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-rw-r--r--synapse/__init__.py2
-rw-r--r--synapse/api/constants.py12
-rw-r--r--synapse/api/errors.py16
-rw-r--r--synapse/api/room_versions.py17
-rw-r--r--synapse/app/client_reader.py2
-rw-r--r--synapse/config/homeserver.py42
-rw-r--r--synapse/config/server.py38
-rw-r--r--synapse/config/stats.py60
-rw-r--r--synapse/crypto/keyring.py567
-rw-r--r--synapse/events/__init__.py31
-rw-r--r--synapse/events/builder.py13
-rw-r--r--synapse/events/utils.py59
-rw-r--r--synapse/federation/federation_server.py14
-rw-r--r--synapse/handlers/events.py3
-rw-r--r--synapse/handlers/federation.py308
-rw-r--r--synapse/handlers/message.py19
-rw-r--r--synapse/handlers/register.py11
-rw-r--r--synapse/handlers/room.py9
-rw-r--r--synapse/handlers/room_member.py2
-rw-r--r--synapse/handlers/stats.py325
-rw-r--r--synapse/http/servlet.py2
-rw-r--r--synapse/python_dependencies.py50
-rw-r--r--synapse/replication/slave/storage/events.py14
-rw-r--r--synapse/replication/tcp/streams/_base.py1
-rw-r--r--synapse/replication/tcp/streams/events.py11
-rw-r--r--synapse/rest/__init__.py2
-rw-r--r--synapse/rest/client/v2_alpha/capabilities.py5
-rw-r--r--synapse/rest/client/v2_alpha/register.py22
-rw-r--r--synapse/rest/client/v2_alpha/relations.py338
-rw-r--r--synapse/rest/client/v2_alpha/sync.py3
-rw-r--r--synapse/rest/key/v2/remote_key_resource.py6
-rw-r--r--synapse/rest/media/v1/media_repository.py9
-rw-r--r--synapse/rest/media/v1/thumbnailer.py35
-rw-r--r--synapse/server.py6
-rw-r--r--synapse/storage/__init__.py4
-rw-r--r--synapse/storage/events.py26
-rw-r--r--synapse/storage/events_worker.py26
-rw-r--r--synapse/storage/keys.py90
-rw-r--r--synapse/storage/relations.py476
-rw-r--r--synapse/storage/roommember.py32
-rw-r--r--synapse/storage/schema/delta/54/add_validity_to_server_keys.sql23
-rw-r--r--synapse/storage/schema/delta/54/relations.sql27
-rw-r--r--synapse/storage/schema/delta/54/stats.sql80
-rw-r--r--synapse/storage/state_deltas.py12
-rw-r--r--synapse/storage/stats.py450
-rw-r--r--synapse/storage/stream.py194
46 files changed, 2922 insertions, 572 deletions
diff --git a/synapse/__init__.py b/synapse/__init__.py
index bf9e810da6..4f95778eea 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -27,4 +27,4 @@ try:
 except ImportError:
     pass
 
-__version__ = "0.99.4"
+__version__ = "0.99.5.1"
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 8547a63535..ee129c8689 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -23,6 +23,9 @@ MAX_DEPTH = 2**63 - 1
 # the maximum length for a room alias is 255 characters
 MAX_ALIAS_LENGTH = 255
 
+# the maximum length for a user id is 255 characters
+MAX_USERID_LENGTH = 255
+
 
 class Membership(object):
 
@@ -76,6 +79,7 @@ class EventTypes(object):
 
     RoomHistoryVisibility = "m.room.history_visibility"
     CanonicalAlias = "m.room.canonical_alias"
+    Encryption = "m.room.encryption"
     RoomAvatar = "m.room.avatar"
     RoomEncryption = "m.room.encryption"
     GuestAccess = "m.room.guest_access"
@@ -116,3 +120,11 @@ class UserTypes(object):
     """
     SUPPORT = "support"
     ALL_USER_TYPES = (SUPPORT,)
+
+
+class RelationTypes(object):
+    """The types of relations known to this server.
+    """
+    ANNOTATION = "m.annotation"
+    REPLACE = "m.replace"
+    REFERENCE = "m.reference"
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index ff89259dec..e91697049c 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -328,9 +328,23 @@ class RoomKeysVersionError(SynapseError):
         self.current_version = current_version
 
 
+class UnsupportedRoomVersionError(SynapseError):
+    """The client's request to create a room used a room version that the server does
+    not support."""
+    def __init__(self):
+        super(UnsupportedRoomVersionError, self).__init__(
+            code=400,
+            msg="Homeserver does not support this room version",
+            errcode=Codes.UNSUPPORTED_ROOM_VERSION,
+        )
+
+
 class IncompatibleRoomVersionError(SynapseError):
-    """A server is trying to join a room whose version it does not support."""
+    """A server is trying to join a room whose version it does not support.
 
+    Unlike UnsupportedRoomVersionError, it is specific to the case of the make_join
+    failing.
+    """
     def __init__(self, room_version):
         super(IncompatibleRoomVersionError, self).__init__(
             code=400,
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index e77abe1040..4085bd10b9 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -19,13 +19,15 @@ class EventFormatVersions(object):
     """This is an internal enum for tracking the version of the event format,
     independently from the room version.
     """
-    V1 = 1   # $id:server format
-    V2 = 2   # MSC1659-style $hash format: introduced for room v3
+    V1 = 1   # $id:server event id format
+    V2 = 2   # MSC1659-style $hash event id format: introduced for room v3
+    V3 = 3   # MSC1884-style $hash format: introduced for room v4
 
 
 KNOWN_EVENT_FORMAT_VERSIONS = {
     EventFormatVersions.V1,
     EventFormatVersions.V2,
+    EventFormatVersions.V3,
 }
 
 
@@ -75,10 +77,12 @@ class RoomVersions(object):
         EventFormatVersions.V2,
         StateResolutionVersions.V2,
     )
-
-
-# the version we will give rooms which are created on this server
-DEFAULT_ROOM_VERSION = RoomVersions.V1
+    V4 = RoomVersion(
+        "4",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+    )
 
 
 KNOWN_ROOM_VERSIONS = {
@@ -87,5 +91,6 @@ KNOWN_ROOM_VERSIONS = {
         RoomVersions.V2,
         RoomVersions.V3,
         RoomVersions.STATE_V2_TEST,
+        RoomVersions.V4,
     )
 }   # type: dict[str, RoomVersion]
diff --git a/synapse/app/client_reader.py b/synapse/app/client_reader.py
index 864f1eac48..a16e037f32 100644
--- a/synapse/app/client_reader.py
+++ b/synapse/app/client_reader.py
@@ -38,6 +38,7 @@ from synapse.replication.slave.storage.devices import SlavedDeviceStore
 from synapse.replication.slave.storage.directory import DirectoryStore
 from synapse.replication.slave.storage.events import SlavedEventStore
 from synapse.replication.slave.storage.keys import SlavedKeyStore
+from synapse.replication.slave.storage.profile import SlavedProfileStore
 from synapse.replication.slave.storage.push_rule import SlavedPushRuleStore
 from synapse.replication.slave.storage.receipts import SlavedReceiptsStore
 from synapse.replication.slave.storage.registration import SlavedRegistrationStore
@@ -81,6 +82,7 @@ class ClientReaderSlavedStore(
     SlavedApplicationServiceStore,
     SlavedRegistrationStore,
     SlavedTransactionStore,
+    SlavedProfileStore,
     SlavedClientIpStore,
     BaseSlavedStore,
 ):
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index 727fdc54d8..5c4fc8ff21 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -13,6 +13,7 @@
 # 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.
+
 from .api import ApiConfig
 from .appservice import AppServiceConfig
 from .captcha import CaptchaConfig
@@ -36,20 +37,41 @@ from .saml2_config import SAML2Config
 from .server import ServerConfig
 from .server_notices_config import ServerNoticesConfig
 from .spam_checker import SpamCheckerConfig
+from .stats import StatsConfig
 from .tls import TlsConfig
 from .user_directory import UserDirectoryConfig
 from .voip import VoipConfig
 from .workers import WorkerConfig
 
 
-class HomeServerConfig(ServerConfig, TlsConfig, DatabaseConfig, LoggingConfig,
-                       RatelimitConfig, ContentRepositoryConfig, CaptchaConfig,
-                       VoipConfig, RegistrationConfig, MetricsConfig, ApiConfig,
-                       AppServiceConfig, KeyConfig, SAML2Config, CasConfig,
-                       JWTConfig, PasswordConfig, EmailConfig,
-                       WorkerConfig, PasswordAuthProviderConfig, PushConfig,
-                       SpamCheckerConfig, GroupsConfig, UserDirectoryConfig,
-                       ConsentConfig,
-                       ServerNoticesConfig, RoomDirectoryConfig,
-                       ):
+class HomeServerConfig(
+    ServerConfig,
+    TlsConfig,
+    DatabaseConfig,
+    LoggingConfig,
+    RatelimitConfig,
+    ContentRepositoryConfig,
+    CaptchaConfig,
+    VoipConfig,
+    RegistrationConfig,
+    MetricsConfig,
+    ApiConfig,
+    AppServiceConfig,
+    KeyConfig,
+    SAML2Config,
+    CasConfig,
+    JWTConfig,
+    PasswordConfig,
+    EmailConfig,
+    WorkerConfig,
+    PasswordAuthProviderConfig,
+    PushConfig,
+    SpamCheckerConfig,
+    GroupsConfig,
+    UserDirectoryConfig,
+    ConsentConfig,
+    StatsConfig,
+    ServerNoticesConfig,
+    RoomDirectoryConfig,
+):
     pass
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 1b8968608e..e763e19e15 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -20,6 +20,7 @@ import os.path
 
 from netaddr import IPSet
 
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.http.endpoint import parse_and_validate_server_name
 from synapse.python_dependencies import DependencyException, check_requirements
 
@@ -35,6 +36,8 @@ logger = logging.Logger(__name__)
 # in the list.
 DEFAULT_BIND_ADDRESSES = ['::', '0.0.0.0']
 
+DEFAULT_ROOM_VERSION = "1"
+
 
 class ServerConfig(Config):
 
@@ -88,6 +91,22 @@ class ServerConfig(Config):
             "restrict_public_rooms_to_local_users", False,
         )
 
+        default_room_version = config.get(
+            "default_room_version", DEFAULT_ROOM_VERSION,
+        )
+
+        # Ensure room version is a str
+        default_room_version = str(default_room_version)
+
+        if default_room_version not in KNOWN_ROOM_VERSIONS:
+            raise ConfigError(
+                "Unknown default_room_version: %s, known room versions: %s" %
+                (default_room_version, list(KNOWN_ROOM_VERSIONS.keys()))
+            )
+
+        # Get the actual room version object rather than just the identifier
+        self.default_room_version = KNOWN_ROOM_VERSIONS[default_room_version]
+
         # whether to enable search. If disabled, new entries will not be inserted
         # into the search tables and they will not be indexed. Users will receive
         # errors when attempting to search for messages.
@@ -101,6 +120,11 @@ class ServerConfig(Config):
             "block_non_admin_invites", False,
         )
 
+        # Whether to enable experimental MSC1849 (aka relations) support
+        self.experimental_msc1849_support_enabled = config.get(
+            "experimental_msc1849_support_enabled", False,
+        )
+
         # Options to control access by tracking MAU
         self.limit_usage_by_mau = config.get("limit_usage_by_mau", False)
         self.max_mau_value = 0
@@ -305,6 +329,10 @@ class ServerConfig(Config):
             unsecure_port = 8008
 
         pid_file = os.path.join(data_dir_path, "homeserver.pid")
+
+        # Bring DEFAULT_ROOM_VERSION into the local-scope for use in the
+        # default config string
+        default_room_version = DEFAULT_ROOM_VERSION
         return """\
         ## Server ##
 
@@ -379,6 +407,16 @@ class ServerConfig(Config):
         #
         #restrict_public_rooms_to_local_users: true
 
+        # The default room version for newly created rooms.
+        #
+        # Known room versions are listed here:
+        # https://matrix.org/docs/spec/#complete-list-of-room-versions
+        #
+        # For example, for room version 1, default_room_version should be set
+        # to "1".
+        #
+        #default_room_version: "%(default_room_version)s"
+
         # The GC threshold parameters to pass to `gc.set_threshold`, if defined
         #
         #gc_thresholds: [700, 10, 10]
diff --git a/synapse/config/stats.py b/synapse/config/stats.py
new file mode 100644
index 0000000000..80fc1b9dd0
--- /dev/null
+++ b/synapse/config/stats.py
@@ -0,0 +1,60 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import division
+
+import sys
+
+from ._base import Config
+
+
+class StatsConfig(Config):
+    """Stats Configuration
+    Configuration for the behaviour of synapse's stats engine
+    """
+
+    def read_config(self, config):
+        self.stats_enabled = True
+        self.stats_bucket_size = 86400
+        self.stats_retention = sys.maxsize
+        stats_config = config.get("stats", None)
+        if stats_config:
+            self.stats_enabled = stats_config.get("enabled", self.stats_enabled)
+            self.stats_bucket_size = (
+                self.parse_duration(stats_config.get("bucket_size", "1d")) / 1000
+            )
+            self.stats_retention = (
+                self.parse_duration(
+                    stats_config.get("retention", "%ds" % (sys.maxsize,))
+                )
+                / 1000
+            )
+
+    def default_config(self, config_dir_path, server_name, **kwargs):
+        return """
+        # Local statistics collection. Used in populating the room directory.
+        #
+        # 'bucket_size' controls how large each statistics timeslice is. It can
+        # be defined in a human readable short form -- e.g. "1d", "1y".
+        #
+        # 'retention' controls how long historical statistics will be kept for.
+        # It can be defined in a human readable short form -- e.g. "1d", "1y".
+        #
+        #
+        #stats:
+        #   enabled: true
+        #   bucket_size: 1d
+        #   retention: 1y
+        """
diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index d8ba870cca..d6ad7f1772 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -20,7 +20,6 @@ from collections import namedtuple
 from six import raise_from
 from six.moves import urllib
 
-import nacl.signing
 from signedjson.key import (
     decode_verify_key_bytes,
     encode_verify_key_base64,
@@ -43,6 +42,7 @@ from synapse.api.errors import (
     RequestSendFailed,
     SynapseError,
 )
+from synapse.storage.keys import FetchKeyResult
 from synapse.util import logcontext, unwrapFirstError
 from synapse.util.logcontext import (
     LoggingContext,
@@ -56,9 +56,9 @@ from synapse.util.retryutils import NotRetryingDestination
 logger = logging.getLogger(__name__)
 
 
-VerifyKeyRequest = namedtuple("VerifyRequest", (
-    "server_name", "key_ids", "json_object", "deferred"
-))
+VerifyKeyRequest = namedtuple(
+    "VerifyRequest", ("server_name", "key_ids", "json_object", "deferred")
+)
 """
 A request for a verify key to verify a JSON object.
 
@@ -80,12 +80,13 @@ class KeyLookupError(ValueError):
 
 class Keyring(object):
     def __init__(self, hs):
-        self.store = hs.get_datastore()
         self.clock = hs.get_clock()
-        self.client = hs.get_http_client()
-        self.config = hs.get_config()
-        self.perspective_servers = self.config.perspectives
-        self.hs = hs
+
+        self._key_fetchers = (
+            StoreKeyFetcher(hs),
+            PerspectivesKeyFetcher(hs),
+            ServerKeyFetcher(hs),
+        )
 
         # map from server name to Deferred. Has an entry for each server with
         # an ongoing key download; the Deferred completes once the download
@@ -96,9 +97,7 @@ class Keyring(object):
 
     def verify_json_for_server(self, server_name, json_object):
         return logcontext.make_deferred_yieldable(
-            self.verify_json_objects_for_server(
-                [(server_name, json_object)]
-            )[0]
+            self.verify_json_objects_for_server([(server_name, json_object)])[0]
         )
 
     def verify_json_objects_for_server(self, server_and_json):
@@ -130,18 +129,15 @@ class Keyring(object):
             if not key_ids:
                 return defer.fail(
                     SynapseError(
-                        400,
-                        "Not signed by %s" % (server_name,),
-                        Codes.UNAUTHORIZED,
+                        400, "Not signed by %s" % (server_name,), Codes.UNAUTHORIZED
                     )
                 )
 
-            logger.debug("Verifying for %s with key_ids %s",
-                         server_name, key_ids)
+            logger.debug("Verifying for %s with key_ids %s", server_name, key_ids)
 
             # add the key request to the queue, but don't start it off yet.
             verify_request = VerifyKeyRequest(
-                server_name, key_ids, json_object, defer.Deferred(),
+                server_name, key_ids, json_object, defer.Deferred()
             )
             verify_requests.append(verify_request)
 
@@ -179,16 +175,12 @@ class Keyring(object):
             # any other lookups until we have finished.
             # The deferreds are called with no logcontext.
             server_to_deferred = {
-                rq.server_name: defer.Deferred()
-                for rq in verify_requests
+                rq.server_name: defer.Deferred() for rq in verify_requests
             }
 
             # We want to wait for any previous lookups to complete before
             # proceeding.
-            yield self.wait_for_previous_lookups(
-                [rq.server_name for rq in verify_requests],
-                server_to_deferred,
-            )
+            yield self.wait_for_previous_lookups(server_to_deferred)
 
             # Actually start fetching keys.
             self._get_server_verify_keys(verify_requests)
@@ -216,19 +208,16 @@ class Keyring(object):
                 return res
 
             for verify_request in verify_requests:
-                verify_request.deferred.addBoth(
-                    remove_deferreds, verify_request,
-                )
+                verify_request.deferred.addBoth(remove_deferreds, verify_request)
         except Exception:
             logger.exception("Error starting key lookups")
 
     @defer.inlineCallbacks
-    def wait_for_previous_lookups(self, server_names, server_to_deferred):
+    def wait_for_previous_lookups(self, server_to_deferred):
         """Waits for any previous key lookups for the given servers to finish.
 
