Merge pull request #536 from matrix-org/erikj/sync

Make /sync "better".

10 files changed, 501 insertions, 324 deletions

diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index b73ad62147..82c8cb5f0c 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -16,7 +16,7 @@
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership
-from synapse.api.errors import SynapseError, AuthError, Codes
+from synapse.api.errors import AuthError, Codes
 from synapse.streams.config import PaginationConfig
 from synapse.events.utils import serialize_event
 from synapse.events.validator import EventValidator
@@ -119,9 +119,12 @@ class MessageHandler(BaseHandler):
         if source_config.direction == 'b':
             # if we're going backwards, we might need to backfill. This
             # requires that we have a topo token.
-            if room_token.topological is None:
-                raise SynapseError(400, "Invalid token: cannot paginate "
-                                        "backwards from a stream token")
+            if room_token.topological:
+                max_topo = room_token.topological
+            else:
+                max_topo = yield self.store.get_max_topological_token_for_stream_and_room(
+                    room_id, room_token.stream
+                )
 
             if membership == Membership.LEAVE:
                 # If they have left the room then clamp the token to be before
@@ -131,11 +134,11 @@ class MessageHandler(BaseHandler):
                     member_event_id
                 )
                 leave_token = RoomStreamToken.parse(leave_token)
-                if leave_token.topological < room_token.topological:
+                if leave_token.topological < max_topo:
                     source_config.from_key = str(leave_token)
 
             yield self.hs.get_handlers().federation_handler.maybe_backfill(
-                room_id, room_token.topological
+                room_id, max_topo
             )
 
         events, next_key = yield data_source.get_pagination_rows(
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 328c049b03..51ec4702db 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -72,7 +72,7 @@ class JoinedSyncResult(collections.namedtuple("JoinedSyncResult", [
         )
 
 
-class ArchivedSyncResult(collections.namedtuple("JoinedSyncResult", [
+class ArchivedSyncResult(collections.namedtuple("ArchivedSyncResult", [
     "room_id",            # str
     "timeline",           # TimelineBatch
     "state",              # dict[(str, str), FrozenEvent]
@@ -298,46 +298,19 @@ class SyncHandler(BaseHandler):
             room_id, sync_config, now_token, since_token=timeline_since_token
         )
 
-        notifs = yield self.unread_notifs_for_room_id(
-            room_id, sync_config, ephemeral_by_room
-        )
-
-        unread_notifications = {}
-        if notifs is not None:
-            unread_notifications["notification_count"] = len(notifs)
-            unread_notifications["highlight_count"] = len([
-                1 for notif in notifs if _action_has_highlight(notif["actions"])
-            ])
-
-        current_state = yield self.get_state_at(room_id, now_token)
-
-        current_state = {
-            (e.type, e.state_key): e
-            for e in sync_config.filter_collection.filter_room_state(
-                current_state.values()
-            )
-        }
-
-        account_data = self.account_data_for_room(
-            room_id, tags_by_room, account_data_by_room
-        )
-
-        account_data = sync_config.filter_collection.filter_room_account_data(
-            account_data
+        room_sync = yield self.incremental_sync_with_gap_for_room(
+            room_id, sync_config,
+            now_token=now_token,
+            since_token=timeline_since_token,
+            ephemeral_by_room=ephemeral_by_room,
+            tags_by_room=tags_by_room,
+            account_data_by_room=account_data_by_room,
+            all_ephemeral_by_room=ephemeral_by_room,
+            batch=batch,
+            full_state=True,
         )
 
-        ephemeral = sync_config.filter_collection.filter_room_ephemeral(
-            ephemeral_by_room.get(room_id, [])
-        )
-
-        defer.returnValue(JoinedSyncResult(
-            room_id=room_id,
-            timeline=batch,
-            state=current_state,
-            ephemeral=ephemeral,
-            account_data=account_data,
-            unread_notifications=unread_notifications,
-        ))
+        defer.returnValue(room_sync)
 
     def account_data_for_user(self, account_data):
         account_data_events = []
@@ -429,44 +402,20 @@ class SyncHandler(BaseHandler):
 
         defer.returnValue((now_token, ephemeral_by_room))
 
