomMessageListRestServlet(RestServlet):
         filter_str = parse_string(request, "filter", encoding="utf-8")
         if filter_str:
             filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(json_decoder.decode(filter_json))
+            event_filter: Optional[Filter] = Filter(
+                self._hs, json_decoder.decode(filter_json)
+            )
             if (
                 event_filter
                 and event_filter.filter_json.get("event_format", "client")
@@ -672,6 +675,7 @@ class RoomEventContextServlet(RestServlet):
 
     def __init__(self, hs: "HomeServer"):
         super().__init__()
+        self._hs = hs
         self.clock = hs.get_clock()
         self.room_context_handler = hs.get_room_context_handler()
         self._event_serializer = hs.get_event_client_serializer()
@@ -688,7 +692,9 @@ class RoomEventContextServlet(RestServlet):
         filter_str = parse_string(request, "filter", encoding="utf-8")
         if filter_str:
             filter_json = urlparse.unquote(filter_str)
-            event_filter: Optional[Filter] = Filter(json_decoder.decode(filter_json))
+            event_filter: Optional[Filter] = Filter(
+                self._hs, json_decoder.decode(filter_json)
+            )
         else:
             event_filter = None
 
@@ -914,7 +920,7 @@ class RoomTypingRestServlet(RestServlet):
         # If we're not on the typing writer instance we should scream if we get
         # requests.
         self._is_typing_writer = (
-            hs.config.worker.writers.typing == hs.get_instance_name()
+            hs.get_instance_name() in hs.config.worker.writers.typing
         )
 
     async def on_PUT(
diff --git a/synapse/rest/client/room_batch.py b/synapse/rest/client/room_batch.py
index 982763f2d8..c9509d2ae3 100644
--- a/synapse/rest/client/room_batch.py
+++ b/synapse/rest/client/room_batch.py
@@ -139,20 +139,22 @@ class RoomBatchSendEventRestServlet(RestServlet):
                 errcode=Codes.INVALID_PARAM,
             )
 
+        state_event_ids_at_start = []
         # Create and persist all of the state events that float off on their own
         # before the batch. These will most likely be all of the invite/member
         # state events used to auth the upcoming historical messages.
-        state_event_ids_at_start = (
-            await self.room_batch_handler.persist_state_events_at_start(
-                state_events_at_start=body["state_events_at_start"],
-                room_id=room_id,
-                initial_auth_event_ids=auth_event_ids,
-                app_service_requester=requester,
+        if body["state_events_at_start"]:
+            state_event_ids_at_start = (
+                await self.room_batch_handler.persist_state_events_at_start(
+                    state_events_at_start=body["state_events_at_start"],
+                    room_id=room_id,
+                    initial_auth_event_ids=auth_event_ids,
+                    app_service_requester=requester,
+                )
             )
-        )
-        # Update our ongoing auth event ID list with all of the new state we
-        # just created
-        auth_event_ids.extend(state_event_ids_at_start)
+            # Update our ongoing auth event ID list with all of the new state we
+            # just created
+            auth_event_ids.extend(state_event_ids_at_start)
 
         inherited_depth = await self.room_batch_handler.inherit_depth_from_prev_ids(
             prev_event_ids_from_query
@@ -205,8 +207,11 @@ class RoomBatchSendEventRestServlet(RestServlet):
 
         # Also connect the historical event chain to the end of the floating
         # state chain, which causes the HS to ask for the state at the start of
-        # the batch later.
-        prev_event_ids = [state_event_ids_at_start[-1]]
+        # the batch later. If there is no state chain to connect to, just make
+        # the insertion event float itself.
+        prev_event_ids = []
+        if len(state_event_ids_at_start):
+            prev_event_ids = [state_event_ids_at_start[-1]]
 
         # Create and persist all of the historical events as well as insertion
         # and batch meta events to make the batch navigable in the DAG.
diff --git a/synapse/rest/client/sync.py b/synapse/rest/client/sync.py
index 913216a7c4..8c0fdb1940 100644
--- a/synapse/rest/client/sync.py
+++ b/synapse/rest/client/sync.py
@@ -29,7 +29,7 @@ from typing import (
 
 from synapse.api.constants import Membership, PresenceState
 from synapse.api.errors import Codes, StoreError, SynapseError
-from synapse.api.filtering import DEFAULT_FILTER_COLLECTION, FilterCollection
+from synapse.api.filtering import FilterCollection
 from synapse.api.presence import UserPresenceState
 from synapse.events import EventBase
 from synapse.events.utils import (
@@ -150,7 +150,7 @@ class SyncRestServlet(RestServlet):
         request_key = (user, timeout, since, filter_id, full_state, device_id)
 