         Args:
-            server_names (list): list of server_names we want to lookup
-            server_to_deferred (dict): server_name to deferred which gets
+            server_to_deferred (dict[str, Deferred]): server_name to deferred which gets
                 resolved once we've finished looking up keys for that server.
                 The Deferreds should be regular twisted ones which call their
                 callbacks with no logcontext.
@@ -241,14 +230,15 @@ class Keyring(object):
         while True:
             wait_on = [
                 (server_name, self.key_downloads[server_name])
-                for server_name in server_names
+                for server_name in server_to_deferred.keys()
                 if server_name in self.key_downloads
             ]
             if not wait_on:
                 break
             logger.info(
                 "Waiting for existing lookups for %s to complete [loop %i]",
-                [w[0] for w in wait_on], loop_count,
+                [w[0] for w in wait_on],
+                loop_count,
             )
             with PreserveLoggingContext():
                 yield defer.DeferredList((w[1] for w in wait_on))
@@ -279,13 +269,6 @@ class Keyring(object):
             verify_requests (list[VerifyKeyRequest]): list of verify requests
         """
 
-        # These are functions that produce keys given a list of key ids
-        key_fetch_fns = (
-            self.get_keys_from_store,  # First try the local store
-            self.get_keys_from_perspectives,  # Then try via perspectives
-            self.get_keys_from_server,  # Then try directly
-        )
-
         @defer.inlineCallbacks
         def do_iterations():
             with Measure(self.clock, "get_server_verify_keys"):
@@ -296,8 +279,8 @@ class Keyring(object):
                         verify_request.key_ids
                     )
 
-                for fn in key_fetch_fns:
-                    results = yield fn(missing_keys.items())
+                for f in self._key_fetchers:
+                    results = yield f.get_keys(missing_keys.items())
 
                     # We now need to figure out which verify requests we have keys
                     # for and which we don't
@@ -315,11 +298,15 @@ class Keyring(object):
                         # complete this VerifyKeyRequest.
                         result_keys = results.get(server_name, {})
                         for key_id in verify_request.key_ids:
-                            key = result_keys.get(key_id)
-                            if key:
+                            fetch_key_result = result_keys.get(key_id)
+                            if fetch_key_result:
                                 with PreserveLoggingContext():
                                     verify_request.deferred.callback(
-                                        (server_name, key_id, key)
+                                        (
+                                            server_name,
+                                            key_id,
+                                            fetch_key_result.verify_key,
+                                        )
                                     )
                                 break
                         else:
@@ -335,13 +322,14 @@ class Keyring(object):
 
                 with PreserveLoggingContext():
                     for verify_request in requests_missing_keys:
-                        verify_request.deferred.errback(SynapseError(
-                            401,
-                            "No key for %s with id %s" % (
-                                verify_request.server_name, verify_request.key_ids,
-                            ),
-                            Codes.UNAUTHORIZED,
-                        ))
+                        verify_request.deferred.errback(
+                            SynapseError(
+                                401,
+                                "No key for %s with id %s"
+                                % (verify_request.server_name, verify_request.key_ids),
+                                Codes.UNAUTHORIZED,
+                            )
+                        )
 
         def on_err(err):
             with PreserveLoggingContext():
@@ -351,17 +339,30 @@ class Keyring(object):
 
         run_in_background(do_iterations).addErrback(on_err)
 
-    @defer.inlineCallbacks
-    def get_keys_from_store(self, server_name_and_key_ids):
+
+class KeyFetcher(object):
+    def get_keys(self, server_name_and_key_ids):
         """
         Args:
-            server_name_and_key_ids (iterable(Tuple[str, iterable[str]]):
+            server_name_and_key_ids (iterable[Tuple[str, iterable[str]]]):
                 list of (server_name, iterable[key_id]) tuples to fetch keys for
 
         Returns:
-            Deferred: resolves to dict[str, dict[str, VerifyKey|None]]: map from
-                server_name -> key_id -> VerifyKey
+            Deferred[dict[str, dict[str, synapse.storage.keys.FetchKeyResult|None]]]:
+                map from server_name -> key_id -> FetchKeyResult
         """
+        raise NotImplementedError
+
+
+class StoreKeyFetcher(KeyFetcher):
+    """KeyFetcher impl which fetches keys from our data store"""
+
+    def __init__(self, hs):
+        self.store = hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def get_keys(self, server_name_and_key_ids):
+        """see KeyFetcher.get_keys"""
         keys_to_fetch = (
             (server_name, key_id)
             for server_name, key_ids in server_name_and_key_ids
@@ -373,8 +374,127 @@ class Keyring(object):
             keys.setdefault(server_name, {})[key_id] = key
         defer.returnValue(keys)
 
+
+class BaseV2KeyFetcher(object):
+    def __init__(self, hs):
+        self.store = hs.get_datastore()
+        self.config = hs.get_config()
+
     @defer.inlineCallbacks
-    def get_keys_from_perspectives(self, server_name_and_key_ids):
+    def process_v2_response(
+        self, from_server, response_json, time_added_ms, requested_ids=[]
+    ):
+        """Parse a 'Server Keys' structure from the result of a /key request
+
+        This is used to parse either the entirety of the response from
+        GET /_matrix/key/v2/server, or a single entry from the list returned by
+        POST /_matrix/key/v2/query.
+
+        Checks that each signature in the response that claims to come from the origin
+        server is valid. (Does not check that there actually is such a signature, for
+        some reason.)
+
+        Stores the json in server_keys_json so that it can be used for future responses
+        to /_matrix/key/v2/query.
+
+        Args:
+            from_server (str): the name of the server producing this result: either
+                the origin server for a /_matrix/key/v2/server request, or the notary
+                for a /_matrix/key/v2/query.
+
+            response_json (dict): the json-decoded Server Keys response object
+
+            time_added_ms (int): the timestamp to record in server_keys_json
+
+            requested_ids (iterable[str]): a list of the key IDs that were requested.
+                We will store the json for these key ids as well as any that are
+                actually in the response
+
+        Returns:
+            Deferred[dict[str, FetchKeyResult]]: map from key_id to result object
+        """
+        ts_valid_until_ms = response_json[u"valid_until_ts"]
+
+        # start by extracting the keys from the response, since they may be required
+        # to validate the signature on the response.
+        verify_keys = {}
+        for key_id, key_data in response_json["verify_keys"].items():
+            if is_signing_algorithm_supported(key_id):
+                key_base64 = key_data["key"]
+                key_bytes = decode_base64(key_base64)
+                verify_key = decode_verify_key_bytes(key_id, key_bytes)
+                verify_keys[key_id] = FetchKeyResult(
+                    verify_key=verify_key, valid_until_ts=ts_valid_until_ms
+                )
+
+        # TODO: improve this signature checking
+        server_name = response_json["server_name"]
+        for key_id in response_json["signatures"].get(server_name, {}):
+            if key_id not in verify_keys:
+                raise KeyLookupError(
+                    "Key response must include verification keys for all signatures"
+                )
+
+            verify_signed_json(
+                response_json, server_name, verify_keys[key_id].verify_key
+            )
+
+        for key_id, key_data in response_json["old_verify_keys"].items():
+            if is_signing_algorithm_supported(key_id):
+                key_base64 = key_data["key"]
+                key_bytes = decode_base64(key_base64)
+                verify_key = decode_verify_key_bytes(key_id, key_bytes)
+                verify_keys[key_id] = FetchKeyResult(
+                    verify_key=verify_key, valid_until_ts=key_data["expired_ts"]
+                )
+
+        # re-sign the json with our own key, so that it is ready if we are asked to
+        # give it out as a notary server
+        signed_key_json = sign_json(
+            response_json, self.config.server_name, self.config.signing_key[0]
+        )
+
+        signed_key_json_bytes = encode_canonical_json(signed_key_json)
+
+        # for reasons I don't quite understand, we store this json for the key ids we
+        # requested, as well as those we got.
+        updated_key_ids = set(requested_ids)
+        updated_key_ids.update(verify_keys)
+
+        yield logcontext.make_deferred_yieldable(
+            defer.gatherResults(
+                [
+                    run_in_background(
+                        self.store.store_server_keys_json,
+                        server_name=server_name,
+                        key_id=key_id,
+                        from_server=from_server,
+                        ts_now_ms=time_added_ms,
+                        ts_expires_ms=ts_valid_until_ms,
+                        key_json_bytes=signed_key_json_bytes,
+                    )
+                    for key_id in updated_key_ids
+                ],
+                consumeErrors=True,
+            ).addErrback(unwrapFirstError)
+        )
+
+        defer.returnValue(verify_keys)
+
+
+class PerspectivesKeyFetcher(BaseV2KeyFetcher):
+    """KeyFetcher impl which fetches keys from the "perspectives" servers"""
+
+    def __init__(self, hs):
+        super(PerspectivesKeyFetcher, self).__init__(hs)
+        self.clock = hs.get_clock()
+        self.client = hs.get_http_client()
+        self.perspective_servers = self.config.perspectives
+
+    @defer.inlineCallbacks
+    def get_keys(self, server_name_and_key_ids):
+        """see KeyFetcher.get_keys"""
+
         @defer.inlineCallbacks
         def get_key(perspective_name, perspective_keys):
             try:
@@ -383,25 +503,26 @@ class Keyring(object):
                 )
                 defer.returnValue(result)
             except KeyLookupError as e:
-                logger.warning(
-                    "Key lookup failed from %r: %s", perspective_name, e,
-                )
+                logger.warning("Key lookup failed from %r: %s", perspective_name, e)
             except Exception as e:
                 logger.exception(
                     "Unable to get key from %r: %s %s",
                     perspective_name,
-                    type(e).__name__, str(e),
+                    type(e).__name__,
+                    str(e),
                 )
 
             defer.returnValue({})
 
-        results = yield logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                run_in_background(get_key, p_name, p_keys)
-                for p_name, p_keys in self.perspective_servers.items()
-            ],
-            consumeErrors=True,
-        ).addErrback(unwrapFirstError))
+        results = yield logcontext.make_deferred_yieldable(
+            defer.gatherResults(
+                [
+                    run_in_background(get_key, p_name, p_keys)
+                    for p_name, p_keys in self.perspective_servers.items()
+                ],
+                consumeErrors=True,
+            ).addErrback(unwrapFirstError)
+        )
 
         union_of_keys = {}
         for result in results:
@@ -411,33 +532,21 @@ class Keyring(object):
         defer.returnValue(union_of_keys)
 
     @defer.inlineCallbacks
-    def get_keys_from_server(self, server_name_and_key_ids):
-        results = yield logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                run_in_background(
-                    self.get_server_verify_key_v2_direct,
-                    server_name,
-                    key_ids,
-                )
-                for server_name, key_ids in server_name_and_key_ids
-            ],
-            consumeErrors=True,
-        ).addErrback(unwrapFirstError))
-
-        merged = {}
-        for result in results:
-            merged.update(result)
-
-        defer.returnValue({
-            server_name: keys
-            for server_name, keys in merged.items()
-            if keys
-        })
+    def get_server_verify_key_v2_indirect(
+        self, server_names_and_key_ids, perspective_name, perspective_keys
+    ):
+        """
+        Args:
+            server_names_and_key_ids (iterable[Tuple[str, iterable[str]]]):
+                list of (server_name, iterable[key_id]) tuples to fetch keys for
+            perspective_name (str): name of the notary server to query for the keys
+            perspective_keys (dict[str, VerifyKey]): map of key_id->key for the
+                notary server
 
-    @defer.inlineCallbacks
-    def get_server_verify_key_v2_indirect(self, server_names_and_key_ids,
-                                          perspective_name,
-                                          perspective_keys):
+        Returns:
+            Deferred[dict[str, dict[str, synapse.storage.keys.FetchKeyResult]]]: map
+                from server_name -> key_id -> FetchKeyResult
+        """
         # TODO(mark): Set the minimum_valid_until_ts to that needed by
         # the events being validated or the current time if validating
         # an incoming request.
@@ -448,9 +557,7 @@ class Keyring(object):
                 data={
                     u"server_keys": {
                         server_name: {
-                            key_id: {
-                                u"minimum_valid_until_ts": 0
-                            } for key_id in key_ids
+                            key_id: {u"minimum_valid_until_ts": 0} for key_id in key_ids
                         }
                         for server_name, key_ids in server_names_and_key_ids
                     }
@@ -458,21 +565,20 @@ class Keyring(object):
                 long_retries=True,
             )
         except (NotRetryingDestination, RequestSendFailed) as e:
-            raise_from(
-                KeyLookupError("Failed to connect to remote server"), e,
-            )
+            raise_from(KeyLookupError("Failed to connect to remote server"), e)
         except HttpResponseException as e:
-            raise_from(
-                KeyLookupError("Remote server returned an error"), e,
-            )
+            raise_from(KeyLookupError("Remote server returned an error"), e)
 
         keys = {}
+        added_keys = []
 
-        responses = query_response["server_keys"]
+        time_now_ms = self.clock.time_msec()
 
-        for response in responses:
-            if (u"signatures" not in response
-                    or perspective_name not in response[u"signatures"]):
+        for response in query_response["server_keys"]:
+            if (
+                u"signatures" not in response
+                or perspective_name not in response[u"signatures"]
+            ):
                 raise KeyLookupError(
                     "Key response not signed by perspective server"
                     " %r" % (perspective_name,)
@@ -482,9 +588,7 @@ class Keyring(object):
             for key_id in response[u"signatures"][perspective_name]:
                 if key_id in perspective_keys:
                     verify_signed_json(
-                        response,
-                        perspective_name,
-                        perspective_keys[key_id]
+                        response, perspective_name, perspective_keys[key_id]
                     )
                     verified = True
 
@@ -494,7 +598,7 @@ class Keyring(object):
                     " known key, signed with: %r, known keys: %r",
                     perspective_name,
                     list(response[u"signatures"][perspective_name]),
-                    list(perspective_keys)
+                    list(perspective_keys),
                 )
                 raise KeyLookupError(
                     "Response not signed with a known key for perspective"
@@ -502,196 +606,101 @@ class Keyring(object):
                 )
 
             processed_response = yield self.process_v2_response(
-                perspective_name, response
+                perspective_name, response, time_added_ms=time_now_ms
             )
             server_name = response["server_name"]
 
+            added_keys.extend(
+                (server_name, key_id, key) for key_id, key in processed_response.items()
+            )
             keys.setdefault(server_name, {}).update(processed_response)
 
-        yield logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                run_in_background(
-                    self.store_keys,
-                    server_name=server_name,
-                    from_server=perspective_name,
-                    verify_keys=response_keys,
-                )
-                for server_name, response_keys in keys.items()
-            ],
-            consumeErrors=True
-        ).addErrback(unwrapFirstError))
+        yield self.store.store_server_verify_keys(
+            perspective_name, time_now_ms, added_keys
+        )
 
         defer.returnValue(keys)
 
+
+class ServerKeyFetcher(BaseV2KeyFetcher):
+    """KeyFetcher impl which fetches keys from the origin servers"""
+
+    def __init__(self, hs):
+        super(ServerKeyFetcher, self).__init__(hs)
+        self.clock = hs.get_clock()
+        self.client = hs.get_http_client()
+
+    @defer.inlineCallbacks
+    def get_keys(self, server_name_and_key_ids):
+        """see KeyFetcher.get_keys"""
+        results = yield logcontext.make_deferred_yieldable(
+            defer.gatherResults(
+                [
+                    run_in_background(
+                        self.get_server_verify_key_v2_direct, server_name, key_ids
+                    )
+                    for server_name, key_ids in server_name_and_key_ids
+                ],
+                consumeErrors=True,
+            ).addErrback(unwrapFirstError)
+        )
+
+        merged = {}
+        for result in results:
+            merged.update(result)
+
+        defer.returnValue(
+            {server_name: keys for server_name, keys in merged.items() if keys}
+        )
+
     @defer.inlineCallbacks
     def get_server_verify_key_v2_direct(self, server_name, key_ids):
-        keys = {}  # type: dict[str, nacl.signing.VerifyKey]
+        keys = {}  # type: dict[str, FetchKeyResult]
 
         for requested_key_id in key_ids:
             if requested_key_id in keys:
                 continue
 
+            time_now_ms = self.clock.time_msec()
             try:
                 response = yield self.client.get_json(
                     destination=server_name,
-                    path="/_matrix/key/v2/server/" + urllib.parse.quote(requested_key_id),
+                    path="/_matrix/key/v2/server/"
+                    + urllib.parse.quote(requested_key_id),
                     ignore_backoff=True,
                 )
             except (NotRetryingDestination, RequestSendFailed) as e:
-                raise_from(
-                    KeyLookupError("Failed to connect to remote server"), e,
-                )
+                raise_from(KeyLookupError("Failed to connect to remote server"), e)
             except HttpResponseException as e:
-                raise_from(
-                    KeyLookupError("Remote server returned an error"), e,
-                )
+                raise_from(KeyLookupError("Remote server returned an error"), e)
 
-            if (u"signatures" not in response
-                    or server_name not in response[u"signatures"]):
+            if (
+                u"signatures" not in response
+                or server_name not in response[u"signatures"]
+            ):
                 raise KeyLookupError("Key response not signed by remote server")
 
             if response["server_name"] != server_name:
-                raise KeyLookupError("Expected a response for server %r not %r" % (
-                    server_name, response["server_name"]
-                ))
+                raise KeyLookupError(
+                    "Expected a response for server %r not %r"
+                    % (server_name, response["server_name"])
+                )
 
             response_keys = yield self.process_v2_response(
                 from_server=server_name,
                 requested_ids=[requested_key_id],
                 response_json=response,
+                time_added_ms=time_now_ms,
+            )
+            yield self.store.store_server_verify_keys(
+                server_name,
+                time_now_ms,
+                ((server_name, key_id, key) for key_id, key in response_keys.items()),
             )
-
             keys.update(response_keys)
 
-        yield self.store_keys(
-            server_name=server_name,
-            from_server=server_name,
-            verify_keys=keys,
-        )
         defer.returnValue({server_name: keys})
 
-    @defer.inlineCallbacks
-    def process_v2_response(
-        self, from_server, response_json, requested_ids=[],
-    ):
-        """Parse a 'Server Keys' structure from the result of a /key request
-
-        This is used to parse either the entirety of the response from
-        GET /_matrix/key/v2/server, or a single entry from the list returned by
-        POST /_matrix/key/v2/query.
-
-        Checks that each signature in the response that claims to come from the origin
-        server is valid. (Does not check that there actually is such a signature, for
-        some reason.)
-
-        Stores the json in server_keys_json so that it can be used for future responses
-        to /_matrix/key/v2/query.
-
-        Args:
-            from_server (str): the name of the server producing this result: either
-                the origin server for a /_matrix/key/v2/server request, or the notary
-                for a /_matrix/key/v2/query.
-
-            response_json (dict): the json-decoded Server Keys response object
-
-            requested_ids (iterable[str]): a list of the key IDs that were requested.
-                We will store the json for these key ids as well as any that are
-                actually in the response
-
-        Returns:
-            Deferred[dict[str, nacl.signing.VerifyKey]]:
-                map from key_id to key object
-        """
-        time_now_ms = self.clock.time_msec()
-        response_keys = {}
-        verify_keys = {}
-        for key_id, key_data in response_json["verify_keys"].items():
-            if is_signing_algorithm_supported(key_id):
-                key_base64 = key_data["key"]
-                key_bytes = decode_base64(key_base64)
-                verify_key = decode_verify_key_bytes(key_id, key_bytes)
-                verify_key.time_added = time_now_ms
-                verify_keys[key_id] = verify_key
-
-        old_verify_keys = {}
-        for key_id, key_data in response_json["old_verify_keys"].items():
-            if is_signing_algorithm_supported(key_id):
-                key_base64 = key_data["key"]
-                key_bytes = decode_base64(key_base64)
-                verify_key = decode_verify_key_bytes(key_id, key_bytes)
-                verify_key.expired = key_data["expired_ts"]
-                verify_key.time_added = time_now_ms
-                old_verify_keys[key_id] = verify_key
-
-        server_name = response_json["server_name"]
-        for key_id in response_json["signatures"].get(server_name, {}):
-            if key_id not in response_json["verify_keys"]:
-                raise KeyLookupError(
-                    "Key response must include verification keys for all"
-                    " signatures"
-                )
-            if key_id in verify_keys:
-                verify_signed_json(
-                    response_json,
-                    server_name,
-                    verify_keys[key_id]
-                )
-
-        signed_key_json = sign_json(
-            response_json,
-            self.config.server_name,
-            self.config.signing_key[0],
-        )
-
-        signed_key_json_bytes = encode_canonical_json(signed_key_json)
-        ts_valid_until_ms = signed_key_json[u"valid_until_ts"]
-
-        updated_key_ids = set(requested_ids)
-        updated_key_ids.update(verify_keys)
-        updated_key_ids.update(old_verify_keys)
-
-        response_keys.update(verify_keys)
-        response_keys.update(old_verify_keys)
-
-        yield logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                run_in_background(
-                    self.store.store_server_keys_json,
-                    server_name=server_name,
-                    key_id=key_id,
-                    from_server=from_server,
-                    ts_now_ms=time_now_ms,
-                    ts_expires_ms=ts_valid_until_ms,
-                    key_json_bytes=signed_key_json_bytes,
-                )
-                for key_id in updated_key_ids
-            ],
-            consumeErrors=True,
-        ).addErrback(unwrapFirstError))
-
-        defer.returnValue(response_keys)
-
-    def store_keys(self, server_name, from_server, verify_keys):
-        """Store a collection of verify keys for a given server
-        Args:
-            server_name(str): The name of the server the keys are for.
-            from_server(str): The server the keys were downloaded from.
-            verify_keys(dict): A mapping of key_id to VerifyKey.
-        Returns:
-            A deferred that completes when the keys are stored.
-        """
-        # TODO(markjh): Store whether the keys have expired.
-        return logcontext.make_deferred_yieldable(defer.gatherResults(
-            [
-                run_in_background(
-                    self.store.store_server_verify_key,
-                    server_name, server_name, key.time_added, key
-                )
-                for key_id, key in verify_keys.items()
-            ],
-            consumeErrors=True,
-        ).addErrback(unwrapFirstError))
-
 