-    @defer.inlineCallbacks
     def full_state_sync_for_archived_room(self, room_id, sync_config,
                                           leave_event_id, leave_token,
                                           timeline_since_token, tags_by_room,
                                           account_data_by_room):
         """Sync a room for a client which is starting without any state
         Returns:
-            A Deferred JoinedSyncResult.
+            A Deferred ArchivedSyncResult.
         """
 
-        batch = yield self.load_filtered_recents(
-            room_id, sync_config, leave_token, since_token=timeline_since_token
-        )
-
-        leave_state = yield self.store.get_state_for_event(leave_event_id)
-
-        leave_state = {
-            (e.type, e.state_key): e
-            for e in sync_config.filter_collection.filter_room_state(
-                leave_state.values()
-            )
-        }
-
-        account_data = self.account_data_for_room(
-            room_id, tags_by_room, account_data_by_room
-        )
-
-        account_data = sync_config.filter_collection.filter_room_account_data(
-            account_data
+        return self.incremental_sync_for_archived_room(
+            sync_config, room_id, leave_event_id, timeline_since_token, tags_by_room,
+            account_data_by_room, full_state=True, leave_token=leave_token,
         )
 
-        defer.returnValue(ArchivedSyncResult(
-            room_id=room_id,
-            timeline=batch,
-            state=leave_state,
-            account_data=account_data,
-        ))
-
     @defer.inlineCallbacks
     def incremental_sync_with_gap(self, sync_config, since_token):
         """ Get the incremental delta needed to bring the client up to
@@ -512,154 +461,127 @@ class SyncHandler(BaseHandler):
                 sync_config.user
             )
 
-        timeline_limit = sync_config.filter_collection.timeline_limit()
+        user_id = sync_config.user.to_string()
 
-        room_events, _ = yield self.store.get_room_events_stream(
-            sync_config.user.to_string(),
-            from_key=since_token.room_key,
-            to_key=now_token.room_key,
-            limit=timeline_limit + 1,
-        )
+        timeline_limit = sync_config.filter_collection.timeline_limit()
 
         tags_by_room = yield self.store.get_updated_tags(
-            sync_config.user.to_string(),
+            user_id,
             since_token.account_data_key,
         )
 
         account_data, account_data_by_room = (
             yield self.store.get_updated_account_data_for_user(
-                sync_config.user.to_string(),
+                user_id,
                 since_token.account_data_key,
             )
         )
 
-        joined = []
-        archived = []
-        if len(room_events) <= timeline_limit:
-            # There is no gap in any of the rooms. Therefore we can just
-            # partition the new events by room and return them.
-            logger.debug("Got %i events for incremental sync - not limited",
-                         len(room_events))
-
-            invite_events = []
-            leave_events = []
-            events_by_room_id = {}
-            for event in room_events:
-                events_by_room_id.setdefault(event.room_id, []).append(event)
-                if event.room_id not in joined_room_ids:
-                    if (event.type == EventTypes.Member
-                            and event.state_key == sync_config.user.to_string()):
-                        if event.membership == Membership.INVITE:
-                            invite_events.append(event)
-                        elif event.membership in (Membership.LEAVE, Membership.BAN):
-                            leave_events.append(event)
-
-            for room_id in joined_room_ids:
-                recents = events_by_room_id.get(room_id, [])
-                logger.debug("Events for room %s: %r", room_id, recents)
-                state = {
-                    (event.type, event.state_key): event
-                    for event in recents if event.is_state()}
-                limited = False
+        # Get a list of membership change events that have happened.
+        rooms_changed = yield self.store.get_room_changes_for_user(
+            user_id, since_token.room_key, now_token.room_key
+        )
 