         if filter_id is None:
-            filter_collection = DEFAULT_FILTER_COLLECTION
+            filter_collection = self.filtering.DEFAULT_FILTER_COLLECTION
         elif filter_id.startswith("{"):
             try:
                 filter_object = json_decoder.decode(filter_id)
@@ -160,7 +160,7 @@ class SyncRestServlet(RestServlet):
             except Exception:
                 raise SynapseError(400, "Invalid filter JSON")
             self.filtering.check_valid_filter(filter_object)
-            filter_collection = FilterCollection(filter_object)
+            filter_collection = FilterCollection(self.hs, filter_object)
         else:
             try:
                 filter_collection = await self.filtering.get_user_filter(
diff --git a/synapse/rest/well_known.py b/synapse/rest/well_known.py
index edbf5ce5d0..04b035a1b1 100644
--- a/synapse/rest/well_known.py
+++ b/synapse/rest/well_known.py
@@ -34,8 +34,7 @@ class WellKnownBuilder:
         self._config = hs.config
 
     def get_well_known(self) -> Optional[JsonDict]:
-        # if we don't have a public_baseurl, we can't help much here.
-        if self._config.server.public_baseurl is None:
+        if not self._config.server.serve_client_wellknown:
             return None
 
         result = {"m.homeserver": {"base_url": self._config.server.public_baseurl}}
diff --git a/synapse/server.py b/synapse/server.py
index 0fbf36ba99..013a7bacaa 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -463,7 +463,7 @@ class HomeServer(metaclass=abc.ABCMeta):
 
     @cache_in_self
     def get_typing_writer_handler(self) -> TypingWriterHandler:
-        if self.config.worker.writers.typing == self.get_instance_name():
+        if self.get_instance_name() in self.config.worker.writers.typing:
             return TypingWriterHandler(self)
         else:
             raise Exception("Workers cannot write typing")
@@ -474,7 +474,7 @@ class HomeServer(metaclass=abc.ABCMeta):
 
     @cache_in_self
     def get_typing_handler(self) -> FollowerTypingHandler:
-        if self.config.worker.writers.typing == self.get_instance_name():
+        if self.get_instance_name() in self.config.worker.writers.typing:
             # Use get_typing_writer_handler to ensure that we use the same
             # cached version.
             return self.get_typing_writer_handler()
diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index 82b31d24f1..b9a8ca997e 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -100,29 +100,58 @@ class BackgroundUpdater:
         ] = {}
         self._all_done = False
 
+        # Whether we're currently running updates
+        self._running = False
+
+        # Whether background updates are enabled. This allows us to
+        # enable/disable background updates via the admin API.
+        self.enabled = True
+
+    def get_current_update(self) -> Optional[BackgroundUpdatePerformance]:
+        """Returns the current background update, if any."""
+
+        update_name = self._current_background_update
+        if not update_name:
+            return None
+
+        perf = self._background_update_performance.get(update_name)
+        if not perf:
+            perf = BackgroundUpdatePerformance(update_name)
+
+        return perf
+
     def start_doing_background_updates(self) -> None:
-        run_as_background_process("background_updates", self.run_background_updates)
+        if self.enabled:
+            run_as_background_process("background_updates", self.run_background_updates)
 
     async def run_background_updates(self, sleep: bool = True) -> None:
-        logger.info("Starting background schema updates")
-        while True:
-            if sleep:
-                await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000.0)
+        if self._running or not self.enabled:
+            return
 
-            try:
-                result = await self.do_next_background_update(
-                    self.BACKGROUND_UPDATE_DURATION_MS
-                )
-            except Exception:
-                logger.exception("Error doing update")
-            else:
-                if result:
-                    logger.info(
-                        "No more background updates to do."
-                        " Unscheduling background update task."
+        self._running = True
+
+        try:
+            logger.info("Starting background schema updates")
+            while self.enabled:
+                if sleep:
+                    await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000.0)
+
+                try:
+                    result = await self.do_next_background_update(
+                        self.BACKGROUND_UPDATE_DURATION_MS
                     )
-                    self._all_done = True
-                    return None
+                except Exception:
+                    logger.exception("Error doing update")
+                else:
+                    if result:
+                        logger.info(
+                            "No more background updates to do."
+                            " Unscheduling background update task."
+                        )
+                        self._all_done = True
+                        return None
+        finally:
+            self._running = False
 
     async def has_completed_background_updates(self) -> bool:
         """Check if all the background updates have completed
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 5c71e27518..d4cab69ebf 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -446,6 +446,10 @@ class DatabasePool:
                 self._check_safe_to_upsert,
             )
 