 @defer.inlineCallbacks
 def _handle_key_deferred(verify_request):
@@ -713,17 +722,19 @@ def _handle_key_deferred(verify_request):
     except KeyLookupError as e:
         logger.warn(
             "Failed to download keys for %s: %s %s",
-            server_name, type(e).__name__, str(e),
+            server_name,
+            type(e).__name__,
+            str(e),
         )
         raise SynapseError(
-            502,
-            "Error downloading keys for %s" % (server_name,),
-            Codes.UNAUTHORIZED,
+            502, "Error downloading keys for %s" % (server_name,), Codes.UNAUTHORIZED
         )
     except Exception as e:
         logger.exception(
             "Got Exception when downloading keys for %s: %s %s",
-            server_name, type(e).__name__, str(e),
+            server_name,
+            type(e).__name__,
+            str(e),
         )
         raise SynapseError(
             401,
@@ -733,22 +744,24 @@ def _handle_key_deferred(verify_request):
 
     json_object = verify_request.json_object
 
-    logger.debug("Got key %s %s:%s for server %s, verifying" % (
-        key_id, verify_key.alg, verify_key.version, server_name,
-    ))
+    logger.debug(
+        "Got key %s %s:%s for server %s, verifying"
+        % (key_id, verify_key.alg, verify_key.version, server_name)
+    )
     try:
         verify_signed_json(json_object, server_name, verify_key)
     except SignatureVerifyException as e:
         logger.debug(
             "Error verifying signature for %s:%s:%s with key %s: %s",
-            server_name, verify_key.alg, verify_key.version,
+            server_name,
+            verify_key.alg,
+            verify_key.version,
             encode_verify_key_base64(verify_key),
             str(e),
         )
         raise SynapseError(
             401,
-            "Invalid signature for server %s with key %s:%s: %s" % (
-                server_name, verify_key.alg, verify_key.version, str(e),
-            ),
+            "Invalid signature for server %s with key %s:%s: %s"
+            % (server_name, verify_key.alg, verify_key.version, str(e)),
             Codes.UNAUTHORIZED,
         )
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 12056d5be2..1edd19cc13 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -21,6 +21,7 @@ import six
 
 from unpaddedbase64 import encode_base64
 
+from synapse.api.errors import UnsupportedRoomVersionError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, EventFormatVersions
 from synapse.util.caches import intern_dict
 from synapse.util.frozenutils import freeze
@@ -335,13 +336,32 @@ class FrozenEventV2(EventBase):
         return self.__repr__()
 
     def __repr__(self):
-        return "<FrozenEventV2 event_id='%s', type='%s', state_key='%s'>" % (
+        return "<%s event_id='%s', type='%s', state_key='%s'>" % (
+            self.__class__.__name__,
             self.event_id,
             self.get("type", None),
             self.get("state_key", None),
         )
 
 
+class FrozenEventV3(FrozenEventV2):
+    """FrozenEventV3, which differs from FrozenEventV2 only in the event_id format"""
+    format_version = EventFormatVersions.V3  # All events of this type are V3
+
+    @property
+    def event_id(self):
+        # We have to import this here as otherwise we get an import loop which
+        # is hard to break.
+        from synapse.crypto.event_signing import compute_event_reference_hash
+
+        if self._event_id:
+            return self._event_id
+        self._event_id = "$" + encode_base64(
+            compute_event_reference_hash(self)[1], urlsafe=True
+        )
+        return self._event_id
+
+
 def room_version_to_event_format(room_version):
     """Converts a room version string to the event format
 
@@ -350,12 +370,15 @@ def room_version_to_event_format(room_version):
 
     Returns:
         int
+
+    Raises:
+        UnsupportedRoomVersionError if the room version is unknown
     """
     v = KNOWN_ROOM_VERSIONS.get(room_version)
 
     if not v:
-        # We should have already checked version, so this should not happen
-        raise RuntimeError("Unrecognized room version %s" % (room_version,))
+        # this can happen if support is withdrawn for a room version
+        raise UnsupportedRoomVersionError()
 
     return v.event_format
 
@@ -376,6 +399,8 @@ def event_type_from_format_version(format_version):
         return FrozenEvent
     elif format_version == EventFormatVersions.V2:
         return FrozenEventV2
+    elif format_version == EventFormatVersions.V3:
+        return FrozenEventV3
     else:
         raise Exception(
             "No event format %r" % (format_version,)
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index fba27177c7..546b6f4982 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -18,6 +18,7 @@ import attr
 from twisted.internet import defer
 
 from synapse.api.constants import MAX_DEPTH
+from synapse.api.errors import UnsupportedRoomVersionError
 from synapse.api.room_versions import (
     KNOWN_EVENT_FORMAT_VERSIONS,
     KNOWN_ROOM_VERSIONS,
@@ -75,6 +76,7 @@ class EventBuilder(object):
     # someone tries to get them when they don't exist.
     _state_key = attr.ib(default=None)
     _redacts = attr.ib(default=None)
+    _origin_server_ts = attr.ib(default=None)
 
     internal_metadata = attr.ib(default=attr.Factory(lambda: _EventInternalMetadata({})))
 
@@ -141,6 +143,9 @@ class EventBuilder(object):
         if self._redacts is not None:
             event_dict["redacts"] = self._redacts
 
+        if self._origin_server_ts is not None:
+            event_dict["origin_server_ts"] = self._origin_server_ts
+
         defer.returnValue(
             create_local_event_from_event_dict(
                 clock=self._clock,
@@ -178,9 +183,8 @@ class EventBuilderFactory(object):
         """
         v = KNOWN_ROOM_VERSIONS.get(room_version)
         if not v:
-            raise Exception(
-                "No event format defined for version %r" % (room_version,)
-            )
+            # this can happen if support is withdrawn for a room version
+            raise UnsupportedRoomVersionError()
         return self.for_room_version(v, key_values)
 
     def for_room_version(self, room_version, key_values):
@@ -209,6 +213,7 @@ class EventBuilderFactory(object):
             content=key_values.get("content", {}),
             unsigned=key_values.get("unsigned", {}),
             redacts=key_values.get("redacts", None),
+            origin_server_ts=key_values.get("origin_server_ts", None),
         )
 
 
@@ -245,7 +250,7 @@ def create_local_event_from_event_dict(clock, hostname, signing_key,
         event_dict["event_id"] = _create_event_id(clock, hostname)
 
     event_dict["origin"] = hostname
-    event_dict["origin_server_ts"] = time_now
+    event_dict.setdefault("origin_server_ts", time_now)
 
     event_dict.setdefault("unsigned", {})
     age = event_dict["unsigned"].pop("age", 0)
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index a5454556cc..e2d4384de1 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -21,7 +21,7 @@ from frozendict import frozendict
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes
+from synapse.api.constants import EventTypes, RelationTypes
 from synapse.util.async_helpers import yieldable_gather_results
 
 from . import EventBase
@@ -324,21 +324,70 @@ class EventClientSerializer(object):
     """
 
     def __init__(self, hs):
-        pass
+        self.store = hs.get_datastore()
+        self.experimental_msc1849_support_enabled = (
+            hs.config.experimental_msc1849_support_enabled
+        )
 
-    def serialize_event(self, event, time_now, **kwargs):
+    @defer.inlineCallbacks
+    def serialize_event(self, event, time_now, bundle_aggregations=True, **kwargs):
         """Serializes a single event.
 
         Args:
             event (EventBase)
             time_now (int): The current time in milliseconds
+            bundle_aggregations (bool): Whether to bundle in related events
             **kwargs: Arguments to pass to `serialize_event`
 
         Returns:
             Deferred[dict]: The serialized event
         """
-        event = serialize_event(event, time_now, **kwargs)
-        return defer.succeed(event)
+        # To handle the case of presence events and the like
+        if not isinstance(event, EventBase):
+            defer.returnValue(event)
+
+        event_id = event.event_id
+        serialized_event = serialize_event(event, time_now, **kwargs)
+
+        # If MSC1849 is enabled then we need to look if thre are any relations
+        # we need to bundle in with the event
+        if self.experimental_msc1849_support_enabled and bundle_aggregations:
+            annotations = yield self.store.get_aggregation_groups_for_event(
+                event_id,
+            )
+            references = yield self.store.get_relations_for_event(
+                event_id, RelationTypes.REFERENCE, direction="f",
+            )
+
+            if annotations.chunk:
+                r = serialized_event["unsigned"].setdefault("m.relations", {})
+                r[RelationTypes.ANNOTATION] = annotations.to_dict()
+
+            if references.chunk:
+                r = serialized_event["unsigned"].setdefault("m.relations", {})
+                r[RelationTypes.REFERENCE] = references.to_dict()
+
+            edit = None
+            if event.type == EventTypes.Message:
+                edit = yield self.store.get_applicable_edit(event_id)
+
+            if edit:
+                # If there is an edit replace the content, preserving existing
+                # relations.
+
+                relations = event.content.get("m.relates_to")
+                serialized_event["content"] = edit.content.get("m.new_content", {})
+                if relations:
+                    serialized_event["content"]["m.relates_to"] = relations
+                else:
+                    serialized_event["content"].pop("m.relates_to", None)
+
+                r = serialized_event["unsigned"].setdefault("m.relations", {})
+                r[RelationTypes.REPLACE] = {
+                    "event_id": edit.event_id,
+                }
+
+        defer.returnValue(serialized_event)
 
     def serialize_events(self, events, time_now, **kwargs):
         """Serializes multiple events.
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index df60828dba..4c28c1dc3c 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -33,6 +33,7 @@ from synapse.api.errors import (
     IncompatibleRoomVersionError,
     NotFoundError,
     SynapseError,
+    UnsupportedRoomVersionError,
 )
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.crypto.event_signing import compute_event_signature
@@ -198,11 +199,22 @@ class FederationServer(FederationBase):
 
             try:
                 room_version = yield self.store.get_room_version(room_id)
-                format_ver = room_version_to_event_format(room_version)
             except NotFoundError:
                 logger.info("Ignoring PDU for unknown room_id: %s", room_id)
                 continue
 
+            try:
+                format_ver = room_version_to_event_format(room_version)
+            except UnsupportedRoomVersionError:
+                # this can happen if support for a given room version is withdrawn,
+                # so that we still get events for said room.
+                logger.info(
+                    "Ignoring PDU for room %s with unknown version %s",
+                    room_id,
+                    room_version,
+                )
+                continue
+
             event = event_from_pdu_json(p, format_ver)
             pdus_by_room.setdefault(room_id, []).append(event)
 
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index 6003ad9cca..eb525070cf 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -122,6 +122,9 @@ class EventStreamHandler(BaseHandler):
 
             chunks = yield self._event_serializer.serialize_events(
                 events, time_now, as_client_event=as_client_event,
+                # We don't bundle "live" events, as otherwise clients
+                # will end up double counting annotations.
+                bundle_aggregations=False,
             )
 
             chunk = {
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 0684778882..cf4fad7de0 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1916,6 +1916,11 @@ class FederationHandler(BaseHandler):
                     event.room_id, latest_event_ids=extrem_ids,
                 )
 
+            logger.debug(
+                "Doing soft-fail check for %s: state %s",
+                event.event_id, current_state_ids,
+            )
+
             # Now check if event pass auth against said current state
             auth_types = auth_types_for_event(event)
             current_state_ids = [
@@ -1932,7 +1937,7 @@ class FederationHandler(BaseHandler):
                 self.auth.check(room_version, event, auth_events=current_auth_events)
             except AuthError as e:
                 logger.warn(
-                    "Failed current state auth resolution for %r because %s",
+                    "Soft-failing %r because %s",
                     event, e,
                 )
                 event.internal_metadata.soft_failed = True
@@ -2008,15 +2013,44 @@ class FederationHandler(BaseHandler):
 
         Args:
             origin (str):
-            event (synapse.events.FrozenEvent):
+            event (synapse.events.EventBase):
             context (synapse.events.snapshot.EventContext):
-            auth_events (dict[(str, str)->str]):
+            auth_events (dict[(str, str)->synapse.events.EventBase]):
+                Map from (event_type, state_key) to event
+
+                What we expect the event's auth_events to be, based on the event's
+                position in the dag. I think? maybe??
+
+                Also NB that this function adds entries to it.
+        Returns:
+            defer.Deferred[None]
+        """
+        room_version = yield self.store.get_room_version(event.room_id)
+
+        yield self._update_auth_events_and_context_for_auth(
+            origin, event, context, auth_events
+        )
+        try:
+            self.auth.check(room_version, event, auth_events=auth_events)
+        except AuthError as e:
+            logger.warn("Failed auth resolution for %r because %s", event, e)
+            raise e
+
+    @defer.inlineCallbacks
+    def _update_auth_events_and_context_for_auth(
+        self, origin, event, context, auth_events
+    ):
+        """Helper for do_auth. See there for docs.
+
+        Args:
+            origin (str):
+            event (synapse.events.EventBase):
+            context (synapse.events.snapshot.EventContext):
+            auth_events (dict[(str, str)->synapse.events.EventBase]):
 
         Returns:
             defer.Deferred[None]
         """
-        # Check if we have all the auth events.
-        current_state = set(e.event_id for e in auth_events.values())
         event_auth_events = set(event.auth_event_ids())
 
         if event.is_state():
@@ -2024,11 +2058,21 @@ class FederationHandler(BaseHandler):
         else:
             event_key = None
 
-        if event_auth_events - current_state:
+        # if the event's auth_events refers to events which are not in our
+        # calculated auth_events, we need to fetch those events from somewhere.
+        #
+        # we start by fetching them from the store, and then try calling /event_auth/.
+        missing_auth = event_auth_events.difference(
+            e.event_id for e in auth_events.values()
+        )
+
+        if missing_auth:
             # TODO: can we use store.have_seen_events here instead?
             have_events = yield self.store.get_seen_events_with_rejections(
-                event_auth_events - current_state
+                missing_auth
             )
+            logger.debug("Got events %s from store", have_events)
+            missing_auth.difference_update(have_events.keys())
         else:
             have_events = {}
 
@@ -2037,13 +2081,12 @@ class FederationHandler(BaseHandler):
             for e in auth_events.values()
         })
 
-        seen_events = set(have_events.keys())
-
-        missing_auth = event_auth_events - seen_events - current_state
-
         if missing_auth:
-            logger.info("Missing auth: %s", missing_auth)
             # If we don't have all the auth events, we need to get them.
+            logger.info(
+                "auth_events contains unknown events: %s",
+                missing_auth,
+            )
             try:
                 remote_auth_chain = yield self.federation_client.get_event_auth(
                     origin, event.room_id, event.event_id
@@ -2084,145 +2127,168 @@ class FederationHandler(BaseHandler):
                 have_events = yield self.store.get_seen_events_with_rejections(
                     event.auth_event_ids()
                 )
-                seen_events = set(have_events.keys())
             except Exception:
                 # FIXME:
                 logger.exception("Failed to get auth chain")
 
+        if event.internal_metadata.is_outlier():
+            logger.info("Skipping auth_event fetch for outlier")
+            return
+
         # FIXME: Assumes we have and stored all the state for all the
         # prev_events
-        current_state = set(e.event_id for e in auth_events.values())
-        different_auth = event_auth_events - current_state
+        different_auth = event_auth_events.difference(
+            e.event_id for e in auth_events.values()
+        )
 
-        room_version = yield self.store.get_room_version(event.room_id)
+        if not different_auth:
+            return
 
-        if different_auth and not event.internal_metadata.is_outlier():
-            # Do auth conflict res.
-            logger.info("Different auth: %s", different_auth)
-
-            different_events = yield logcontext.make_deferred_yieldable(
-                defer.gatherResults([
-                    logcontext.run_in_background(
-                        self.store.get_event,
-                        d,
-                        allow_none=True,
-                        allow_rejected=False,
-                    )
-                    for d in different_auth
-                    if d in have_events and not have_events[d]
-                ], consumeErrors=True)
-            ).addErrback(unwrapFirstError)
-
-            if different_events:
-                local_view = dict(auth_events)
-                remote_view = dict(auth_events)
-                remote_view.update({
-                    (d.type, d.state_key): d for d in different_events if d
-                })
+        logger.info(
+            "auth_events refers to events which are not in our calculated auth "
+            "chain: %s",
+            different_auth,
+        )
 
-                new_state = yield self.state_handler.resolve_events(
-                    room_version,
-                    [list(local_view.values()), list(remote_view.values())],
-                    event
+        room_version = yield self.store.get_room_version(event.room_id)
+
+        different_events = yield logcontext.make_deferred_yieldable(
+            defer.gatherResults([
+                logcontext.run_in_background(
+                    self.store.get_event,
+                    d,
+                    allow_none=True,
+                    allow_rejected=False,
                 )
+                for d in different_auth
+                if d in have_events and not have_events[d]
+            ], consumeErrors=True)
+        ).addErrback(unwrapFirstError)
+
+        if different_events:
+            local_view = dict(auth_events)
+            remote_view = dict(auth_events)
+            remote_view.update({
+                (d.type, d.state_key): d for d in different_events if d
+            })
 
-                auth_events.update(new_state)
+            new_state = yield self.state_handler.resolve_events(
+                room_version,
+                [list(local_view.values()), list(remote_view.values())],
+                event
+            )
 
-                current_state = set(e.event_id for e in auth_events.values())
-                different_auth = event_auth_events - current_state
+            logger.info(
+                "After state res: updating auth_events with new state %s",
+                {
+                    (d.type, d.state_key): d.event_id for d in new_state.values()
+                    if auth_events.get((d.type, d.state_key)) != d
+                },
+            )
 
-                yield self._update_context_for_auth_events(
-                    event, context, auth_events, event_key,
-                )
+            auth_events.update(new_state)
 
-        if different_auth and not event.internal_metadata.is_outlier():
-            logger.info("Different auth after resolution: %s", different_auth)
+            different_auth = event_auth_events.difference(
+                e.event_id for e in auth_events.values()
+            )
 
-            # Only do auth resolution if we have something new to say.
-            # We can't rove an auth failure.
-            do_resolution = False
+            yield self._update_context_for_auth_events(
+                event, context, auth_events, event_key,
+            )
 
-            provable = [
-                RejectedReason.NOT_ANCESTOR, RejectedReason.NOT_ANCESTOR,
-            ]
+        if not different_auth:
+            # we're done
+            return
 
-            for e_id in different_auth:
-                if e_id in have_events:
-                    if have_events[e_id] in provable:
-                        do_resolution = True
-                        break
+        logger.info(
+            "auth_events still refers to events which are not in the calculated auth "
+            "chain after state resolution: %s",
+            different_auth,
+        )
 
-            if do_resolution:
-                prev_state_ids = yield context.get_prev_state_ids(self.store)
-                # 1. Get what we think is the auth chain.
-                auth_ids = yield self.auth.compute_auth_events(
-                    event, prev_state_ids
-                )
-                local_auth_chain = yield self.store.get_auth_chain(
-                    auth_ids, include_given=True
-                )
+        # Only do auth resolution if we have something new to say.
+        # We can't prove an auth failure.
+        do_resolution = False
 
-                try:
-                    # 2. Get remote difference.
-                    result = yield self.federation_client.query_auth(
-                        origin,
-                        event.room_id,
-                        event.event_id,
-                        local_auth_chain,
-                    )
+        for e_id in different_auth:
+            if e_id in have_events:
+                if have_events[e_id] == RejectedReason.NOT_ANCESTOR:
+                    do_resolution = True
+                    break
 