-                if recents:
-                    prev_batch = now_token.copy_and_replace(
-                        "room_key", recents[0].internal_metadata.before
-                    )
-                else:
-                    prev_batch = now_token
-
-                just_joined = yield self.check_joined_room(sync_config, state)
-                if just_joined:
-                    logger.debug("User has just joined %s: needs full state",
-                                 room_id)
-                    state = yield self.get_state_at(room_id, now_token)
-                    # the timeline is inherently limited if we've just joined
-                    limited = True
-
-                recents = sync_config.filter_collection.filter_room_timeline(recents)
-
-                state = {
-                    (e.type, e.state_key): e
-                    for e in sync_config.filter_collection.filter_room_state(
-                        state.values()
-                    )
-                }
-
-                acc_data = self.account_data_for_room(
-                    room_id, tags_by_room, account_data_by_room
-                )
+        mem_change_events_by_room_id = {}
+        for event in rooms_changed:
+            mem_change_events_by_room_id.setdefault(event.room_id, []).append(event)
 
-                acc_data = sync_config.filter_collection.filter_room_account_data(
-                    acc_data
-                )
-
-                ephemeral = sync_config.filter_collection.filter_room_ephemeral(
-                    ephemeral_by_room.get(room_id, [])
-                )
+        newly_joined_rooms = []
+        archived = []
+        invited = []
+        for room_id, events in mem_change_events_by_room_id.items():
+            non_joins = [e for e in events if e.membership != Membership.JOIN]
+            has_join = len(non_joins) != len(events)
+
+            # We want to figure out if we joined the room at some point since
+            # the last sync (even if we have since left). This is to make sure
+            # we do send down the room, and with full state, where necessary
+            if room_id in joined_room_ids or has_join:
+                old_state = yield self.get_state_at(room_id, since_token)
+                old_mem_ev = old_state.get((EventTypes.Member, user_id), None)
+                if not old_mem_ev or old_mem_ev.membership != Membership.JOIN:
+                        newly_joined_rooms.append(room_id)
+
+                if room_id in joined_room_ids:
+                    continue
+
+            if not non_joins:
+                continue
 
-                room_sync = JoinedSyncResult(
-                    room_id=room_id,
-                    timeline=TimelineBatch(
-                        events=recents,
-                        prev_batch=prev_batch,
-                        limited=limited,
-                    ),
-                    state=state,
-                    ephemeral=ephemeral,
-                    account_data=acc_data,
-                    unread_notifications={},
+            # Only bother if we're still currently invited
+            should_invite = non_joins[-1].membership == Membership.INVITE
+            if should_invite:
+                room_sync = InvitedSyncResult(room_id, invite=non_joins[-1])
+                if room_sync:
+                    invited.append(room_sync)
+
+            # Always include leave/ban events. Just take the last one.
+            # TODO: How do we handle ban -> leave in same batch?
+            leave_events = [
+                e for e in non_joins
+                if e.membership in (Membership.LEAVE, Membership.BAN)
+            ]
+
+            if leave_events:
+                leave_event = leave_events[-1]
+                room_sync = yield self.incremental_sync_for_archived_room(
+                    sync_config, room_id, leave_event.event_id, since_token,
+                    tags_by_room, account_data_by_room,
+                    full_state=room_id in newly_joined_rooms
                 )
-                logger.debug("Result for room %s: %r", room_id, room_sync)
-
                 if room_sync:
-                    notifs = yield self.unread_notifs_for_room_id(
-                        room_id, sync_config, all_ephemeral_by_room
-                    )
+                    archived.append(room_sync)
 
-                    if notifs is not None:
-                        notif_dict = room_sync.unread_notifications
-                        notif_dict["notification_count"] = len(notifs)
-                        notif_dict["highlight_count"] = len([
-                            1 for notif in notifs
-                            if _action_has_highlight(notif["actions"])
-                        ])
+        # Get all events for rooms we're currently joined to.
+        room_to_events = yield self.store.get_room_events_stream_for_rooms(
+            room_ids=joined_room_ids,
+            from_key=since_token.room_key,
+            to_key=now_token.room_key,
+            limit=timeline_limit + 1,
+        )
 