+    def name(self) -> str:
+        "Return the name of this database"
+        return self._database_config.name
+
     def is_running(self) -> bool:
         """Is the database pool currently running"""
         return self._db_pool.running
diff --git a/synapse/storage/databases/main/appservice.py b/synapse/storage/databases/main/appservice.py
index 2da2659f41..baec35ee27 100644
--- a/synapse/storage/databases/main/appservice.py
+++ b/synapse/storage/databases/main/appservice.py
@@ -412,16 +412,16 @@ class ApplicationServiceTransactionWorkerStore(
         )
 
     async def set_type_stream_id_for_appservice(
-        self, service: ApplicationService, type: str, pos: Optional[int]
+        self, service: ApplicationService, stream_type: str, pos: Optional[int]
     ) -> None:
-        if type not in ("read_receipt", "presence"):
+        if stream_type not in ("read_receipt", "presence"):
             raise ValueError(
                 "Expected type to be a valid application stream id type, got %s"
-                % (type,)
+                % (stream_type,)
             )
 
         def set_type_stream_id_for_appservice_txn(txn):
-            stream_id_type = "%s_stream_id" % type
+            stream_id_type = "%s_stream_id" % stream_type
             txn.execute(
                 "UPDATE application_services_state SET %s = ? WHERE as_id=?"
                 % stream_id_type,
diff --git a/synapse/storage/databases/main/deviceinbox.py b/synapse/storage/databases/main/deviceinbox.py
index 264e625bd7..ae3afdd5d2 100644
--- a/synapse/storage/databases/main/deviceinbox.py
+++ b/synapse/storage/databases/main/deviceinbox.py
@@ -134,7 +134,10 @@ class DeviceInboxWorkerStore(SQLBaseStore):
             limit: The maximum number of messages to retrieve.
 
         Returns:
-            A list of messages for the device and where in the stream the messages got to.
+            A tuple containing:
+                * A list of messages for the device.
+                * The max stream token of these messages. There may be more to retrieve
+                  if the given limit was reached.
         """
         has_changed = self._device_inbox_stream_cache.has_entity_changed(
             user_id, last_stream_id
@@ -153,12 +156,19 @@ class DeviceInboxWorkerStore(SQLBaseStore):
             txn.execute(
                 sql, (user_id, device_id, last_stream_id, current_stream_id, limit)
             )
+
             messages = []
+            stream_pos = current_stream_id
+
             for row in txn:
                 stream_pos = row[0]
                 messages.append(db_to_json(row[1]))
+
+            # If the limit was not reached we know that there's no more data for this
+            # user/device pair up to current_stream_id.
             if len(messages) < limit:
                 stream_pos = current_stream_id
+
             return messages, stream_pos
 
         return await self.db_pool.runInteraction(
@@ -260,13 +270,20 @@ class DeviceInboxWorkerStore(SQLBaseStore):
                 " LIMIT ?"
             )
             txn.execute(sql, (destination, last_stream_id, current_stream_id, limit))
+
             messages = []
+            stream_pos = current_stream_id
+
             for row in txn:
                 stream_pos = row[0]
                 messages.append(db_to_json(row[1]))
+
+            # If the limit was not reached we know that there's no more data for this
+            # user/device pair up to current_stream_id.
             if len(messages) < limit:
                 log_kv({"message": "Set stream position to current position"})
                 stream_pos = current_stream_id
+
             return messages, stream_pos
 
         return await self.db_pool.runInteraction(
@@ -372,8 +389,8 @@ class DeviceInboxWorkerStore(SQLBaseStore):
         """Used to send messages from this server.
 
         Args:
-            local_messages_by_user_and_device:
-                Dictionary of user_id to device_id to message.
+            local_messages_by_user_then_device:
+                Dictionary of recipient user_id to recipient device_id to message.
             remote_messages_by_destination:
                 Dictionary of destination server_name to the EDU JSON to send.
 