-                    seen_remotes = yield self.store.have_seen_events(
-                        [e.event_id for e in result["auth_chain"]]
-                    )
+        if not do_resolution:
+            logger.info(
+                "Skipping auth resolution due to lack of provable rejection reasons"
+            )
+            return
 
-                    # 3. Process any remote auth chain events we haven't seen.
-                    for ev in result["auth_chain"]:
-                        if ev.event_id in seen_remotes:
-                            continue
+        logger.info("Doing auth resolution")
 
-                        if ev.event_id == event.event_id:
-                            continue
+        prev_state_ids = yield context.get_prev_state_ids(self.store)
 
-                        try:
-                            auth_ids = ev.auth_event_ids()
-                            auth = {
-                                (e.type, e.state_key): e
-                                for e in result["auth_chain"]
-                                if e.event_id in auth_ids
-                                or event.type == EventTypes.Create
-                            }
-                            ev.internal_metadata.outlier = True
+        # 1. Get what we think is the auth chain.
+        auth_ids = yield self.auth.compute_auth_events(
+            event, prev_state_ids
+        )
+        local_auth_chain = yield self.store.get_auth_chain(
+            auth_ids, include_given=True
+        )
 
-                            logger.debug(
-                                "do_auth %s different_auth: %s",
-                                event.event_id, e.event_id
-                            )
+        try:
+            # 2. Get remote difference.
+            result = yield self.federation_client.query_auth(
+                origin,
+                event.room_id,
+                event.event_id,
+                local_auth_chain,
+            )
 
-                            yield self._handle_new_event(
-                                origin, ev, auth_events=auth
-                            )
+            seen_remotes = yield self.store.have_seen_events(
+                [e.event_id for e in result["auth_chain"]]
+            )
 
-                            if ev.event_id in event_auth_events:
-                                auth_events[(ev.type, ev.state_key)] = ev
-                        except AuthError:
-                            pass
+            # 3. Process any remote auth chain events we haven't seen.
+            for ev in result["auth_chain"]:
+                if ev.event_id in seen_remotes:
+                    continue
 
-                except Exception:
-                    # FIXME:
-                    logger.exception("Failed to query auth chain")
+                if ev.event_id == event.event_id:
+                    continue
 
-                # 4. Look at rejects and their proofs.
-                # TODO.
+                try:
+                    auth_ids = ev.auth_event_ids()
+                    auth = {
+                        (e.type, e.state_key): e
+                        for e in result["auth_chain"]
+                        if e.event_id in auth_ids
+                        or event.type == EventTypes.Create
+                    }
+                    ev.internal_metadata.outlier = True
+
+                    logger.debug(
+                        "do_auth %s different_auth: %s",
+                        event.event_id, e.event_id
+                    )
 
-                yield self._update_context_for_auth_events(
-                    event, context, auth_events, event_key,
-                )
+                    yield self._handle_new_event(
+                        origin, ev, auth_events=auth
+                    )
 
-        try:
-            self.auth.check(room_version, event, auth_events=auth_events)
-        except AuthError as e:
-            logger.warn("Failed auth resolution for %r because %s", event, e)
-            raise e
+                    if ev.event_id in event_auth_events:
+                        auth_events[(ev.type, ev.state_key)] = ev
+                except AuthError:
+                    pass
+
+        except Exception:
+            # FIXME:
+            logger.exception("Failed to query auth chain")
+
+        # 4. Look at rejects and their proofs.
+        # TODO.
+
+        yield self._update_context_for_auth_events(
+            event, context, auth_events, event_key,
+        )
 
     @defer.inlineCallbacks
     def _update_context_for_auth_events(self, event, context, auth_events,
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 7b2c33a922..0b02469ceb 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -22,7 +22,7 @@ from canonicaljson import encode_canonical_json, json
 from twisted.internet import defer
 from twisted.internet.defer import succeed
 
-from synapse.api.constants import EventTypes, Membership
+from synapse.api.constants import EventTypes, Membership, RelationTypes
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -166,6 +166,9 @@ class MessageHandler(object):
         now = self.clock.time_msec()
         events = yield self._event_serializer.serialize_events(
             room_state.values(), now,
+            # We don't bother bundling aggregations in when asked for state
+            # events, as clients won't use them.
+            bundle_aggregations=False,
         )
         defer.returnValue(events)
 
@@ -601,6 +604,20 @@ class EventCreationHandler(object):
 
         self.validator.validate_new(event)
 
+        # If this event is an annotation then we check that that the sender
+        # can't annotate the same way twice (e.g. stops users from liking an
+        # event multiple times).
+        relation = event.content.get("m.relates_to", {})
+        if relation.get("rel_type") == RelationTypes.ANNOTATION:
+            relates_to = relation["event_id"]
+            aggregation_key = relation["key"]
+
+            already_exists = yield self.store.has_user_annotated_event(
+                relates_to, event.type, aggregation_key, event.sender,
+            )
+            if already_exists:
+                raise SynapseError(400, "Can't send same reaction twice")
+
         logger.debug(
             "Created event %s",
             event.event_id,
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index a51d11a257..e83ee24f10 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -19,7 +19,7 @@ import logging
 from twisted.internet import defer
 
 from synapse import types
-from synapse.api.constants import LoginType
+from synapse.api.constants import MAX_USERID_LENGTH, LoginType
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -123,6 +123,15 @@ class RegistrationHandler(BaseHandler):
 
         self.check_user_id_not_appservice_exclusive(user_id)
 
+        if len(user_id) > MAX_USERID_LENGTH:
+            raise SynapseError(
+                400,
+                "User ID may not be longer than %s characters" % (
+                    MAX_USERID_LENGTH,
+                ),
+                Codes.INVALID_USERNAME
+            )
+
         users = yield self.store.get_users_by_id_case_insensitive(user_id)
         if users:
             if not guest_access_token:
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index e37ae96899..4a17911a87 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -27,7 +27,7 @@ from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, JoinRules, RoomCreationPreset
 from synapse.api.errors import AuthError, Codes, NotFoundError, StoreError, SynapseError
-from synapse.api.room_versions import DEFAULT_ROOM_VERSION, KNOWN_ROOM_VERSIONS
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.storage.state import StateFilter
 from synapse.types import RoomAlias, RoomID, RoomStreamToken, StreamToken, UserID
 from synapse.util import stringutils
@@ -70,6 +70,7 @@ class RoomCreationHandler(BaseHandler):
         self.spam_checker = hs.get_spam_checker()
         self.event_creation_handler = hs.get_event_creation_handler()
         self.room_member_handler = hs.get_room_member_handler()
+        self.config = hs.config
 
         # linearizer to stop two upgrades happening at once
         self._upgrade_linearizer = Linearizer("room_upgrade_linearizer")
@@ -475,7 +476,11 @@ class RoomCreationHandler(BaseHandler):
         if ratelimit:
             yield self.ratelimit(requester)
 
-        room_version = config.get("room_version", DEFAULT_ROOM_VERSION.identifier)
+        room_version = config.get(
+            "room_version",
+            self.config.default_room_version.identifier,
+        )
+
         if not isinstance(room_version, string_types):
             raise SynapseError(
                 400,
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index ffc588d454..93ac986c86 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -944,7 +944,7 @@ class RoomMemberHandler(object):
         }
 
         if self.config.invite_3pid_guest:
-            guest_access_token, guest_user_id = yield self.get_or_register_3pid_guest(
+            guest_user_id, guest_access_token = yield self.get_or_register_3pid_guest(
                 requester=requester,
                 medium=medium,
                 address=address,
diff --git a/synapse/handlers/stats.py b/synapse/handlers/stats.py
new file mode 100644
index 0000000000..0e92b405ba
--- /dev/null
+++ b/synapse/handlers/stats.py
@@ -0,0 +1,325 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+from twisted.internet import defer
+
+from synapse.api.constants import EventTypes, JoinRules, Membership
+from synapse.handlers.state_deltas import StateDeltasHandler
+from synapse.metrics import event_processing_positions
+from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.types import UserID
+from synapse.util.metrics import Measure
+
+logger = logging.getLogger(__name__)
+
+
+class StatsHandler(StateDeltasHandler):
+    """Handles keeping the *_stats tables updated with a simple time-series of
+    information about the users, rooms and media on the server, such that admins
+    have some idea of who is consuming their resources.
+
+    Heavily derived from UserDirectoryHandler
+    """
+
+    def __init__(self, hs):
+        super(StatsHandler, self).__init__(hs)
+        self.hs = hs
+        self.store = hs.get_datastore()
+        self.state = hs.get_state_handler()
+        self.server_name = hs.hostname
+        self.clock = hs.get_clock()
+        self.notifier = hs.get_notifier()
+        self.is_mine_id = hs.is_mine_id
+        self.stats_bucket_size = hs.config.stats_bucket_size
+
+        # The current position in the current_state_delta stream
+        self.pos = None
+
+        # Guard to ensure we only process deltas one at a time
+        self._is_processing = False
+
+        if hs.config.stats_enabled:
+            self.notifier.add_replication_callback(self.notify_new_event)
+
+            # We kick this off so that we don't have to wait for a change before
+            # we start populating stats
+            self.clock.call_later(0, self.notify_new_event)
+
+    def notify_new_event(self):
+        """Called when there may be more deltas to process
+        """
+        if not self.hs.config.stats_enabled:
+            return
+
+        if self._is_processing:
+            return
+
+        @defer.inlineCallbacks
+        def process():
+            try:
+                yield self._unsafe_process()
+            finally:
+                self._is_processing = False
+
+        self._is_processing = True
+        run_as_background_process("stats.notify_new_event", process)
+
+    @defer.inlineCallbacks
+    def _unsafe_process(self):
+        # If self.pos is None then means we haven't fetched it from DB
+        if self.pos is None:
+            self.pos = yield self.store.get_stats_stream_pos()
+
+        # If still None then the initial background update hasn't happened yet
+        if self.pos is None:
+            defer.returnValue(None)
+
+        # Loop round handling deltas until we're up to date
+        while True:
+            with Measure(self.clock, "stats_delta"):
+                deltas = yield self.store.get_current_state_deltas(self.pos)
+                if not deltas:
+                    return
+
+                logger.info("Handling %d state deltas", len(deltas))
+                yield self._handle_deltas(deltas)
+
+                self.pos = deltas[-1]["stream_id"]
+                yield self.store.update_stats_stream_pos(self.pos)
+
+                event_processing_positions.labels("stats").set(self.pos)
+
+    @defer.inlineCallbacks
+    def _handle_deltas(self, deltas):
+        """
+        Called with the state deltas to process
+        """
+        for delta in deltas:
+            typ = delta["type"]
+            state_key = delta["state_key"]
+            room_id = delta["room_id"]
+            event_id = delta["event_id"]
+            stream_id = delta["stream_id"]
+            prev_event_id = delta["prev_event_id"]
+
+            logger.debug("Handling: %r %r, %s", typ, state_key, event_id)
+
+            token = yield self.store.get_earliest_token_for_room_stats(room_id)
+
+            # If the earliest token to begin from is larger than our current
+            # stream ID, skip processing this delta.
+            if token is not None and token >= stream_id:
+                logger.debug(
+                    "Ignoring: %s as earlier than this room's initial ingestion event",
+                    event_id,
+                )
+                continue
+
+            if event_id is None and prev_event_id is None:
+                # Errr...
+                continue
+
+            event_content = {}
+
+            if event_id is not None:
+                event_content = (yield self.store.get_event(event_id)).content or {}
+
+            # quantise time to the nearest bucket
+            now = yield self.store.get_received_ts(event_id)
+            now = (now // 1000 // self.stats_bucket_size) * self.stats_bucket_size
+
+            if typ == EventTypes.Member:
+                # we could use _get_key_change here but it's a bit inefficient
+                # given we're not testing for a specific result; might as well
+                # just grab the prev_membership and membership strings and
+                # compare them.
+                prev_event_content = {}
+                if prev_event_id is not None:
+                    prev_event_content = (
+                        yield self.store.get_event(prev_event_id)
+                    ).content
+
+                membership = event_content.get("membership", Membership.LEAVE)
+                prev_membership = prev_event_content.get("membership", Membership.LEAVE)
+
+                if prev_membership == membership:
+                    continue
+
+                if prev_membership == Membership.JOIN:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "joined_members", -1
+                    )
+                elif prev_membership == Membership.INVITE:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "invited_members", -1
+                    )
+                elif prev_membership == Membership.LEAVE:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "left_members", -1
+                    )
+                elif prev_membership == Membership.BAN:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "banned_members", -1
+                    )
+                else:
+                    err = "%s is not a valid prev_membership" % (repr(prev_membership),)
+                    logger.error(err)
+                    raise ValueError(err)
+
+                if membership == Membership.JOIN:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "joined_members", +1
+                    )
+                elif membership == Membership.INVITE:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "invited_members", +1
+                    )
+                elif membership == Membership.LEAVE:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "left_members", +1
+                    )
+                elif membership == Membership.BAN:
+                    yield self.store.update_stats_delta(
+                        now, "room", room_id, "banned_members", +1
+                    )
+                else:
+                    err = "%s is not a valid membership" % (repr(membership),)
+                    logger.error(err)
+                    raise ValueError(err)
+
+                user_id = state_key
+                if self.is_mine_id(user_id):
+                    # update user_stats as it's one of our users
+                    public = yield self._is_public_room(room_id)
+
+                    if membership == Membership.LEAVE:
+                        yield self.store.update_stats_delta(
+                            now,
+                            "user",
+                            user_id,
+                            "public_rooms" if public else "private_rooms",
+                            -1,
+                        )
+                    elif membership == Membership.JOIN:
+                        yield self.store.update_stats_delta(
+                            now,
+                            "user",
+                            user_id,
+                            "public_rooms" if public else "private_rooms",
+                            +1,
+                        )
+
+            elif typ == EventTypes.Create:
+                # Newly created room. Add it with all blank portions.
+                yield self.store.update_room_state(
+                    room_id,
+                    {
+                        "join_rules": None,
+                        "history_visibility": None,
+                        "encryption": None,
+                        "name": None,
+                        "topic": None,
+                        "avatar": None,
+                        "canonical_alias": None,
+                    },
+                )
+
+            elif typ == EventTypes.JoinRules:
+                yield self.store.update_room_state(
+                    room_id, {"join_rules": event_content.get("join_rule")}
+                )
+
+                is_public = yield self._get_key_change(
+                    prev_event_id, event_id, "join_rule", JoinRules.PUBLIC
+                )
+                if is_public is not None:
+                    yield self.update_public_room_stats(now, room_id, is_public)
+
+            elif typ == EventTypes.RoomHistoryVisibility:
+                yield self.store.update_room_state(
+                    room_id,
+                    {"history_visibility": event_content.get("history_visibility")},
+                )
+
+                is_public = yield self._get_key_change(
+                    prev_event_id, event_id, "history_visibility", "world_readable"
+                )
+                if is_public is not None:
+                    yield self.update_public_room_stats(now, room_id, is_public)
+
+            elif typ == EventTypes.Encryption:
+                yield self.store.update_room_state(
+                    room_id, {"encryption": event_content.get("algorithm")}
+                )
+            elif typ == EventTypes.Name:
+                yield self.store.update_room_state(
+                    room_id, {"name": event_content.get("name")}
+                )
+            elif typ == EventTypes.Topic:
+                yield self.store.update_room_state(
+                    room_id, {"topic": event_content.get("topic")}
+                )
+            elif typ == EventTypes.RoomAvatar:
+                yield self.store.update_room_state(
+                    room_id, {"avatar": event_content.get("url")}
+                )
+            elif typ == EventTypes.CanonicalAlias:
+                yield self.store.update_room_state(
+                    room_id, {"canonical_alias": event_content.get("alias")}
+                )
+
+    @defer.inlineCallbacks
+    def update_public_room_stats(self, ts, room_id, is_public):
+        """
+        Increment/decrement a user's number of public rooms when a room they are
+        in changes to/from public visibility.
+
+        Args:
+            ts (int): Timestamp in seconds
+            room_id (str)
+            is_public (bool)
+        """
+        # For now, blindly iterate over all local users in the room so that
+        # we can handle the whole problem of copying buckets over as needed
+        user_ids = yield self.store.get_users_in_room(room_id)
+
+        for user_id in user_ids:
+            if self.hs.is_mine(UserID.from_string(user_id)):
+                yield self.store.update_stats_delta(
+                    ts, "user", user_id, "public_rooms", +1 if is_public else -1
+                )
+                yield self.store.update_stats_delta(
+                    ts, "user", user_id, "private_rooms", -1 if is_public else +1
+                )
+
+    @defer.inlineCallbacks
+    def _is_public_room(self, room_id):
+        join_rules = yield self.state.get_current_state(room_id, EventTypes.JoinRules)
+        history_visibility = yield self.state.get_current_state(
+            room_id, EventTypes.RoomHistoryVisibility
+        )
+
+        if (join_rules and join_rules.content.get("join_rule") == JoinRules.PUBLIC) or (
+            (
+                history_visibility
+                and history_visibility.content.get("history_visibility")
+                == "world_readable"
+            )
+        ):
+            defer.returnValue(True)
+        else:
+            defer.returnValue(False)
diff --git a/synapse/http/servlet.py b/synapse/http/servlet.py
index 528125e737..197c652850 100644
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@@ -55,7 +55,7 @@ def parse_integer_from_args(args, name, default=None, required=False):
             return int(args[name][0])
         except Exception:
             message = "Query parameter %r must be an integer" % (name,)
-            raise SynapseError(400, message)
+            raise SynapseError(400, message, errcode=Codes.INVALID_PARAM)
     else:
         if required:
             message = "Missing integer query parameter %r" % (name,)
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 2708f5e820..f64baa4d58 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -16,7 +16,12 @@
 
 import logging
 
-from pkg_resources import DistributionNotFound, VersionConflict, get_distribution
+from pkg_resources import (
+    DistributionNotFound,
+    Requirement,
+    VersionConflict,
+    get_provider,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -53,7 +58,7 @@ REQUIREMENTS = [
     "pyasn1-modules>=0.0.7",
     "daemonize>=2.3.1",
     "bcrypt>=3.1.0",
-    "pillow>=3.1.2",
+    "pillow>=4.3.0",
     "sortedcontainers>=1.4.4",
     "psutil>=2.0.0",
     "pymacaroons>=0.13.0",
@@ -69,14 +74,6 @@ REQUIREMENTS = [
     "attrs>=17.4.0",
 
     "netaddr>=0.7.18",
-
-    # requests is a transitive dep of treq, and urlib3 is a transitive dep
-    # of requests, as well as of sentry-sdk.
-    #
-    # As of requests 2.21, requests does not yet support urllib3 1.25.
-    # (If we do not pin it here, pip will give us the latest urllib3
-    # due to the dep via sentry-sdk.)
-    "urllib3<1.25",
 ]
 
 CONDITIONAL_REQUIREMENTS = {
@@ -91,7 +88,13 @@ CONDITIONAL_REQUIREMENTS = {
 
     # ACME support is required to provision TLS certificates from authorities
     # that use the protocol, such as Let's Encrypt.
-    "acme": ["txacme>=0.9.2"],
+    "acme": [
+        "txacme>=0.9.2",
+
+        # txacme depends on eliot. Eliot 1.8.0 is incompatible with
+        # python 3.5.2, as per https://github.com/itamarst/eliot/issues/418
+        'eliot<1.8.0;python_version<"3.5.3"',
+    ],
 
     "saml2": ["pysaml2>=4.5.0"],
     "systemd": ["systemd-python>=231"],
@@ -125,10 +128,10 @@ class DependencyException(Exception):
     @property
     def dependencies(self):
         for i in self.args[0]:
-            yield '"' + i + '"'
+            yield "'" + i + "'"
 
 
-def check_requirements(for_feature=None, _get_distribution=get_distribution):
+def check_requirements(for_feature=None):
     deps_needed = []
     errors = []
 