-                    joined.append(room_sync)
+        joined = []
+        # We loop through all room ids, even if there are no new events, in case
+        # there are non room events taht we need to notify about.
+        for room_id in joined_room_ids:
+            room_entry = room_to_events.get(room_id, None)
 
-        else:
-            logger.debug("Got %i events for incremental sync - hit limit",
-                         len(room_events))
+            if room_entry:
+                events, start_key = room_entry
 
-            invite_events = yield self.store.get_invites_for_user(
-                sync_config.user.to_string()
-            )
+                prev_batch_token = now_token.copy_and_replace("room_key", start_key)
 
-            leave_events = yield self.store.get_leave_and_ban_events_for_user(
-                sync_config.user.to_string()
-            )
+                newly_joined_room = room_id in newly_joined_rooms
+                full_state = newly_joined_room
 
-            for room_id in joined_room_ids:
-                room_sync = yield self.incremental_sync_with_gap_for_room(
-                    room_id, sync_config, since_token, now_token,
-                    ephemeral_by_room, tags_by_room, account_data_by_room,
-                    all_ephemeral_by_room=all_ephemeral_by_room,
+                batch = yield self.load_filtered_recents(
+                    room_id, sync_config, prev_batch_token,
+                    since_token=since_token,
+                    recents=events,
+                    newly_joined_room=newly_joined_room,
                 )
-                if room_sync:
-                    joined.append(room_sync)
+            else:
+                batch = TimelineBatch(
+                    events=[],
+                    prev_batch=since_token,
+                    limited=False,
+                )
+                full_state = False
 
-        for leave_event in leave_events:
-            room_sync = yield self.incremental_sync_for_archived_room(
-                sync_config, leave_event, since_token, tags_by_room,
-                account_data_by_room
+            room_sync = yield self.incremental_sync_with_gap_for_room(
+                room_id=room_id,
+                sync_config=sync_config,
+                since_token=since_token,
+                now_token=now_token,
+                ephemeral_by_room=ephemeral_by_room,
+                tags_by_room=tags_by_room,
+                account_data_by_room=account_data_by_room,
+                all_ephemeral_by_room=all_ephemeral_by_room,
+                batch=batch,
+                full_state=full_state,
             )
             if room_sync:
-                archived.append(room_sync)
-
-        invited = [
-            InvitedSyncResult(room_id=event.room_id, invite=event)
-            for event in invite_events
-        ]
+                joined.append(room_sync)
 
         account_data_for_user = sync_config.filter_collection.filter_account_data(
             self.account_data_for_user(account_data)
@@ -680,28 +602,40 @@ class SyncHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def load_filtered_recents(self, room_id, sync_config, now_token,
-                              since_token=None):
+                              since_token=None, recents=None, newly_joined_room=False):
         """
         :returns a Deferred TimelineBatch
         """
-        limited = True
-        recents = []
         filtering_factor = 2
         timeline_limit = sync_config.filter_collection.timeline_limit()
-        load_limit = max(timeline_limit * filtering_factor, 100)
-        max_repeat = 3  # Only try a few times per room, otherwise
+        load_limit = max(timeline_limit * filtering_factor, 10)
+        max_repeat = 5  # Only try a few times per room, otherwise
         room_key = now_token.room_key
         end_key = room_key
 