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index ae37901be9..c6bf316d5b 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -28,6 +28,7 @@ from typing import (
 
 import attr
 from constantly import NamedConstant, Names
+from prometheus_client import Gauge
 from typing_extensions import Literal
 
 from twisted.internet import defer
@@ -81,6 +82,12 @@ EVENT_QUEUE_ITERATIONS = 3  # No. times we block waiting for requests for events
 EVENT_QUEUE_TIMEOUT_S = 0.1  # Timeout when waiting for requests for events
 
 
+event_fetch_ongoing_gauge = Gauge(
+    "synapse_event_fetch_ongoing",
+    "The number of event fetchers that are running",
+)
+
+
 @attr.s(slots=True, auto_attribs=True)
 class _EventCacheEntry:
     event: EventBase
@@ -222,6 +229,7 @@ class EventsWorkerStore(SQLBaseStore):
         self._event_fetch_lock = threading.Condition()
         self._event_fetch_list = []
         self._event_fetch_ongoing = 0
+        event_fetch_ongoing_gauge.set(self._event_fetch_ongoing)
 
         # We define this sequence here so that it can be referenced from both
         # the DataStore and PersistEventStore.
@@ -732,28 +740,31 @@ class EventsWorkerStore(SQLBaseStore):
         """Takes a database connection and waits for requests for events from
         the _event_fetch_list queue.
         """
-        i = 0
-        while True:
-            with self._event_fetch_lock:
-                event_list = self._event_fetch_list
-                self._event_fetch_list = []
-
-                if not event_list:
-                    single_threaded = self.database_engine.single_threaded
-                    if (
-                        not self.USE_DEDICATED_DB_THREADS_FOR_EVENT_FETCHING
-                        or single_threaded
-                        or i > EVENT_QUEUE_ITERATIONS
-                    ):
-                        self._event_fetch_ongoing -= 1
-                        return
-                    else:
-                        self._event_fetch_lock.wait(EVENT_QUEUE_TIMEOUT_S)
-                        i += 1
-                        continue
-                i = 0
-
-            self._fetch_event_list(conn, event_list)
+        try:
+            i = 0
+            while True:
+                with self._event_fetch_lock:
+                    event_list = self._event_fetch_list
+                    self._event_fetch_list = []
+
+                    if not event_list:
+                        single_threaded = self.database_engine.single_threaded
+                        if (
+                            not self.USE_DEDICATED_DB_THREADS_FOR_EVENT_FETCHING
+                            or single_threaded
+                            or i > EVENT_QUEUE_ITERATIONS
+                        ):
+                            break
+                        else:
+                            self._event_fetch_lock.wait(EVENT_QUEUE_TIMEOUT_S)
+                            i += 1
+                            continue
+                    i = 0
+
+                self._fetch_event_list(conn, event_list)
+        finally:
+            self._event_fetch_ongoing -= 1
+            event_fetch_ongoing_gauge.set(self._event_fetch_ongoing)
 
     def _fetch_event_list(
         self, conn: Connection, event_list: List[Tuple[List[str], defer.Deferred]]
@@ -977,6 +988,7 @@ class EventsWorkerStore(SQLBaseStore):
 
             if self._event_fetch_ongoing < EVENT_QUEUE_THREADS:
                 self._event_fetch_ongoing += 1
+                event_fetch_ongoing_gauge.set(self._event_fetch_ongoing)
                 should_start = True
             else:
                 should_start = False
diff --git a/synapse/storage/databases/main/lock.py b/synapse/storage/databases/main/lock.py
index 3d1dff660b..3d0df0cbd4 100644
--- a/synapse/storage/databases/main/lock.py
+++ b/synapse/storage/databases/main/lock.py
@@ -14,6 +14,7 @@
 import logging
 from types import TracebackType
 from typing import TYPE_CHECKING, Dict, Optional, Tuple, Type
+from weakref import WeakValueDictionary
 
 from twisted.internet.interfaces import IReactorCore
 
@@ -61,7 +62,7 @@ class LockStore(SQLBaseStore):
 
         # A map from `(lock_name, lock_key)` to the token of any locks that we
         # think we currently hold.
-        self._live_tokens: Dict[Tuple[str, str], str] = {}
+        self._live_tokens: Dict[Tuple[str, str], Lock] = WeakValueDictionary()
 
         # When we shut down we want to remove the locks. Technically this can
         # lead to a race, as we may drop the lock while we are still processing.
@@ -80,10 +81,10 @@ class LockStore(SQLBaseStore):
 