@@ -139,7 +142,7 @@ def check_requirements(for_feature=None, _get_distribution=get_distribution):
 
     for dependency in reqs:
         try:
-            _get_distribution(dependency)
+            _check_requirement(dependency)
         except VersionConflict as e:
             deps_needed.append(dependency)
             errors.append(
@@ -157,7 +160,7 @@ def check_requirements(for_feature=None, _get_distribution=get_distribution):
 
         for dependency in OPTS:
             try:
-                _get_distribution(dependency)
+                _check_requirement(dependency)
             except VersionConflict as e:
                 deps_needed.append(dependency)
                 errors.append(
@@ -175,6 +178,23 @@ def check_requirements(for_feature=None, _get_distribution=get_distribution):
         raise DependencyException(deps_needed)
 
 
+def _check_requirement(dependency_string):
+    """Parses a dependency string, and checks if the specified requirement is installed
+
+    Raises:
+        VersionConflict if the requirement is installed, but with the the wrong version
+        DistributionNotFound if nothing is found to provide the requirement
+    """
+    req = Requirement.parse(dependency_string)
+
+    # first check if the markers specify that this requirement needs installing
+    if req.marker is not None and not req.marker.evaluate():
+        # not required for this environment
+        return
+
+    get_provider(req)
+
+
 if __name__ == "__main__":
     import sys
 
diff --git a/synapse/replication/slave/storage/events.py b/synapse/replication/slave/storage/events.py
index b457c5563f..a3952506c1 100644
--- a/synapse/replication/slave/storage/events.py
+++ b/synapse/replication/slave/storage/events.py
@@ -23,6 +23,7 @@ from synapse.replication.tcp.streams.events import (
 from synapse.storage.event_federation import EventFederationWorkerStore
 from synapse.storage.event_push_actions import EventPushActionsWorkerStore
 from synapse.storage.events_worker import EventsWorkerStore
+from synapse.storage.relations import RelationsWorkerStore
 from synapse.storage.roommember import RoomMemberWorkerStore
 from synapse.storage.signatures import SignatureWorkerStore
 from synapse.storage.state import StateGroupWorkerStore
@@ -52,6 +53,7 @@ class SlavedEventStore(EventFederationWorkerStore,
                        EventsWorkerStore,
                        SignatureWorkerStore,
                        UserErasureWorkerStore,
+                       RelationsWorkerStore,
                        BaseSlavedStore):
 
     def __init__(self, db_conn, hs):
@@ -89,7 +91,7 @@ class SlavedEventStore(EventFederationWorkerStore,
             for row in rows:
                 self.invalidate_caches_for_event(
                     -token, row.event_id, row.room_id, row.type, row.state_key,
-                    row.redacts,
+                    row.redacts, row.relates_to,
                     backfilled=True,
                 )
         return super(SlavedEventStore, self).process_replication_rows(
@@ -102,7 +104,7 @@ class SlavedEventStore(EventFederationWorkerStore,
         if row.type == EventsStreamEventRow.TypeId:
             self.invalidate_caches_for_event(
                 token, data.event_id, data.room_id, data.type, data.state_key,
-                data.redacts,
+                data.redacts, data.relates_to,
                 backfilled=False,
             )
         elif row.type == EventsStreamCurrentStateRow.TypeId:
@@ -114,7 +116,8 @@ class SlavedEventStore(EventFederationWorkerStore,
             raise Exception("Unknown events stream row type %s" % (row.type, ))
 
     def invalidate_caches_for_event(self, stream_ordering, event_id, room_id,
-                                    etype, state_key, redacts, backfilled):
+                                    etype, state_key, redacts, relates_to,
+                                    backfilled):
         self._invalidate_get_event_cache(event_id)
 
         self.get_latest_event_ids_in_room.invalidate((room_id,))
@@ -136,3 +139,8 @@ class SlavedEventStore(EventFederationWorkerStore,
                 state_key, stream_ordering
             )
             self.get_invited_rooms_for_user.invalidate((state_key,))
+
+        if relates_to:
+            self.get_relations_for_event.invalidate_many((relates_to,))
+            self.get_aggregation_groups_for_event.invalidate_many((relates_to,))
+            self.get_applicable_edit.invalidate((relates_to,))
diff --git a/synapse/replication/tcp/streams/_base.py b/synapse/replication/tcp/streams/_base.py
index 8971a6a22e..b6ce7a7bee 100644
--- a/synapse/replication/tcp/streams/_base.py
+++ b/synapse/replication/tcp/streams/_base.py
@@ -32,6 +32,7 @@ BackfillStreamRow = namedtuple("BackfillStreamRow", (
     "type",  # str
     "state_key",  # str, optional
     "redacts",  # str, optional
+    "relates_to",  # str, optional
 ))
 PresenceStreamRow = namedtuple("PresenceStreamRow", (
     "user_id",  # str
diff --git a/synapse/replication/tcp/streams/events.py b/synapse/replication/tcp/streams/events.py
index e0f6e29248..f1290d022a 100644
--- a/synapse/replication/tcp/streams/events.py
+++ b/synapse/replication/tcp/streams/events.py
@@ -80,11 +80,12 @@ class BaseEventsStreamRow(object):
 class EventsStreamEventRow(BaseEventsStreamRow):
     TypeId = "ev"
 
-    event_id = attr.ib()   # str
-    room_id = attr.ib()    # str
-    type = attr.ib()       # str
-    state_key = attr.ib()  # str, optional
-    redacts = attr.ib()    # str, optional
+    event_id = attr.ib()    # str
+    room_id = attr.ib()     # str
+    type = attr.ib()        # str
+    state_key = attr.ib()   # str, optional
+    redacts = attr.ib()     # str, optional
+    relates_to = attr.ib()  # str, optional
 
 
 @attr.s(slots=True, frozen=True)
diff --git a/synapse/rest/__init__.py b/synapse/rest/__init__.py
index 3a24d31d1b..e6110ad9b1 100644
--- a/synapse/rest/__init__.py
+++ b/synapse/rest/__init__.py
@@ -44,6 +44,7 @@ from synapse.rest.client.v2_alpha import (
     read_marker,
     receipts,
     register,
+    relations,
     report_event,
     room_keys,
     room_upgrade_rest_servlet,
@@ -115,6 +116,7 @@ class ClientRestResource(JsonResource):
         room_upgrade_rest_servlet.register_servlets(hs, client_resource)
         capabilities.register_servlets(hs, client_resource)
         account_validity.register_servlets(hs, client_resource)
+        relations.register_servlets(hs, client_resource)
 
         # moving to /_synapse/admin
         synapse.rest.admin.register_servlets_for_client_rest_resource(
diff --git a/synapse/rest/client/v2_alpha/capabilities.py b/synapse/rest/client/v2_alpha/capabilities.py
index a868d06098..2b4892330c 100644
--- a/synapse/rest/client/v2_alpha/capabilities.py
+++ b/synapse/rest/client/v2_alpha/capabilities.py
@@ -16,7 +16,7 @@ import logging
 
 from twisted.internet import defer
 
-from synapse.api.room_versions import DEFAULT_ROOM_VERSION, KNOWN_ROOM_VERSIONS
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.http.servlet import RestServlet
 
 from ._base import client_v2_patterns
@@ -36,6 +36,7 @@ class CapabilitiesRestServlet(RestServlet):
         """
         super(CapabilitiesRestServlet, self).__init__()
         self.hs = hs
+        self.config = hs.config
         self.auth = hs.get_auth()
         self.store = hs.get_datastore()
 
@@ -48,7 +49,7 @@ class CapabilitiesRestServlet(RestServlet):
         response = {
             "capabilities": {
                 "m.room_versions": {
-                    "default": DEFAULT_ROOM_VERSION.identifier,
+                    "default": self.config.default_room_version.identifier,
                     "available": {
                         v.identifier: v.disposition
                         for v in KNOWN_ROOM_VERSIONS.values()
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index fa0cedb8d4..042f636135 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -348,18 +348,22 @@ class RegisterRestServlet(RestServlet):
         if self.hs.config.enable_registration_captcha:
             # only support 3PIDless registration if no 3PIDs are required
             if not require_email and not require_msisdn:
-                flows.extend([[LoginType.RECAPTCHA]])
+                # Also add a dummy flow here, otherwise if a client completes
+                # recaptcha first we'll assume they were going for this flow
+                # and complete the request, when they could have been trying to
+                # complete one of the flows with email/msisdn auth.
+                flows.extend([[LoginType.RECAPTCHA, LoginType.DUMMY]])
             # only support the email-only flow if we don't require MSISDN 3PIDs
             if not require_msisdn:
-                flows.extend([[LoginType.EMAIL_IDENTITY, LoginType.RECAPTCHA]])
+                flows.extend([[LoginType.RECAPTCHA, LoginType.EMAIL_IDENTITY]])
 
             if show_msisdn:
                 # only support the MSISDN-only flow if we don't require email 3PIDs
                 if not require_email:
-                    flows.extend([[LoginType.MSISDN, LoginType.RECAPTCHA]])
+                    flows.extend([[LoginType.RECAPTCHA, LoginType.MSISDN]])
                 # always let users provide both MSISDN & email
                 flows.extend([
-                    [LoginType.MSISDN, LoginType.EMAIL_IDENTITY, LoginType.RECAPTCHA],
+                    [LoginType.RECAPTCHA, LoginType.MSISDN, LoginType.EMAIL_IDENTITY],
                 ])
         else:
             # only support 3PIDless registration if no 3PIDs are required
@@ -382,7 +386,15 @@ class RegisterRestServlet(RestServlet):
         if self.hs.config.user_consent_at_registration:
             new_flows = []
             for flow in flows:
-                flow.append(LoginType.TERMS)
+                inserted = False
+                # m.login.terms should go near the end but before msisdn or email auth
+                for i, stage in enumerate(flow):
+                    if stage == LoginType.EMAIL_IDENTITY or stage == LoginType.MSISDN:
+                        flow.insert(i, LoginType.TERMS)
+                        inserted = True
+                        break
+                if not inserted:
+                    flow.append(LoginType.TERMS)
             flows.extend(new_flows)
 
         auth_result, params, session_id = yield self.auth_handler.check_auth(
diff --git a/synapse/rest/client/v2_alpha/relations.py b/synapse/rest/client/v2_alpha/relations.py
new file mode 100644
index 0000000000..41e0a44936
--- /dev/null
+++ b/synapse/rest/client/v2_alpha/relations.py
@@ -0,0 +1,338 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""This class implements the proposed relation APIs from MSC 1849.
+
+Since the MSC has not been approved all APIs here are unstable and may change at
+any time to reflect changes in the MSC.
+"""
+
+import logging
+
+from twisted.internet import defer
+
+from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.errors import SynapseError
+from synapse.http.servlet import (
+    RestServlet,
+    parse_integer,
+    parse_json_object_from_request,
+    parse_string,
+)
+from synapse.rest.client.transactions import HttpTransactionCache
+from synapse.storage.relations import AggregationPaginationToken, RelationPaginationToken
+
+from ._base import client_v2_patterns
+
+logger = logging.getLogger(__name__)
+
+
+class RelationSendServlet(RestServlet):
+    """Helper API for sending events that have relation data.
+
+    Example API shape to send a 👍 reaction to a room:
+
+        POST /rooms/!foo/send_relation/$bar/m.annotation/m.reaction?key=%F0%9F%91%8D
+        {}
+
+        {
+            "event_id": "$foobar"
+        }
+    """
+
+    PATTERN = (
+        "/rooms/(?P<room_id>[^/]*)/send_relation"
+        "/(?P<parent_id>[^/]*)/(?P<relation_type>[^/]*)/(?P<event_type>[^/]*)"
+    )
+
+    def __init__(self, hs):
+        super(RelationSendServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.event_creation_handler = hs.get_event_creation_handler()
+        self.txns = HttpTransactionCache(hs)
+
+    def register(self, http_server):
+        http_server.register_paths(
+            "POST",
+            client_v2_patterns(self.PATTERN + "$", releases=()),
+            self.on_PUT_or_POST,
+        )
+        http_server.register_paths(
+            "PUT",
+            client_v2_patterns(self.PATTERN + "/(?P<txn_id>[^/]*)$", releases=()),
+            self.on_PUT,
+        )
+
+    def on_PUT(self, request, *args, **kwargs):
+        return self.txns.fetch_or_execute_request(
+            request, self.on_PUT_or_POST, request, *args, **kwargs
+        )
+
+    @defer.inlineCallbacks
+    def on_PUT_or_POST(
+        self, request, room_id, parent_id, relation_type, event_type, txn_id=None
+    ):
+        requester = yield self.auth.get_user_by_req(request, allow_guest=True)
+
+        if event_type == EventTypes.Member:
+            # Add relations to a membership is meaningless, so we just deny it
+            # at the CS API rather than trying to handle it correctly.
+            raise SynapseError(400, "Cannot send member events with relations")
+
+        content = parse_json_object_from_request(request)
+
+        aggregation_key = parse_string(request, "key", encoding="utf-8")
+
+        content["m.relates_to"] = {
+            "event_id": parent_id,
+            "key": aggregation_key,
+            "rel_type": relation_type,
+        }
+
+        event_dict = {
+            "type": event_type,
+            "content": content,
+            "room_id": room_id,
+            "sender": requester.user.to_string(),
+        }
+
+        event = yield self.event_creation_handler.create_and_send_nonmember_event(
+            requester, event_dict=event_dict, txn_id=txn_id
+        )
+
+        defer.returnValue((200, {"event_id": event.event_id}))
+
+
+class RelationPaginationServlet(RestServlet):
+    """API to paginate relations on an event by topological ordering, optionally
+    filtered by relation type and event type.
+    """
+
+    PATTERNS = client_v2_patterns(
+        "/rooms/(?P<room_id>[^/]*)/relations/(?P<parent_id>[^/]*)"
+        "(/(?P<relation_type>[^/]*)(/(?P<event_type>[^/]*))?)?$",
+        releases=(),
+    )
+
+    def __init__(self, hs):
+        super(RelationPaginationServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastore()
+        self.clock = hs.get_clock()
+        self._event_serializer = hs.get_event_client_serializer()
+        self.event_handler = hs.get_event_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, room_id, parent_id, relation_type=None, event_type=None):
+        requester = yield self.auth.get_user_by_req(request, allow_guest=True)
+
+        yield self.auth.check_in_room_or_world_readable(
+            room_id, requester.user.to_string()
+        )
+
+        # This checks that a) the event exists and b) the user is allowed to
+        # view it.
+        yield self.event_handler.get_event(requester.user, room_id, parent_id)
+
+        limit = parse_integer(request, "limit", default=5)
+        from_token = parse_string(request, "from")
+        to_token = parse_string(request, "to")
+
+        if from_token:
+            from_token = RelationPaginationToken.from_string(from_token)
+
+        if to_token:
+            to_token = RelationPaginationToken.from_string(to_token)
+
+        result = yield self.store.get_relations_for_event(
+            event_id=parent_id,
+            relation_type=relation_type,
+            event_type=event_type,
+            limit=limit,
+            from_token=from_token,
+            to_token=to_token,
+        )
+
+        events = yield self.store.get_events_as_list(
+            [c["event_id"] for c in result.chunk]
+        )
+
+        now = self.clock.time_msec()
+        events = yield self._event_serializer.serialize_events(events, now)
+
+        return_value = result.to_dict()
+        return_value["chunk"] = events
+
+        defer.returnValue((200, return_value))
+
+
+class RelationAggregationPaginationServlet(RestServlet):
+    """API to paginate aggregation groups of relations, e.g. paginate the
+    types and counts of the reactions on the events.
+
+    Example request and response:
+
+        GET /rooms/{room_id}/aggregations/{parent_id}
+
+        {
+            chunk: [
+                {
+                    "type": "m.reaction",
+                    "key": "👍",
+                    "count": 3
+                }
+            ]
+        }
+    """
+
+    PATTERNS = client_v2_patterns(
+        "/rooms/(?P<room_id>[^/]*)/aggregations/(?P<parent_id>[^/]*)"
+        "(/(?P<relation_type>[^/]*)(/(?P<event_type>[^/]*))?)?$",
+        releases=(),
+    )
+
+    def __init__(self, hs):
+        super(RelationAggregationPaginationServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastore()
+        self.event_handler = hs.get_event_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, room_id, parent_id, relation_type=None, event_type=None):
+        requester = yield self.auth.get_user_by_req(request, allow_guest=True)
+
+        yield self.auth.check_in_room_or_world_readable(
+            room_id, requester.user.to_string()
+        )
+
+        # This checks that a) the event exists and b) the user is allowed to
+        # view it.
+        yield self.event_handler.get_event(requester.user, room_id, parent_id)
+
+        if relation_type not in (RelationTypes.ANNOTATION, None):
+            raise SynapseError(400, "Relation type must be 'annotation'")
+
+        limit = parse_integer(request, "limit", default=5)
+        from_token = parse_string(request, "from")
+        to_token = parse_string(request, "to")
+
+        if from_token:
+            from_token = AggregationPaginationToken.from_string(from_token)
+
+        if to_token:
+            to_token = AggregationPaginationToken.from_string(to_token)
+
+        res = yield self.store.get_aggregation_groups_for_event(
+            event_id=parent_id,
+            event_type=event_type,
+            limit=limit,
+            from_token=from_token,
+            to_token=to_token,
+        )
+
+        defer.returnValue((200, res.to_dict()))
+
+
+class RelationAggregationGroupPaginationServlet(RestServlet):
+    """API to paginate within an aggregation group of relations, e.g. paginate
+    all the 👍 reactions on an event.
+
+    Example request and response:
+
+        GET /rooms/{room_id}/aggregations/{parent_id}/m.annotation/m.reaction/👍
+
+        {
+            chunk: [
+                {
+                    "type": "m.reaction",
+                    "content": {
+                        "m.relates_to": {
+                            "rel_type": "m.annotation",
+                            "key": "👍"
+                        }
+                    }
+                },
+                ...
+            ]
+        }
+    """
+
+    PATTERNS = client_v2_patterns(
+        "/rooms/(?P<room_id>[^/]*)/aggregations/(?P<parent_id>[^/]*)"
+        "/(?P<relation_type>[^/]*)/(?P<event_type>[^/]*)/(?P<key>[^/]*)$",
+        releases=(),
+    )
+
+    def __init__(self, hs):
+        super(RelationAggregationGroupPaginationServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastore()
+        self.clock = hs.get_clock()
+        self._event_serializer = hs.get_event_client_serializer()
+        self.event_handler = hs.get_event_handler()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, room_id, parent_id, relation_type, event_type, key):
+        requester = yield self.auth.get_user_by_req(request, allow_guest=True)
+
+        yield self.auth.check_in_room_or_world_readable(
+            room_id, requester.user.to_string()
+        )
+
+        # This checks that a) the event exists and b) the user is allowed to
+        # view it.
+        yield self.event_handler.get_event(requester.user, room_id, parent_id)
+
+        if relation_type != RelationTypes.ANNOTATION:
+            raise SynapseError(400, "Relation type must be 'annotation'")
+
+        limit = parse_integer(request, "limit", default=5)
+        from_token = parse_string(request, "from")
+        to_token = parse_string(request, "to")
+
+        if from_token:
+            from_token = RelationPaginationToken.from_string(from_token)
+
+        if to_token:
+            to_token = RelationPaginationToken.from_string(to_token)
+
+        result = yield self.store.get_relations_for_event(
+            event_id=parent_id,
+            relation_type=relation_type,
+            event_type=event_type,
+            aggregation_key=key,
+            limit=limit,
+            from_token=from_token,
+            to_token=to_token,
+        )
+
+        events = yield self.store.get_events_as_list(
+            [c["event_id"] for c in result.chunk]
+        )
+
+        now = self.clock.time_msec()
+        events = yield self._event_serializer.serialize_events(events, now)
+
+        return_value = result.to_dict()
+        return_value["chunk"] = events
+
+        defer.returnValue((200, return_value))
+
+
+def register_servlets(hs, http_server):
+    RelationSendServlet(hs).register(http_server)
+    RelationPaginationServlet(hs).register(http_server)
+    RelationAggregationPaginationServlet(hs).register(http_server)
+    RelationAggregationGroupPaginationServlet(hs).register(http_server)
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index c701e534e7..d3025025e3 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -358,6 +358,9 @@ class SyncRestServlet(RestServlet):
         def serialize(events):
             return self._event_serializer.serialize_events(
                 events, time_now=time_now,
+                # We don't bundle "live" events, as otherwise clients
+                # will end up double counting annotations.
+                bundle_aggregations=False,
                 token_id=token_id,
                 event_format=event_formatter,
                 only_event_fields=only_fields,
diff --git a/synapse/rest/key/v2/remote_key_resource.py b/synapse/rest/key/v2/remote_key_resource.py
index eb8782aa6e..21c3c807b9 100644
--- a/synapse/rest/key/v2/remote_key_resource.py
+++ b/synapse/rest/key/v2/remote_key_resource.py
@@ -20,7 +20,7 @@ from twisted.web.resource import Resource
 from twisted.web.server import NOT_DONE_YET
 
 from synapse.api.errors import Codes, SynapseError
-from synapse.crypto.keyring import KeyLookupError
+from synapse.crypto.keyring import KeyLookupError, ServerKeyFetcher
 from synapse.http.server import respond_with_json_bytes, wrap_json_request_handler
 from synapse.http.servlet import parse_integer, parse_json_object_from_request
 
@@ -89,7 +89,7 @@ class RemoteKey(Resource):
     isLeaf = True
 
     def __init__(self, hs):
-        self.keyring = hs.get_keyring()
+        self.fetcher = ServerKeyFetcher(hs)
         self.store = hs.get_datastore()
         self.clock = hs.get_clock()
         self.federation_domain_whitelist = hs.config.federation_domain_whitelist
@@ -217,7 +217,7 @@ class RemoteKey(Resource):
         if cache_misses and query_remote_on_cache_miss:
             for server_name, key_ids in cache_misses.items():
                 try:
-                    yield self.keyring.get_server_verify_key_v2_direct(
+                    yield self.fetcher.get_server_verify_key_v2_direct(
                         server_name, key_ids
                     )
                 except KeyLookupError as e:
diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index bdffa97805..8569677355 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -444,6 +444,9 @@ class MediaRepository(object):
             )
             return
 
+        if thumbnailer.transpose_method is not None:
+            m_width, m_height = thumbnailer.transpose()
+
         if t_method == "crop":
             t_byte_source = thumbnailer.crop(t_width, t_height, t_type)
         elif t_method == "scale":
@@ -578,6 +581,12 @@ class MediaRepository(object):
             )
             return
 
+        if thumbnailer.transpose_method is not None:
+            m_width, m_height = yield logcontext.defer_to_thread(
+                self.hs.get_reactor(),
+                thumbnailer.transpose
+            )
+
         # We deduplicate the thumbnail sizes by ignoring the cropped versions if
         # they have the same dimensions of a scaled one.
         thumbnails = {}
diff --git a/synapse/rest/media/v1/thumbnailer.py b/synapse/rest/media/v1/thumbnailer.py
index a4b26c2587..3efd0d80fc 100644
--- a/synapse/rest/media/v1/thumbnailer.py
+++ b/synapse/rest/media/v1/thumbnailer.py
@@ -20,6 +20,17 @@ import PIL.Image as Image
 
 logger = logging.getLogger(__name__)
 
+EXIF_ORIENTATION_TAG = 0x0112
+EXIF_TRANSPOSE_MAPPINGS = {
+    2: Image.FLIP_LEFT_RIGHT,
+    3: Image.ROTATE_180,
+    4: Image.FLIP_TOP_BOTTOM,
+    5: Image.TRANSPOSE,
+    6: Image.ROTATE_270,
+    7: Image.TRANSVERSE,
+    8: Image.ROTATE_90
+}
+
 
 class Thumbnailer(object):
 
@@ -31,6 +42,30 @@ class Thumbnailer(object):
     def __init__(self, input_path):
         self.image = Image.open(input_path)
         self.width, self.height = self.image.size
+        self.transpose_method = None
+        try:
+            # We don't use ImageOps.exif_transpose since it crashes with big EXIF
+            image_exif = self.image._getexif()
+            if image_exif is not None:
+                image_orientation = image_exif.get(EXIF_ORIENTATION_TAG)
+                self.transpose_method = EXIF_TRANSPOSE_MAPPINGS.get(image_orientation)
+        except Exception as e:
+            # A lot of parsing errors can happen when parsing EXIF
+            logger.info("Error parsing image EXIF information: %s", e)
+
+    def transpose(self):
+        """Transpose the image using its EXIF Orientation tag
+
+        Returns:
+            Tuple[int, int]: (width, height) containing the new image size in pixels.
+        """
+        if self.transpose_method is not None:
+            self.image = self.image.transpose(self.transpose_method)
+            self.width, self.height = self.image.size
+            self.transpose_method = None
+            # We don't need EXIF any more
+            self.image.info["exif"] = None
+        return self.image.size
 
     def aspect(self, max_width, max_height):
         """Calculate the largest size that preserves aspect ratio which
diff --git a/synapse/server.py b/synapse/server.py
index 80d40b9272..9229a68a8d 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -72,6 +72,7 @@ from synapse.handlers.room_list import RoomListHandler
 from synapse.handlers.room_member import RoomMemberMasterHandler
 from synapse.handlers.room_member_worker import RoomMemberWorkerHandler
 from synapse.handlers.set_password import SetPasswordHandler
+from synapse.handlers.stats import StatsHandler
 from synapse.handlers.sync import SyncHandler
 from synapse.handlers.typing import TypingHandler
 from synapse.handlers.user_directory import UserDirectoryHandler
@@ -139,6 +140,7 @@ class HomeServer(object):
         'acme_handler',
         'auth_handler',
         'device_handler',
+        'stats_handler',
         'e2e_keys_handler',
         'e2e_room_keys_handler',
         'event_handler',
@@ -191,6 +193,7 @@ class HomeServer(object):
 
     REQUIRED_ON_MASTER_STARTUP = [
         "user_directory_handler",
+        "stats_handler"
     ]
 
     # This is overridden in derived application classes
@@ -474,6 +477,9 @@ class HomeServer(object):
     def build_secrets(self):
         return Secrets()
 
+    def build_stats_handler(self):
+        return StatsHandler(self)
+
     def build_spam_checker(self):
         return SpamChecker(self)
 
diff --git a/synapse/storage/__init__.py b/synapse/storage/__init__.py
index c432041b4e..66675d08ae 100644
--- a/synapse/storage/__init__.py
+++ b/synapse/storage/__init__.py
@@ -49,11 +49,13 @@ from .pusher import PusherStore
 from .receipts import ReceiptsStore
 from .registration import RegistrationStore
 from .rejections import RejectionsStore
+from .relations import RelationsStore
 from .room import RoomStore
 from .roommember import RoomMemberStore
 from .search import SearchStore
 from .signatures import SignatureStore
 from .state import StateStore
+from .stats import StatsStore
 from .stream import StreamStore
 from .tags import TagsStore
 from .transactions import TransactionStore
@@ -99,6 +101,8 @@ class DataStore(
     GroupServerStore,
     UserErasureStore,
     MonthlyActiveUsersStore,
+    StatsStore,
+    RelationsStore,
 ):
     def __init__(self, db_conn, hs):
         self.hs = hs
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 7a7f841c6c..2ffc27ff41 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -575,10 +575,11 @@ class EventsStore(
 
         def _get_events(txn, batch):
             sql = """
-            SELECT prev_event_id
+            SELECT prev_event_id, internal_metadata
             FROM event_edges
                 INNER JOIN events USING (event_id)
                 LEFT JOIN rejections USING (event_id)
+                LEFT JOIN event_json USING (event_id)
             WHERE
                 prev_event_id IN (%s)
                 AND NOT events.outlier
@@ -588,7 +589,11 @@ class EventsStore(
             )
 
             txn.execute(sql, batch)
-            results.extend(r[0] for r in txn)
+            results.extend(
+                r[0]
+                for r in txn
+                if not json.loads(r[1]).get("soft_failed")
+            )
 
         for chunk in batch_iter(event_ids, 100):
             yield self.runInteraction("_get_events_which_are_prevs", _get_events, chunk)
@@ -1325,6 +1330,9 @@ class EventsStore(
                     txn, event.room_id, event.redacts
                 )
 
+                # Remove from relations table.
+                self._handle_redaction(txn, event.redacts)
+
         # Update the event_forward_extremities, event_backward_extremities and
         # event_edges tables.
         self._handle_mult_prev_events(
@@ -1351,6 +1359,8 @@ class EventsStore(
                 # Insert into the event_search table.
                 self._store_guest_access_txn(txn, event)
 
+            self._handle_event_relations(txn, event)
+
         # Insert into the room_memberships table.
         self._store_room_members_txn(
             txn,
@@ -1655,10 +1665,11 @@ class EventsStore(
         def get_all_new_forward_event_rows(txn):
             sql = (
                 "SELECT e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
+                " state_key, redacts, relates_to_id"
                 " FROM events AS e"
                 " LEFT JOIN redactions USING (event_id)"
                 " LEFT JOIN state_events USING (event_id)"
+                " LEFT JOIN event_relations USING (event_id)"
                 " WHERE ? < stream_ordering AND stream_ordering <= ?"
                 " ORDER BY stream_ordering ASC"
                 " LIMIT ?"
@@ -1673,11 +1684,12 @@ class EventsStore(
 
             sql = (
                 "SELECT event_stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
+                " state_key, redacts, relates_to_id"
                 " FROM events AS e"
                 " INNER JOIN ex_outlier_stream USING (event_id)"
                 " LEFT JOIN redactions USING (event_id)"
                 " LEFT JOIN state_events USING (event_id)"
+                " LEFT JOIN event_relations USING (event_id)"
                 " WHERE ? < event_stream_ordering"
                 " AND event_stream_ordering <= ?"
                 " ORDER BY event_stream_ordering DESC"
@@ -1698,10 +1710,11 @@ class EventsStore(
         def get_all_new_backfill_event_rows(txn):
             sql = (
                 "SELECT -e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
+                " state_key, redacts, relates_to_id"
                 " FROM events AS e"
                 " LEFT JOIN redactions USING (event_id)"
                 " LEFT JOIN state_events USING (event_id)"
+                " LEFT JOIN event_relations USING (event_id)"
                 " WHERE ? > stream_ordering AND stream_ordering >= ?"
                 " ORDER BY stream_ordering ASC"
                 " LIMIT ?"
@@ -1716,11 +1729,12 @@ class EventsStore(
 
             sql = (
                 "SELECT -event_stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
+                " state_key, redacts, relates_to_id"
                 " FROM events AS e"
                 " INNER JOIN ex_outlier_stream USING (event_id)"
                 " LEFT JOIN redactions USING (event_id)"
                 " LEFT JOIN state_events USING (event_id)"
+                " LEFT JOIN event_relations USING (event_id)"
                 " WHERE ? > event_stream_ordering"
                 " AND event_stream_ordering >= ?"
                 " ORDER BY event_stream_ordering DESC"
diff --git a/synapse/storage/events_worker.py b/synapse/storage/events_worker.py
index adc6cf26b5..21b353cad3 100644
--- a/synapse/storage/events_worker.py
+++ b/synapse/storage/events_worker.py
@@ -610,4 +610,28 @@ class EventsWorkerStore(SQLBaseStore):
 
             return res
 
-        return self.runInteraction("get_rejection_reasons", f)
+        return self.runInteraction("get_seen_events_with_rejections", f)
+
+    def _get_total_state_event_counts_txn(self, txn, room_id):
+        """
+        See get_state_event_counts.
+        """
+        sql = "SELECT COUNT(*) FROM state_events WHERE room_id=?"
+        txn.execute(sql, (room_id,))
+        row = txn.fetchone()
+        return row[0] if row else 0
+
+    def get_total_state_event_counts(self, room_id):
+        """
+        Gets the total number of state events in a room.
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[int]
+        """
+        return self.runInteraction(
+            "get_total_state_event_counts",
+            self._get_total_state_event_counts_txn, room_id
+        )
diff --git a/synapse/storage/keys.py b/synapse/storage/keys.py
index 7036541792..5300720dbb 100644
--- a/synapse/storage/keys.py
+++ b/synapse/storage/keys.py
@@ -19,6 +19,7 @@ import logging
 
 import six
 
+import attr
 from signedjson.key import decode_verify_key_bytes
 
 from synapse.util import batch_iter
@@ -36,6 +37,12 @@ else:
     db_binary_type = memoryview
 
 
+@attr.s(slots=True, frozen=True)
+class FetchKeyResult(object):
+    verify_key = attr.ib()  # VerifyKey: the key itself
+    valid_until_ts = attr.ib()  # int: how long we can use this key for
+
+
 class KeyStore(SQLBaseStore):
     """Persistence for signature verification keys
     """
@@ -54,8 +61,8 @@ class KeyStore(SQLBaseStore):
                 iterable of (server_name, key-id) tuples to fetch keys for
 
         Returns:
-            Deferred: resolves to dict[Tuple[str, str], VerifyKey|None]:
-                map from (server_name, key_id) -> VerifyKey, or None if the key is
+            Deferred: resolves to dict[Tuple[str, str], FetchKeyResult|None]:
+                map from (server_name, key_id) -> FetchKeyResult, or None if the key is
                 unknown
         """
         keys = {}
@@ -65,17 +72,19 @@ class KeyStore(SQLBaseStore):
 
             # batch_iter always returns tuples so it's safe to do len(batch)
             sql = (
-                "SELECT server_name, key_id, verify_key FROM server_signature_keys "
-                "WHERE 1=0"
+                "SELECT server_name, key_id, verify_key, ts_valid_until_ms "
+                "FROM server_signature_keys WHERE 1=0"
             ) + " OR (server_name=? AND key_id=?)" * len(batch)
 
             txn.execute(sql, tuple(itertools.chain.from_iterable(batch)))
 
             for row in txn:
-                server_name, key_id, key_bytes = row
-                keys[(server_name, key_id)] = decode_verify_key_bytes(
-                    key_id, bytes(key_bytes)
+                server_name, key_id, key_bytes, ts_valid_until_ms = row
+                res = FetchKeyResult(
+                    verify_key=decode_verify_key_bytes(key_id, bytes(key_bytes)),
+                    valid_until_ts=ts_valid_until_ms,
                 )
+                keys[(server_name, key_id)] = res
 
         def _txn(txn):
             for batch in batch_iter(server_name_and_key_ids, 50):
@@ -84,38 +93,53 @@ class KeyStore(SQLBaseStore):
 
         return self.runInteraction("get_server_verify_keys", _txn)
 
-    def store_server_verify_key(
-        self, server_name, from_server, time_now_ms, verify_key
-    ):
-        """Stores a NACL verification key for the given server.
+    def store_server_verify_keys(self, from_server, ts_added_ms, verify_keys):
+        """Stores NACL verification keys for remote servers.
         Args:
-            server_name (str): The name of the server.
-            from_server (str): Where the verification key was looked up
-            time_now_ms (int): The time now in milliseconds
-            verify_key (nacl.signing.VerifyKey): The NACL verify key.
+            from_server (str): Where the verification keys were looked up
+            ts_added_ms (int): The time to record that the key was added
+            verify_keys (iterable[tuple[str, str, FetchKeyResult]]):
+                keys to be stored. Each entry is a triplet of
+                (server_name, key_id, key).
         """
-        key_id = "%s:%s" % (verify_key.alg, verify_key.version)
-
-        # XXX fix this to not need a lock (#3819)
-        def _txn(txn):
-            self._simple_upsert_txn(
-                txn,
-                table="server_signature_keys",
-                keyvalues={"server_name": server_name, "key_id": key_id},
-                values={
-                    "from_server": from_server,
-                    "ts_added_ms": time_now_ms,
-                    "verify_key": db_binary_type(verify_key.encode()),
-                },
+        key_values = []
+        value_values = []
+        invalidations = []
+        for server_name, key_id, fetch_result in verify_keys:
+            key_values.append((server_name, key_id))
+            value_values.append(
+                (
+                    from_server,
+                    ts_added_ms,
+                    fetch_result.valid_until_ts,
+                    db_binary_type(fetch_result.verify_key.encode()),
+                )
             )
             # invalidate takes a tuple corresponding to the params of
             # _get_server_verify_key. _get_server_verify_key only takes one
             # param, which is itself the 2-tuple (server_name, key_id).
-            txn.call_after(
-                self._get_server_verify_key.invalidate, ((server_name, key_id),)
-            )
-
-        return self.runInteraction("store_server_verify_key", _txn)
+            invalidations.append((server_name, key_id))
+
+        def _invalidate(res):
+            f = self._get_server_verify_key.invalidate
+            for i in invalidations:
+                f((i, ))
+            return res
+
+        return self.runInteraction(
+            "store_server_verify_keys",
+            self._simple_upsert_many_txn,
+            table="server_signature_keys",
+            key_names=("server_name", "key_id"),
+            key_values=key_values,
+            value_names=(
+                "from_server",
+                "ts_added_ms",
+                "ts_valid_until_ms",
+                "verify_key",
+            ),
+            value_values=value_values,
+        ).addCallback(_invalidate)
 