         # We need to take a copy of the tokens dict as dropping the locks will
         # cause the dictionary to change.
-        tokens = dict(self._live_tokens)
+        locks = dict(self._live_tokens)
 
-        for (lock_name, lock_key), token in tokens.items():
-            await self._drop_lock(lock_name, lock_key, token)
+        for lock in locks.values():
+            await lock.release()
 
         logger.info("Dropped locks due to shutdown")
 
@@ -93,6 +94,11 @@ class LockStore(SQLBaseStore):
         used (otherwise the lock will leak).
         """
 
+        # Check if this process has taken out a lock and if it's still valid.
+        lock = self._live_tokens.get((lock_name, lock_key))
+        if lock and await lock.is_still_valid():
+            return None
+
         now = self._clock.time_msec()
         token = random_string(6)
 
@@ -100,7 +106,9 @@ class LockStore(SQLBaseStore):
 
             def _try_acquire_lock_txn(txn: LoggingTransaction) -> bool:
                 # We take out the lock if either a) there is no row for the lock
-                # already or b) the existing row has timed out.
+                # already, b) the existing row has timed out, or c) the row is
+                # for this instance (which means the process got killed and
+                # restarted)
                 sql = """
                     INSERT INTO worker_locks (lock_name, lock_key, instance_name, token, last_renewed_ts)
                     VALUES (?, ?, ?, ?, ?)
@@ -112,6 +120,7 @@ class LockStore(SQLBaseStore):
                             last_renewed_ts = EXCLUDED.last_renewed_ts
                         WHERE
                             worker_locks.last_renewed_ts < ?
+                            OR worker_locks.instance_name = EXCLUDED.instance_name
                 """
                 txn.execute(
                     sql,
@@ -148,11 +157,11 @@ class LockStore(SQLBaseStore):
                     WHERE
                         lock_name = ?
                         AND lock_key = ?
-                        AND last_renewed_ts < ?
+                        AND (last_renewed_ts < ? OR instance_name = ?)
                 """
                 txn.execute(
                     sql,
-                    (lock_name, lock_key, now - _LOCK_TIMEOUT_MS),
+                    (lock_name, lock_key, now - _LOCK_TIMEOUT_MS, self._instance_name),
                 )
 
                 inserted = self.db_pool.simple_upsert_txn_emulated(
@@ -179,9 +188,7 @@ class LockStore(SQLBaseStore):
             if not did_lock:
                 return None
 
-        self._live_tokens[(lock_name, lock_key)] = token
-
-        return Lock(
+        lock = Lock(
             self._reactor,
             self._clock,
             self,
@@ -190,6 +197,10 @@ class LockStore(SQLBaseStore):
             token=token,
         )
 
+        self._live_tokens[(lock_name, lock_key)] = lock
+
+        return lock
+
     async def _is_lock_still_valid(
         self, lock_name: str, lock_key: str, token: str
     ) -> bool:
diff --git a/synapse/storage/databases/main/relations.py b/synapse/storage/databases/main/relations.py
index 53576ad52f..907af10995 100644
--- a/synapse/storage/databases/main/relations.py
+++ b/synapse/storage/databases/main/relations.py
@@ -20,7 +20,7 @@ import attr
 from synapse.api.constants import RelationTypes
 from synapse.events import EventBase
 from synapse.storage._base import SQLBaseStore
-from synapse.storage.database import LoggingTransaction
+from synapse.storage.database import LoggingTransaction, make_in_list_sql_clause
 from synapse.storage.databases.main.stream import generate_pagination_where_clause
 from synapse.storage.relations import (
     AggregationPaginationToken,
@@ -334,6 +334,62 @@ class RelationsWorkerStore(SQLBaseStore):
 