     def store_server_keys_json(
         self, server_name, key_id, from_server, ts_now_ms, ts_expires_ms, key_json_bytes
diff --git a/synapse/storage/relations.py b/synapse/storage/relations.py
new file mode 100644
index 0000000000..4c83800cca
--- /dev/null
+++ b/synapse/storage/relations.py
@@ -0,0 +1,476 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+import attr
+
+from twisted.internet import defer
+
+from synapse.api.constants import RelationTypes
+from synapse.api.errors import SynapseError
+from synapse.storage._base import SQLBaseStore
+from synapse.storage.stream import generate_pagination_where_clause
+from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
+
+logger = logging.getLogger(__name__)
+
+
+@attr.s
+class PaginationChunk(object):
+    """Returned by relation pagination APIs.
+
+    Attributes:
+        chunk (list): The rows returned by pagination
+        next_batch (Any|None): Token to fetch next set of results with, if
+            None then there are no more results.
+        prev_batch (Any|None): Token to fetch previous set of results with, if
+            None then there are no previous results.
+    """
+
+    chunk = attr.ib()
+    next_batch = attr.ib(default=None)
+    prev_batch = attr.ib(default=None)
+
+    def to_dict(self):
+        d = {"chunk": self.chunk}
+
+        if self.next_batch:
+            d["next_batch"] = self.next_batch.to_string()
+
+        if self.prev_batch:
+            d["prev_batch"] = self.prev_batch.to_string()
+
+        return d
+
+
+@attr.s(frozen=True, slots=True)
+class RelationPaginationToken(object):
+    """Pagination token for relation pagination API.
+
+    As the results are order by topological ordering, we can use the
+    `topological_ordering` and `stream_ordering` fields of the events at the
+    boundaries of the chunk as pagination tokens.
+
+    Attributes:
+        topological (int): The topological ordering of the boundary event
+        stream (int): The stream ordering of the boundary event.
+    """
+
+    topological = attr.ib()
+    stream = attr.ib()
+
+    @staticmethod
+    def from_string(string):
+        try:
+            t, s = string.split("-")
+            return RelationPaginationToken(int(t), int(s))
+        except ValueError:
+            raise SynapseError(400, "Invalid token")
+
+    def to_string(self):
+        return "%d-%d" % (self.topological, self.stream)
+
+    def as_tuple(self):
+        return attr.astuple(self)
+
+
+@attr.s(frozen=True, slots=True)
+class AggregationPaginationToken(object):
+    """Pagination token for relation aggregation pagination API.
+
+    As the results are order by count and then MAX(stream_ordering) of the
+    aggregation groups, we can just use them as our pagination token.
+
+    Attributes:
+        count (int): The count of relations in the boundar group.
+        stream (int): The MAX stream ordering in the boundary group.
+    """
+
+    count = attr.ib()
+    stream = attr.ib()
+
+    @staticmethod
+    def from_string(string):
+        try:
+            c, s = string.split("-")
+            return AggregationPaginationToken(int(c), int(s))
+        except ValueError:
+            raise SynapseError(400, "Invalid token")
+
+    def to_string(self):
+        return "%d-%d" % (self.count, self.stream)
+
+    def as_tuple(self):
+        return attr.astuple(self)
+
+
+class RelationsWorkerStore(SQLBaseStore):
+    @cached(tree=True)
+    def get_relations_for_event(
+        self,
+        event_id,
+        relation_type=None,
+        event_type=None,
+        aggregation_key=None,
+        limit=5,
+        direction="b",
+        from_token=None,
+        to_token=None,
+    ):
+        """Get a list of relations for an event, ordered by topological ordering.
+
+        Args:
+            event_id (str): Fetch events that relate to this event ID.
+            relation_type (str|None): Only fetch events with this relation
+                type, if given.
+            event_type (str|None): Only fetch events with this event type, if
+                given.
+            aggregation_key (str|None): Only fetch events with this aggregation
+                key, if given.
+            limit (int): Only fetch the most recent `limit` events.
+            direction (str): Whether to fetch the most recent first (`"b"`) or
+                the oldest first (`"f"`).
+            from_token (RelationPaginationToken|None): Fetch rows from the given
+                token, or from the start if None.
+            to_token (RelationPaginationToken|None): Fetch rows up to the given
+                token, or up to the end if None.
+
+        Returns:
+            Deferred[PaginationChunk]: List of event IDs that match relations
+            requested. The rows are of the form `{"event_id": "..."}`.
+        """
+
+        where_clause = ["relates_to_id = ?"]
+        where_args = [event_id]
+
+        if relation_type is not None:
+            where_clause.append("relation_type = ?")
+            where_args.append(relation_type)
+
+        if event_type is not None:
+            where_clause.append("type = ?")
+            where_args.append(event_type)
+
+        if aggregation_key:
+            where_clause.append("aggregation_key = ?")
+            where_args.append(aggregation_key)
+
+        pagination_clause = generate_pagination_where_clause(
+            direction=direction,
+            column_names=("topological_ordering", "stream_ordering"),
+            from_token=attr.astuple(from_token) if from_token else None,
+            to_token=attr.astuple(to_token) if to_token else None,
+            engine=self.database_engine,
+        )
+
+        if pagination_clause:
+            where_clause.append(pagination_clause)
+
+        if direction == "b":
+            order = "DESC"
+        else:
+            order = "ASC"
+
+        sql = """
+            SELECT event_id, topological_ordering, stream_ordering
+            FROM event_relations
+            INNER JOIN events USING (event_id)
+            WHERE %s
+            ORDER BY topological_ordering %s, stream_ordering %s
+            LIMIT ?
+        """ % (
+            " AND ".join(where_clause),
+            order,
+            order,
+        )
+
+        def _get_recent_references_for_event_txn(txn):
+            txn.execute(sql, where_args + [limit + 1])
+
+            last_topo_id = None
+            last_stream_id = None
+            events = []
+            for row in txn:
+                events.append({"event_id": row[0]})
+                last_topo_id = row[1]
+                last_stream_id = row[2]
+
+            next_batch = None
+            if len(events) > limit and last_topo_id and last_stream_id:
+                next_batch = RelationPaginationToken(last_topo_id, last_stream_id)
+
+            return PaginationChunk(
+                chunk=list(events[:limit]), next_batch=next_batch, prev_batch=from_token
+            )
+
+        return self.runInteraction(
+            "get_recent_references_for_event", _get_recent_references_for_event_txn
+        )
+
+    @cached(tree=True)
+    def get_aggregation_groups_for_event(
+        self,
+        event_id,
+        event_type=None,
+        limit=5,
+        direction="b",
+        from_token=None,
+        to_token=None,
+    ):
+        """Get a list of annotations on the event, grouped by event type and
+        aggregation key, sorted by count.
+
+        This is used e.g. to get the what and how many reactions have happend
+        on an event.
+
+        Args:
+            event_id (str): Fetch events that relate to this event ID.
+            event_type (str|None): Only fetch events with this event type, if
+                given.
+            limit (int): Only fetch the `limit` groups.
+            direction (str): Whether to fetch the highest count first (`"b"`) or
+                the lowest count first (`"f"`).
+            from_token (AggregationPaginationToken|None): Fetch rows from the
+                given token, or from the start if None.
+            to_token (AggregationPaginationToken|None): Fetch rows up to the
+                given token, or up to the end if None.
+
+
+        Returns:
+            Deferred[PaginationChunk]: List of groups of annotations that
+            match. Each row is a dict with `type`, `key` and `count` fields.
+        """
+
+        where_clause = ["relates_to_id = ?", "relation_type = ?"]
+        where_args = [event_id, RelationTypes.ANNOTATION]
+
+        if event_type:
+            where_clause.append("type = ?")
+            where_args.append(event_type)
+
+        having_clause = generate_pagination_where_clause(
+            direction=direction,
+            column_names=("COUNT(*)", "MAX(stream_ordering)"),
+            from_token=attr.astuple(from_token) if from_token else None,
+            to_token=attr.astuple(to_token) if to_token else None,
+            engine=self.database_engine,
+        )
+
+        if direction == "b":
+            order = "DESC"
+        else:
+            order = "ASC"
+
+        if having_clause:
+            having_clause = "HAVING " + having_clause
+        else:
+            having_clause = ""
+
+        sql = """
+            SELECT type, aggregation_key, COUNT(DISTINCT sender), MAX(stream_ordering)
+            FROM event_relations
+            INNER JOIN events USING (event_id)
+            WHERE {where_clause}
+            GROUP BY relation_type, type, aggregation_key
+            {having_clause}
+            ORDER BY COUNT(*) {order}, MAX(stream_ordering) {order}
+            LIMIT ?
+        """.format(
+            where_clause=" AND ".join(where_clause),
+            order=order,
+            having_clause=having_clause,
+        )
+
+        def _get_aggregation_groups_for_event_txn(txn):
+            txn.execute(sql, where_args + [limit + 1])
+
+            next_batch = None
+            events = []
+            for row in txn:
+                events.append({"type": row[0], "key": row[1], "count": row[2]})
+                next_batch = AggregationPaginationToken(row[2], row[3])
+
+            if len(events) <= limit:
+                next_batch = None
+
+            return PaginationChunk(
+                chunk=list(events[:limit]), next_batch=next_batch, prev_batch=from_token
+            )
+
+        return self.runInteraction(
+            "get_aggregation_groups_for_event", _get_aggregation_groups_for_event_txn
+        )
+
+    @cachedInlineCallbacks()
+    def get_applicable_edit(self, event_id):
+        """Get the most recent edit (if any) that has happened for the given
+        event.
+
+        Correctly handles checking whether edits were allowed to happen.
+
+        Args:
+            event_id (str): The original event ID
+
+        Returns:
+            Deferred[EventBase|None]: Returns the most recent edit, if any.
+        """
+
+        # We only allow edits for `m.room.message` events that have the same sender
+        # and event type. We can't assert these things during regular event auth so
+        # we have to do the checks post hoc.
+
+        # Fetches latest edit that has the same type and sender as the
+        # original, and is an `m.room.message`.
+        sql = """
+            SELECT edit.event_id FROM events AS edit
+            INNER JOIN event_relations USING (event_id)
+            INNER JOIN events AS original ON
+                original.event_id = relates_to_id
+                AND edit.type = original.type
+                AND edit.sender = original.sender
+            WHERE
+                relates_to_id = ?
+                AND relation_type = ?
+                AND edit.type = 'm.room.message'
+            ORDER by edit.origin_server_ts DESC, edit.event_id DESC
+            LIMIT 1
+        """
+
+        def _get_applicable_edit_txn(txn):
+            txn.execute(sql, (event_id, RelationTypes.REPLACE))
+            row = txn.fetchone()
+            if row:
+                return row[0]
+
+        edit_id = yield self.runInteraction(
+            "get_applicable_edit", _get_applicable_edit_txn
+        )
+
+        if not edit_id:
+            return
+
+        edit_event = yield self.get_event(edit_id, allow_none=True)
+        defer.returnValue(edit_event)
+
+    def has_user_annotated_event(self, parent_id, event_type, aggregation_key, sender):
+        """Check if a user has already annotated an event with the same key
+        (e.g. already liked an event).
+
+        Args:
+            parent_id (str): The event being annotated
+            event_type (str): The event type of the annotation
+            aggregation_key (str): The aggregation key of the annotation
+            sender (str): The sender of the annotation
+
+        Returns:
+            Deferred[bool]
+        """
+
+        sql = """
+            SELECT 1 FROM event_relations
+            INNER JOIN events USING (event_id)
+            WHERE
+                relates_to_id = ?
+                AND relation_type = ?
+                AND type = ?
+                AND sender = ?
+                AND aggregation_key = ?
+            LIMIT 1;
+        """
+
+        def _get_if_user_has_annotated_event(txn):
+            txn.execute(
+                sql,
+                (
+                    parent_id,
+                    RelationTypes.ANNOTATION,
+                    event_type,
+                    sender,
+                    aggregation_key,
+                ),
+            )
+
+            return bool(txn.fetchone())
+
+        return self.runInteraction(
+            "get_if_user_has_annotated_event", _get_if_user_has_annotated_event
+        )
+
+
+class RelationsStore(RelationsWorkerStore):
+    def _handle_event_relations(self, txn, event):
+        """Handles inserting relation data during peristence of events
+
+        Args:
+            txn
+            event (EventBase)
+        """
+        relation = event.content.get("m.relates_to")
+        if not relation:
+            # No relations
+            return
+
+        rel_type = relation.get("rel_type")
+        if rel_type not in (
+            RelationTypes.ANNOTATION,
+            RelationTypes.REFERENCE,
+            RelationTypes.REPLACE,
+        ):
+            # Unknown relation type
+            return
+
+        parent_id = relation.get("event_id")
+        if not parent_id:
+            # Invalid relation
+            return
+
+        aggregation_key = relation.get("key")
+
+        self._simple_insert_txn(
+            txn,
+            table="event_relations",
+            values={
+                "event_id": event.event_id,
+                "relates_to_id": parent_id,
+                "relation_type": rel_type,
+                "aggregation_key": aggregation_key,
+            },
+        )
+
+        txn.call_after(self.get_relations_for_event.invalidate_many, (parent_id,))
+        txn.call_after(
+            self.get_aggregation_groups_for_event.invalidate_many, (parent_id,)
+        )
+
+        if rel_type == RelationTypes.REPLACE:
+            txn.call_after(self.get_applicable_edit.invalidate, (parent_id,))
+
+    def _handle_redaction(self, txn, redacted_event_id):
+        """Handles receiving a redaction and checking whether we need to remove
+        any redacted relations from the database.
+
+        Args:
+            txn
+            redacted_event_id (str): The event that was redacted.
+        """
+
+        self._simple_delete_txn(
+            txn,
+            table="event_relations",
+            keyvalues={
+                "event_id": redacted_event_id,
+            }
+        )
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 57df17bcc2..4bd1669458 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -142,6 +142,38 @@ class RoomMemberWorkerStore(EventsWorkerStore):
 
         return self.runInteraction("get_room_summary", _get_room_summary_txn)
 
+    def _get_user_count_in_room_txn(self, txn, room_id, membership):
+        """
+        See get_user_count_in_room.
+        """
+        sql = (
+            "SELECT count(*) FROM room_memberships as m"
+            " INNER JOIN current_state_events as c"
+            " ON m.event_id = c.event_id "
+            " AND m.room_id = c.room_id "
+            " AND m.user_id = c.state_key"
+            " WHERE c.type = 'm.room.member' AND c.room_id = ? AND m.membership = ?"
+        )
+
+        txn.execute(sql, (room_id, membership))
+        row = txn.fetchone()
+        return row[0]
+
+    def get_user_count_in_room(self, room_id, membership):
+        """
+        Get the user count in a room with a particular membership.
+
+        Args:
+            room_id (str)
+            membership (Membership)
+
+        Returns:
+            Deferred[int]
+        """
+        return self.runInteraction(
+            "get_users_in_room", self._get_user_count_in_room_txn, room_id, membership
+        )
+
     @cached()
     def get_invited_rooms_for_user(self, user_id):
         """ Get all the rooms the user is invited to
diff --git a/synapse/storage/schema/delta/54/add_validity_to_server_keys.sql b/synapse/storage/schema/delta/54/add_validity_to_server_keys.sql
new file mode 100644
index 0000000000..c01aa9d2d9
--- /dev/null
+++ b/synapse/storage/schema/delta/54/add_validity_to_server_keys.sql
@@ -0,0 +1,23 @@
+/* Copyright 2019 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* When we can use this key until, before we have to refresh it. */
+ALTER TABLE server_signature_keys ADD COLUMN ts_valid_until_ms BIGINT;
+
+UPDATE server_signature_keys SET ts_valid_until_ms = (
+    SELECT MAX(ts_valid_until_ms) FROM server_keys_json skj WHERE
+        skj.server_name = server_signature_keys.server_name AND
+        skj.key_id = server_signature_keys.key_id
+);
diff --git a/synapse/storage/schema/delta/54/relations.sql b/synapse/storage/schema/delta/54/relations.sql
new file mode 100644
index 0000000000..134862b870
--- /dev/null
+++ b/synapse/storage/schema/delta/54/relations.sql
@@ -0,0 +1,27 @@
+/* Copyright 2019 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- Tracks related events, like reactions, replies, edits, etc. Note that things
+-- in this table are not necessarily "valid", e.g. it may contain edits from
+-- people who don't have power to edit other peoples events.
+CREATE TABLE IF NOT EXISTS event_relations (
+    event_id TEXT NOT NULL,
+    relates_to_id TEXT NOT NULL,
+    relation_type TEXT NOT NULL,
+    aggregation_key TEXT
+);
+
+CREATE UNIQUE INDEX event_relations_id ON event_relations(event_id);
+CREATE INDEX event_relations_relates ON event_relations(relates_to_id, relation_type, aggregation_key);
diff --git a/synapse/storage/schema/delta/54/stats.sql b/synapse/storage/schema/delta/54/stats.sql
new file mode 100644
index 0000000000..652e58308e
--- /dev/null
+++ b/synapse/storage/schema/delta/54/stats.sql
@@ -0,0 +1,80 @@
+/* Copyright 2018 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+CREATE TABLE stats_stream_pos (
+    Lock CHAR(1) NOT NULL DEFAULT 'X' UNIQUE,  -- Makes sure this table only has one row.
+    stream_id BIGINT,
+    CHECK (Lock='X')
+);
+
+INSERT INTO stats_stream_pos (stream_id) VALUES (null);
+
+CREATE TABLE user_stats (
+    user_id TEXT NOT NULL,
+    ts BIGINT NOT NULL,
+    bucket_size INT NOT NULL,
+    public_rooms INT NOT NULL,
+    private_rooms INT NOT NULL
+);
+
+CREATE UNIQUE INDEX user_stats_user_ts ON user_stats(user_id, ts);
+
+CREATE TABLE room_stats (
+    room_id TEXT NOT NULL,
+    ts BIGINT NOT NULL,
+    bucket_size INT NOT NULL,
+    current_state_events INT NOT NULL,
+    joined_members INT NOT NULL,
+    invited_members INT NOT NULL,
+    left_members INT NOT NULL,
+    banned_members INT NOT NULL,
+    state_events INT NOT NULL
+);
+
+CREATE UNIQUE INDEX room_stats_room_ts ON room_stats(room_id, ts);
+
+-- cache of current room state; useful for the publicRooms list
+CREATE TABLE room_state (
+    room_id TEXT NOT NULL,
+    join_rules TEXT,
+    history_visibility TEXT,
+    encryption TEXT,
+    name TEXT,
+    topic TEXT,
+    avatar TEXT,
+    canonical_alias TEXT
+    -- get aliases straight from the right table
+);
+
+CREATE UNIQUE INDEX room_state_room ON room_state(room_id);
+
+CREATE TABLE room_stats_earliest_token (
+    room_id TEXT NOT NULL,
+    token BIGINT NOT NULL
+);
+
+CREATE UNIQUE INDEX room_stats_earliest_token_idx ON room_stats_earliest_token(room_id);
+
+-- Set up staging tables
+INSERT INTO background_updates (update_name, progress_json) VALUES
+    ('populate_stats_createtables', '{}');
+
+-- Run through each room and update stats
+INSERT INTO background_updates (update_name, progress_json, depends_on) VALUES
+    ('populate_stats_process_rooms', '{}', 'populate_stats_createtables');
+
+-- Clean up staging tables
+INSERT INTO background_updates (update_name, progress_json, depends_on) VALUES
+    ('populate_stats_cleanup', '{}', 'populate_stats_process_rooms');
diff --git a/synapse/storage/state_deltas.py b/synapse/storage/state_deltas.py
index 31a0279b18..5fdb442104 100644
--- a/synapse/storage/state_deltas.py
+++ b/synapse/storage/state_deltas.py
@@ -84,10 +84,16 @@ class StateDeltasStore(SQLBaseStore):
             "get_current_state_deltas", get_current_state_deltas_txn
         )
 
-    def get_max_stream_id_in_current_state_deltas(self):
-        return self._simple_select_one_onecol(
+    def _get_max_stream_id_in_current_state_deltas_txn(self, txn):
+        return self._simple_select_one_onecol_txn(
+            txn,
             table="current_state_delta_stream",
             keyvalues={},
             retcol="COALESCE(MAX(stream_id), -1)",
-            desc="get_max_stream_id_in_current_state_deltas",
+        )
+
+    def get_max_stream_id_in_current_state_deltas(self):
+        return self.runInteraction(
+            "get_max_stream_id_in_current_state_deltas",
+            self._get_max_stream_id_in_current_state_deltas_txn,
         )
diff --git a/synapse/storage/stats.py b/synapse/storage/stats.py
new file mode 100644
index 0000000000..eb0ced5b5e
--- /dev/null
+++ b/synapse/storage/stats.py
@@ -0,0 +1,450 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018, 2019 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+from twisted.internet import defer
+
+from synapse.api.constants import EventTypes, Membership
+from synapse.storage.state_deltas import StateDeltasStore
+from synapse.util.caches.descriptors import cached
+
+logger = logging.getLogger(__name__)
+
+# these fields track absolutes (e.g. total number of rooms on the server)
+ABSOLUTE_STATS_FIELDS = {
+    "room": (
+        "current_state_events",
+        "joined_members",
+        "invited_members",
+        "left_members",
+        "banned_members",
+        "state_events",
+    ),
+    "user": ("public_rooms", "private_rooms"),
+}
+
+TYPE_TO_ROOM = {"room": ("room_stats", "room_id"), "user": ("user_stats", "user_id")}
+
+TEMP_TABLE = "_temp_populate_stats"
+
+
+class StatsStore(StateDeltasStore):
+    def __init__(self, db_conn, hs):
+        super(StatsStore, self).__init__(db_conn, hs)
+
+        self.server_name = hs.hostname
+        self.clock = self.hs.get_clock()
+        self.stats_enabled = hs.config.stats_enabled
+        self.stats_bucket_size = hs.config.stats_bucket_size
+
+        self.register_background_update_handler(
+            "populate_stats_createtables", self._populate_stats_createtables
+        )
+        self.register_background_update_handler(
+            "populate_stats_process_rooms", self._populate_stats_process_rooms
+        )
+        self.register_background_update_handler(
+            "populate_stats_cleanup", self._populate_stats_cleanup
+        )
+
+    @defer.inlineCallbacks
+    def _populate_stats_createtables(self, progress, batch_size):
+
+        if not self.stats_enabled:
+            yield self._end_background_update("populate_stats_createtables")
+            defer.returnValue(1)
+
+        # Get all the rooms that we want to process.
+        def _make_staging_area(txn):
+            sql = (
+                "CREATE TABLE IF NOT EXISTS "
+                + TEMP_TABLE
+                + "_rooms(room_id TEXT NOT NULL, events BIGINT NOT NULL)"
+            )
+            txn.execute(sql)
+
+            sql = (
+                "CREATE TABLE IF NOT EXISTS "
+                + TEMP_TABLE
+                + "_position(position TEXT NOT NULL)"
+            )
+            txn.execute(sql)
+
+            # Get rooms we want to process from the database
+            sql = """
+                SELECT room_id, count(*) FROM current_state_events
+                GROUP BY room_id
+            """
+            txn.execute(sql)
+            rooms = [{"room_id": x[0], "events": x[1]} for x in txn.fetchall()]
+            self._simple_insert_many_txn(txn, TEMP_TABLE + "_rooms", rooms)
+            del rooms
+
+        new_pos = yield self.get_max_stream_id_in_current_state_deltas()
+        yield self.runInteraction("populate_stats_temp_build", _make_staging_area)
+        yield self._simple_insert(TEMP_TABLE + "_position", {"position": new_pos})
+        self.get_earliest_token_for_room_stats.invalidate_all()
+
+        yield self._end_background_update("populate_stats_createtables")
+        defer.returnValue(1)
+
+    @defer.inlineCallbacks
+    def _populate_stats_cleanup(self, progress, batch_size):
+        """
+        Update the user directory stream position, then clean up the old tables.
+        """
+        if not self.stats_enabled:
+            yield self._end_background_update("populate_stats_cleanup")
+            defer.returnValue(1)
+
+        position = yield self._simple_select_one_onecol(
+            TEMP_TABLE + "_position", None, "position"
+        )
+        yield self.update_stats_stream_pos(position)
+
+        def _delete_staging_area(txn):
+            txn.execute("DROP TABLE IF EXISTS " + TEMP_TABLE + "_rooms")
+            txn.execute("DROP TABLE IF EXISTS " + TEMP_TABLE + "_position")
+
+        yield self.runInteraction("populate_stats_cleanup", _delete_staging_area)
+
+        yield self._end_background_update("populate_stats_cleanup")
+        defer.returnValue(1)
+
+    @defer.inlineCallbacks
+    def _populate_stats_process_rooms(self, progress, batch_size):
+
+        if not self.stats_enabled:
+            yield self._end_background_update("populate_stats_process_rooms")
+            defer.returnValue(1)
+
+        # If we don't have progress filed, delete everything.
+        if not progress:
+            yield self.delete_all_stats()
+
+        def _get_next_batch(txn):
+            # Only fetch 250 rooms, so we don't fetch too many at once, even
+            # if those 250 rooms have less than batch_size state events.
+            sql = """
+                SELECT room_id, events FROM %s_rooms
+                ORDER BY events DESC
+                LIMIT 250
+            """ % (
+                TEMP_TABLE,
+            )
+            txn.execute(sql)
+            rooms_to_work_on = txn.fetchall()
+
+            if not rooms_to_work_on:
+                return None
+
+            # Get how many are left to process, so we can give status on how
+            # far we are in processing
+            txn.execute("SELECT COUNT(*) FROM " + TEMP_TABLE + "_rooms")
+            progress["remaining"] = txn.fetchone()[0]
+
+            return rooms_to_work_on
+
+        rooms_to_work_on = yield self.runInteraction(
+            "populate_stats_temp_read", _get_next_batch
+        )
+
+        # No more rooms -- complete the transaction.
+        if not rooms_to_work_on:
+            yield self._end_background_update("populate_stats_process_rooms")
+            defer.returnValue(1)
+
+        logger.info(
+            "Processing the next %d rooms of %d remaining",
+            len(rooms_to_work_on), progress["remaining"],
+        )
+
+        # Number of state events we've processed by going through each room
+        processed_event_count = 0
+
+        for room_id, event_count in rooms_to_work_on:
+
+            current_state_ids = yield self.get_current_state_ids(room_id)
+
+            join_rules = yield self.get_event(
+                current_state_ids.get((EventTypes.JoinRules, "")), allow_none=True
+            )
+            history_visibility = yield self.get_event(
+                current_state_ids.get((EventTypes.RoomHistoryVisibility, "")),
+                allow_none=True,
+            )
+            encryption = yield self.get_event(
+                current_state_ids.get((EventTypes.RoomEncryption, "")), allow_none=True
+            )
+            name = yield self.get_event(
+                current_state_ids.get((EventTypes.Name, "")), allow_none=True
+            )
+            topic = yield self.get_event(
+                current_state_ids.get((EventTypes.Topic, "")), allow_none=True
+            )
+            avatar = yield self.get_event(
+                current_state_ids.get((EventTypes.RoomAvatar, "")), allow_none=True
+            )
+            canonical_alias = yield self.get_event(
+                current_state_ids.get((EventTypes.CanonicalAlias, "")), allow_none=True
+            )
+
+            def _or_none(x, arg):
+                if x:
+                    return x.content.get(arg)
+                return None
+
+            yield self.update_room_state(
+                room_id,
+                {
+                    "join_rules": _or_none(join_rules, "join_rule"),
+                    "history_visibility": _or_none(
+                        history_visibility, "history_visibility"
+                    ),
+                    "encryption": _or_none(encryption, "algorithm"),
+                    "name": _or_none(name, "name"),
+                    "topic": _or_none(topic, "topic"),
+                    "avatar": _or_none(avatar, "url"),
+                    "canonical_alias": _or_none(canonical_alias, "alias"),
+                },
+            )
+
+            now = self.hs.get_reactor().seconds()
+
+            # quantise time to the nearest bucket
+            now = (now // self.stats_bucket_size) * self.stats_bucket_size
+
+            def _fetch_data(txn):
+
+                # Get the current token of the room
+                current_token = self._get_max_stream_id_in_current_state_deltas_txn(txn)
+
+                current_state_events = len(current_state_ids)
+                joined_members = self._get_user_count_in_room_txn(
+                    txn, room_id, Membership.JOIN
+                )
+                invited_members = self._get_user_count_in_room_txn(
+                    txn, room_id, Membership.INVITE
+                )
+                left_members = self._get_user_count_in_room_txn(
+                    txn, room_id, Membership.LEAVE
+                )
+                banned_members = self._get_user_count_in_room_txn(
+                    txn, room_id, Membership.BAN
+                )
+                total_state_events = self._get_total_state_event_counts_txn(
+                    txn, room_id
+                )
+
+                self._update_stats_txn(
+                    txn,
+                    "room",
+                    room_id,
+                    now,
+                    {
+                        "bucket_size": self.stats_bucket_size,
+                        "current_state_events": current_state_events,
+                        "joined_members": joined_members,
+                        "invited_members": invited_members,
+                        "left_members": left_members,
+                        "banned_members": banned_members,
+                        "state_events": total_state_events,
+                    },
+                )
+                self._simple_insert_txn(
+                    txn,
+                    "room_stats_earliest_token",
+                    {"room_id": room_id, "token": current_token},
+                )
+
+            yield self.runInteraction("update_room_stats", _fetch_data)
+
+            # We've finished a room. Delete it from the table.
+            yield self._simple_delete_one(TEMP_TABLE + "_rooms", {"room_id": room_id})
+            # Update the remaining counter.
+            progress["remaining"] -= 1
+            yield self.runInteraction(
+                "populate_stats",
+                self._background_update_progress_txn,
+                "populate_stats_process_rooms",
+                progress,
+            )
+
+            processed_event_count += event_count
+
+            if processed_event_count > batch_size:
+                # Don't process any more rooms, we've hit our batch size.
+                defer.returnValue(processed_event_count)
+
+        defer.returnValue(processed_event_count)
+
+    def delete_all_stats(self):
+        """
+        Delete all statistics records.
+        """
+
+        def _delete_all_stats_txn(txn):
+            txn.execute("DELETE FROM room_state")
+            txn.execute("DELETE FROM room_stats")
+            txn.execute("DELETE FROM room_stats_earliest_token")
+            txn.execute("DELETE FROM user_stats")
+
+        return self.runInteraction("delete_all_stats", _delete_all_stats_txn)
+
+    def get_stats_stream_pos(self):
+        return self._simple_select_one_onecol(
+            table="stats_stream_pos",
+            keyvalues={},
+            retcol="stream_id",
+            desc="stats_stream_pos",
+        )
+
+    def update_stats_stream_pos(self, stream_id):
+        return self._simple_update_one(
+            table="stats_stream_pos",
+            keyvalues={},
+            updatevalues={"stream_id": stream_id},
+            desc="update_stats_stream_pos",
+        )
+
+    def update_room_state(self, room_id, fields):
+        """
+        Args:
+            room_id (str)
+            fields (dict[str:Any])
+        """
+        return self._simple_upsert(
+            table="room_state",
+            keyvalues={"room_id": room_id},
+            values=fields,
+            desc="update_room_state",
+        )
+
+    def get_deltas_for_room(self, room_id, start, size=100):
+        """
+        Get statistics deltas for a given room.
+
+        Args:
+            room_id (str)
+            start (int): Pagination start. Number of entries, not timestamp.
+            size (int): How many entries to return.
+
+        Returns:
+            Deferred[list[dict]], where the dict has the keys of
+            ABSOLUTE_STATS_FIELDS["room"] and "ts".
+        """
+        return self._simple_select_list_paginate(
+            "room_stats",
+            {"room_id": room_id},
+            "ts",
+            start,
+            size,
+            retcols=(list(ABSOLUTE_STATS_FIELDS["room"]) + ["ts"]),
+            order_direction="DESC",
+        )
+
+    def get_all_room_state(self):
+        return self._simple_select_list(
+            "room_state", None, retcols=("name", "topic", "canonical_alias")
+        )
+
+    @cached()
+    def get_earliest_token_for_room_stats(self, room_id):
+        """
+        Fetch the "earliest token". This is used by the room stats delta
+        processor to ignore deltas that have been processed between the
+        start of the background task and any particular room's stats
+        being calculated.
+
+        Returns:
+            Deferred[int]
+        """
+        return self._simple_select_one_onecol(
+            "room_stats_earliest_token",
+            {"room_id": room_id},
+            retcol="token",
+            allow_none=True,
+        )
+
+    def update_stats(self, stats_type, stats_id, ts, fields):
+        table, id_col = TYPE_TO_ROOM[stats_type]
+        return self._simple_upsert(
+            table=table,
+            keyvalues={id_col: stats_id, "ts": ts},
+            values=fields,
+            desc="update_stats",
+        )
+
+    def _update_stats_txn(self, txn, stats_type, stats_id, ts, fields):
+        table, id_col = TYPE_TO_ROOM[stats_type]
+        return self._simple_upsert_txn(
+            txn, table=table, keyvalues={id_col: stats_id, "ts": ts}, values=fields
+        )
+
+    def update_stats_delta(self, ts, stats_type, stats_id, field, value):
+        def _update_stats_delta(txn):
+            table, id_col = TYPE_TO_ROOM[stats_type]
+
+            sql = (
+                "SELECT * FROM %s"
+                " WHERE %s=? and ts=("
+                "  SELECT MAX(ts) FROM %s"
+                "  WHERE %s=?"
+                ")"
+            ) % (table, id_col, table, id_col)
+            txn.execute(sql, (stats_id, stats_id))
+            rows = self.cursor_to_dict(txn)
+            if len(rows) == 0:
+                # silently skip as we don't have anything to apply a delta to yet.
+                # this tries to minimise any race between the initial sync and
+                # subsequent deltas arriving.
+                return
+
+            current_ts = ts
+            latest_ts = rows[0]["ts"]
+            if current_ts < latest_ts:
+                # This one is in the past, but we're just encountering it now.
+                # Mark it as part of the current bucket.
+                current_ts = latest_ts
+            elif ts != latest_ts:
+                # we have to copy our absolute counters over to the new entry.
+                values = {
+                    key: rows[0][key] for key in ABSOLUTE_STATS_FIELDS[stats_type]
+                }
+                values[id_col] = stats_id
+                values["ts"] = ts
+                values["bucket_size"] = self.stats_bucket_size
+
+                self._simple_insert_txn(txn, table=table, values=values)
+
+            # actually update the new value
+            if stats_type in ABSOLUTE_STATS_FIELDS[stats_type]:
+                self._simple_update_txn(
+                    txn,
+                    table=table,
+                    keyvalues={id_col: stats_id, "ts": current_ts},
+                    updatevalues={field: value},
+                )
+            else:
+                sql = ("UPDATE %s SET %s=%s+? WHERE %s=? AND ts=?") % (
+                    table,
+                    field,
+                    field,
+                    id_col,
+                )
+                txn.execute(sql, (value, stats_id, current_ts))
+
+        return self.runInteraction("update_stats_delta", _update_stats_delta)
diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py
index d105b6b17d..529ad4ea79 100644
--- a/synapse/storage/stream.py
+++ b/synapse/storage/stream.py
@@ -64,59 +64,135 @@ _EventDictReturn = namedtuple(
 )
 
 
-def lower_bound(token, engine, inclusive=False):
-    inclusive = "=" if inclusive else ""
-    if token.topological is None:
-        return "(%d <%s %s)" % (token.stream, inclusive, "stream_ordering")
-    else:
-        if isinstance(engine, PostgresEngine):
-            # Postgres doesn't optimise ``(x < a) OR (x=a AND y<b)`` as well
-            # as it optimises ``(x,y) < (a,b)`` on multicolumn indexes. So we
-            # use the later form when running against postgres.
-            return "((%d,%d) <%s (%s,%s))" % (
-                token.topological,
-                token.stream,
-                inclusive,
-                "topological_ordering",
-                "stream_ordering",
+def generate_pagination_where_clause(
+    direction, column_names, from_token, to_token, engine,
+):
+    """Creates an SQL expression to bound the columns by the pagination
+    tokens.
+
+    For example creates an SQL expression like:
+
+        (6, 7) >= (topological_ordering, stream_ordering)
+        AND (5, 3) < (topological_ordering, stream_ordering)
+
+    would be generated for dir=b, from_token=(6, 7) and to_token=(5, 3).
+
+    Note that tokens are considered to be after the row they are in, e.g. if
+    a row A has a token T, then we consider A to be before T. This convention
+    is important when figuring out inequalities for the generated SQL, and
+    produces the following result:
+        - If paginating forwards then we exclude any rows matching the from
+          token, but include those that match the to token.
+        - If paginating backwards then we include any rows matching the from
+          token, but include those that match the to token.
+
+    Args:
+        direction (str): Whether we're paginating backwards("b") or
+            forwards ("f").
+        column_names (tuple[str, str]): The column names to bound. Must *not*
+            be user defined as these get inserted directly into the SQL
+            statement without escapes.
+        from_token (tuple[int, int]|None): The start point for the pagination.
+            This is an exclusive minimum bound if direction is "f", and an
+            inclusive maximum bound if direction is "b".
+        to_token (tuple[int, int]|None): The endpoint point for the pagination.
+            This is an inclusive maximum bound if direction is "f", and an
+            exclusive minimum bound if direction is "b".
+        engine: The database engine to generate the clauses for
+
+    Returns:
+        str: The sql expression
+    """
+    assert direction in ("b", "f")
+
+    where_clause = []
+    if from_token:
+        where_clause.append(
+            _make_generic_sql_bound(
+                bound=">=" if direction == "b" else "<",
+                column_names=column_names,
+                values=from_token,
+                engine=engine,
             )
-        return "(%d < %s OR (%d = %s AND %d <%s %s))" % (
-            token.topological,
-            "topological_ordering",
-            token.topological,
-            "topological_ordering",
-            token.stream,
-            inclusive,
-            "stream_ordering",
-        )
-
-
-def upper_bound(token, engine, inclusive=True):
-    inclusive = "=" if inclusive else ""
-    if token.topological is None:
-        return "(%d >%s %s)" % (token.stream, inclusive, "stream_ordering")
-    else:
-        if isinstance(engine, PostgresEngine):
-            # Postgres doesn't optimise ``(x > a) OR (x=a AND y>b)`` as well
-            # as it optimises ``(x,y) > (a,b)`` on multicolumn indexes. So we
-            # use the later form when running against postgres.
-            return "((%d,%d) >%s (%s,%s))" % (
-                token.topological,
-                token.stream,
-                inclusive,
-                "topological_ordering",
-                "stream_ordering",
+        )
+
+    if to_token:
+        where_clause.append(
+            _make_generic_sql_bound(
+                bound="<" if direction == "b" else ">=",
+                column_names=column_names,
+                values=to_token,
+                engine=engine,
             )
-        return "(%d > %s OR (%d = %s AND %d >%s %s))" % (
-            token.topological,
-            "topological_ordering",
-            token.topological,
-            "topological_ordering",
-            token.stream,
-            inclusive,
-            "stream_ordering",
         )
 
+    return " AND ".join(where_clause)
+
+
+def _make_generic_sql_bound(bound, column_names, values, engine):
+    """Create an SQL expression that bounds the given column names by the
+    values, e.g. create the equivalent of `(1, 2) < (col1, col2)`.
+
+    Only works with two columns.
+
+    Older versions of SQLite don't support that syntax so we have to expand it
+    out manually.
+
+    Args:
+        bound (str): The comparison operator to use. One of ">", "<", ">=",
+            "<=", where the values are on the left and columns on the right.
+        names (tuple[str, str]): The column names. Must *not* be user defined
+            as these get inserted directly into the SQL statement without
+            escapes.
+        values (tuple[int|None, int]): The values to bound the columns by. If
+            the first value is None then only creates a bound on the second
+            column.
+        engine: The database engine to generate the SQL for
+
+    Returns:
+        str
+    """
+
+    assert(bound in (">", "<", ">=", "<="))
+
+    name1, name2 = column_names
+    val1, val2 = values
+
+    if val1 is None:
+        val2 = int(val2)
+        return "(%d %s %s)" % (val2, bound, name2)
+
+    val1 = int(val1)
+    val2 = int(val2)
+
+    if isinstance(engine, PostgresEngine):
+        # Postgres doesn't optimise ``(x < a) OR (x=a AND y<b)`` as well
+        # as it optimises ``(x,y) < (a,b)`` on multicolumn indexes. So we
+        # use the later form when running against postgres.
+        return "((%d,%d) %s (%s,%s))" % (
+            val1, val2,
+            bound,
+            name1, name2,
+        )
+
+    # We want to generate queries of e.g. the form:
+    #
+    #   (val1 < name1 OR (val1 = name1 AND val2 <= name2))
+    #
+    # which is equivalent to (val1, val2) < (name1, name2)
+
+    return """(
+        {val1:d} {strict_bound} {name1}
+        OR ({val1:d} = {name1} AND {val2:d} {bound} {name2})
+    )""".format(
+        name1=name1,
+        val1=val1,
+        name2=name2,
+        val2=val2,
+        strict_bound=bound[0],  # The first bound must always be strict equality here
+        bound=bound,
+    )
+
 
 def filter_to_clause(event_filter):
     # NB: This may create SQL clauses that don't optimise well (and we don't
@@ -762,20 +838,16 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
         args = [False, room_id]
         if direction == 'b':
             order = "DESC"
-            bounds = upper_bound(from_token, self.database_engine)
-            if to_token:
-                bounds = "%s AND %s" % (
-                    bounds,
-                    lower_bound(to_token, self.database_engine),
-                )
         else:
             order = "ASC"
-            bounds = lower_bound(from_token, self.database_engine)
-            if to_token:
-                bounds = "%s AND %s" % (
-                    bounds,
-                    upper_bound(to_token, self.database_engine),
-                )
+
+        bounds = generate_pagination_where_clause(
+            direction=direction,
+            column_names=("topological_ordering", "stream_ordering"),
+            from_token=from_token,
+            to_token=to_token,
+            engine=self.database_engine,
+        )
 
         filter_clause, filter_args = filter_to_clause(event_filter)