         return count, latest_event
 
+    async def events_have_relations(
+        self,
+        parent_ids: List[str],
+        relation_senders: Optional[List[str]],
+        relation_types: Optional[List[str]],
+    ) -> List[str]:
+        """Check which events have a relationship from the given senders of the
+        given types.
+
+        Args:
+            parent_ids: The events being annotated
+            relation_senders: The relation senders to check.
+            relation_types: The relation types to check.
+
+        Returns:
+            True if the event has at least one relationship from one of the given senders of the given type.
+        """
+        # If no restrictions are given then the event has the required relations.
+        if not relation_senders and not relation_types:
+            return parent_ids
+
+        sql = """
+            SELECT relates_to_id FROM event_relations
+            INNER JOIN events USING (event_id)
+            WHERE
+                %s;
+        """
+
+        def _get_if_event_has_relations(txn) -> List[str]:
+            clauses: List[str] = []
+            clause, args = make_in_list_sql_clause(
+                txn.database_engine, "relates_to_id", parent_ids
+            )
+            clauses.append(clause)
+
+            if relation_senders:
+                clause, temp_args = make_in_list_sql_clause(
+                    txn.database_engine, "sender", relation_senders
+                )
+                clauses.append(clause)
+                args.extend(temp_args)
+            if relation_types:
+                clause, temp_args = make_in_list_sql_clause(
+                    txn.database_engine, "relation_type", relation_types
+                )
+                clauses.append(clause)
+                args.extend(temp_args)
+
+            txn.execute(sql % " AND ".join(clauses), args)
+
+            return [row[0] for row in txn]
+
+        return await self.db_pool.runInteraction(
+            "get_if_event_has_relations", _get_if_event_has_relations
+        )
+
     async def has_user_annotated_event(
         self, parent_id: str, event_type: str, aggregation_key: str, sender: str
     ) -> bool:
diff --git a/synapse/storage/databases/main/room.py b/synapse/storage/databases/main/room.py
index cefc77fa0f..17b398bb69 100644
--- a/synapse/storage/databases/main/room.py
+++ b/synapse/storage/databases/main/room.py
@@ -1751,7 +1751,12 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
         )
 
     async def block_room(self, room_id: str, user_id: str) -> None:
-        """Marks the room as blocked. Can be called multiple times.
+        """Marks the room as blocked.
+
+        Can be called multiple times (though we'll only track the last user to
+        block this room).
+
+        Can be called on a room unknown to this homeserver.
 
         Args:
             room_id: Room to block
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index dc7884b1c0..42dc807d17 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -272,31 +272,37 @@ def filter_to_clause(event_filter: Optional[Filter]) -> Tuple[str, List[str]]:
     args = []
 
     if event_filter.types:
-        clauses.append("(%s)" % " OR ".join("type = ?" for _ in event_filter.types))
+        clauses.append(
+            "(%s)" % " OR ".join("event.type = ?" for _ in event_filter.types)
+        )
         args.extend(event_filter.types)
 
     for typ in event_filter.not_types:
-        clauses.append("type != ?")
+        clauses.append("event.type != ?")
         args.append(typ)
 
     if event_filter.senders:
-        clauses.append("(%s)" % " OR ".join("sender = ?" for _ in event_filter.senders))
+        clauses.append(
+            "(%s)" % " OR ".join("event.sender = ?" for _ in event_filter.senders)
+        )
         args.extend(event_filter.senders)
 
     for sender in event_filter.not_senders:
-        clauses.append("sender != ?")
+        clauses.append("event.sender != ?")
         args.append(sender)
 
     if event_filter.rooms:
-        clauses.append("(%s)" % " OR ".join("room_id = ?" for _ in event_filter.rooms))
+        clauses.append(
+            "(%s)" % " OR ".join("event.room_id = ?" for _ in event_filter.rooms)
+        )
         args.extend(event_filter.rooms)
 
     for room_id in event_filter.not_rooms:
-        clauses.append("room_id != ?")
+        clauses.append("event.room_id != ?")
         args.append(room_id)
 
     if event_filter.contains_url:
-        clauses.append("contains_url = ?")
+        clauses.append("event.contains_url = ?")
         args.append(event_filter.contains_url)
 
     # We're only applying the "labels" filter on the database query, because applying the
@@ -307,6 +313,23 @@ def filter_to_clause(event_filter: Optional[Filter]) -> Tuple[str, List[str]]:
         clauses.append("(%s)" % " OR ".join("label = ?" for _ in event_filter.labels))
         args.extend(event_filter.labels)
 
+    # Filter on relation_senders / relation types from the joined tables.
+    if event_filter.relation_senders:
+        clauses.append(
+            "(%s)"
+            % " OR ".join(
+                "related_event.sender = ?" for _ in event_filter.relation_senders
+            )
+        )
+        args.extend(event_filter.relation_senders)
+
+    if event_filter.relation_types:
+        clauses.append(
+            "(%s)"
+            % " OR ".join("relation_type = ?" for _ in event_filter.relation_types)
+        )
+        args.extend(event_filter.relation_types)
+
     return " AND ".join(clauses), args
 
 
@@ -1116,7 +1139,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore, metaclass=abc.ABCMeta):
 
         bounds = generate_pagination_where_clause(
             direction=direction,
-            column_names=("topological_ordering", "stream_ordering"),
+            column_names=("event.topological_ordering", "event.stream_ordering"),
             from_token=from_bound,
             to_token=to_bound,
             engine=self.database_engine,
@@ -1133,32 +1156,51 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore, metaclass=abc.ABCMeta):
 
         select_keywords = "SELECT"
         join_clause = ""
+        # Using DISTINCT in this SELECT query is quite expensive, because it
+        # requires the engine to sort on the entire (not limited) result set,
+        # i.e. the entire events table. Only use it in scenarios that could result
+        # in the same event ID occurring multiple times in the results.
+        needs_distinct = False
         if event_filter and event_filter.labels:
             # If we're not filtering on a label, then joining on event_labels will
             # return as many row for a single event as the number of labels it has. To
             # avoid this, only join if we're filtering on at least one label.
-            join_clause = """
+            join_clause += """
                 LEFT JOIN event_labels
                 USING (event_id, room_id, topological_ordering)
             """
             if len(event_filter.labels) > 1:
-                # Using DISTINCT in this SELECT query is quite expensive, because it
-                # requires the engine to sort on the entire (not limited) result set,
-                # i.e. the entire events table. We only need to use it when we're
-                # filtering on more than two labels, because that's the only scenario
-                # in which we can possibly to get multiple times the same event ID in
-                # the results.
-                select_keywords += "DISTINCT"
+                # Multiple labels could cause the same event to appear multiple times.
+                needs_distinct = True
+
+        # If there is a filter on relation_senders and relation_types join to the
+        # relations table.
+        if event_filter and (
+            event_filter.relation_senders or event_filter.relation_types
+        ):
+            # Filtering by relations could cause the same event to appear multiple
+            # times (since there's no limit on the number of relations to an event).
+            needs_distinct = True
+            join_clause += """
+                LEFT JOIN event_relations AS relation ON (event.event_id = relation.relates_to_id)
+            """
+            if event_filter.relation_senders:
+                join_clause += """
+                    LEFT JOIN events AS related_event ON (relation.event_id = related_event.event_id)
+                """
+
+        if needs_distinct:
+            select_keywords += " DISTINCT"
 
         sql = """
             %(select_keywords)s
-                event_id, instance_name,
-                topological_ordering, stream_ordering
-            FROM events
+                event.event_id, event.instance_name,
+                event.topological_ordering, event.stream_ordering
+            FROM events AS event
             %(join_clause)s
-            WHERE outlier = ? AND room_id = ? AND %(bounds)s
-            ORDER BY topological_ordering %(order)s,
-            stream_ordering %(order)s LIMIT ?
+            WHERE event.outlier = ? AND event.room_id = ? AND %(bounds)s
+            ORDER BY event.topological_ordering %(order)s,
+            event.stream_ordering %(order)s LIMIT ?
         """ % {
             "select_keywords": select_keywords,
             "join_clause": join_clause,
diff --git a/synapse/storage/prepare_database.py b/synapse/storage/prepare_database.py
index 1629d2a53c..8b9c6adae2 100644
--- a/synapse/storage/prepare_database.py
+++ b/synapse/storage/prepare_database.py
@@ -133,22 +133,23 @@ def prepare_database(
 
             # if it's a worker app, refuse to upgrade the database, to avoid multiple
             # workers doing it at once.
-            if (
-                config.worker.worker_app is not None
-                and version_info.current_version != SCHEMA_VERSION
-            ):
+            if config.worker.worker_app is None:
+                _upgrade_existing_database(
+                    cur,
+                    version_info,
+                    database_engine,
+                    config,
+                    databases=databases,
+                )
+            elif version_info.current_version < SCHEMA_VERSION:
+                # If the DB is on an older version than we expect then we refuse
+                # to start the worker (as the main process needs to run first to
+                # update the schema).
                 raise UpgradeDatabaseException(
                     OUTDATED_SCHEMA_ON_WORKER_ERROR
                     % (SCHEMA_VERSION, version_info.current_version)
                 )
 
-            _upgrade_existing_database(
-                cur,
-                version_info,
-                database_engine,
-                config,
-                databases=databases,
-            )
         else:
             logger.info("%r: Initialising new database", databases)