+        limited = recents is None or newly_joined_room or timeline_limit < len(recents)
+
+        if recents is not None:
+            recents = sync_config.filter_collection.filter_room_timeline(recents)
+            recents = yield self._filter_events_for_client(
+                sync_config.user.to_string(),
+                recents,
+                is_peeking=sync_config.is_guest,
+            )
+        else:
+            recents = []
+
+        since_key = None
+        if since_token and not newly_joined_room:
+            since_key = since_token.room_key
+
         while limited and len(recents) < timeline_limit and max_repeat:
-            events, keys = yield self.store.get_recent_events_for_room(
+            events, end_key = yield self.store.get_room_events_stream_for_room(
                 room_id,
                 limit=load_limit + 1,
-                from_token=since_token.room_key if since_token else None,
-                end_token=end_key,
+                from_key=since_key,
+                to_key=end_key,
             )
-            room_key, _ = keys
-            end_key = "s" + room_key.split('-')[-1]
             loaded_recents = sync_config.filter_collection.filter_room_timeline(events)
             loaded_recents = yield self._filter_events_for_client(
                 sync_config.user.to_string(),
@@ -710,8 +644,10 @@ class SyncHandler(BaseHandler):
             )
             loaded_recents.extend(recents)
             recents = loaded_recents
+
             if len(events) <= load_limit:
                 limited = False
+                break
             max_repeat -= 1
 
         if len(recents) > timeline_limit:
@@ -724,7 +660,9 @@ class SyncHandler(BaseHandler):
         )
 
         defer.returnValue(TimelineBatch(
-            events=recents, prev_batch=prev_batch_token, limited=limited
+            events=recents,
+            prev_batch=prev_batch_token,
+            limited=limited or newly_joined_room
         ))
 
     @defer.inlineCallbacks
@@ -732,25 +670,12 @@ class SyncHandler(BaseHandler):
                                            since_token, now_token,
                                            ephemeral_by_room, tags_by_room,
                                            account_data_by_room,
-                                           all_ephemeral_by_room):
-        """ Get the incremental delta needed to bring the client up to date for
-        the room. Gives the client the most recent events and the changes to
-        state.
-        Returns:
-            A Deferred JoinedSyncResult
-        """
-        logger.debug("Doing incremental sync for room %s between %s and %s",
-                     room_id, since_token, now_token)
-
-        # TODO(mjark): Check for redactions we might have missed.
-
-        batch = yield self.load_filtered_recents(
-            room_id, sync_config, now_token, since_token,
-        )
-
-        logger.debug("Recents %r", batch)
+                                           all_ephemeral_by_room,
+                                           batch, full_state=False):
+        if full_state:
+            state = yield self.get_state_at(room_id, now_token)
 
-        if batch.limited:
+        elif batch.limited:
             current_state = yield self.get_state_at(room_id, now_token)
 
             state_at_previous_sync = yield self.get_state_at(
@@ -814,43 +739,48 @@ class SyncHandler(BaseHandler):
         defer.returnValue(room_sync)
 
     @defer.inlineCallbacks
-    def incremental_sync_for_archived_room(self, sync_config, leave_event,
+    def incremental_sync_for_archived_room(self, sync_config, room_id, leave_event_id,
                                            since_token, tags_by_room,
-                                           account_data_by_room):
+                                           account_data_by_room, full_state,
+                                           leave_token=None):
         """ Get the incremental delta needed to bring the client up to date for
         the archived room.
         Returns:
             A Deferred ArchivedSyncResult
         """
 
-        stream_token = yield self.store.get_stream_token_for_event(
-            leave_event.event_id
-        )
+        if not leave_token:
+            stream_token = yield self.store.get_stream_token_for_event(
+                leave_event_id
+            )
 
-        leave_token = since_token.copy_and_replace("room_key", stream_token)
+            leave_token = since_token.copy_and_replace("room_key", stream_token)
 
-        if since_token.is_after(leave_token):
+        if since_token and since_token.is_after(leave_token):
             defer.returnValue(None)
 
         batch = yield self.load_filtered_recents(
-            leave_event.room_id, sync_config, leave_token, since_token,
+            room_id, sync_config, leave_token, since_token,
         )
 
         logger.debug("Recents %r", batch)
 
         state_events_at_leave = yield self.store.get_state_for_event(
-            leave_event.event_id
+            leave_event_id
         )
 
-        state_at_previous_sync = yield self.get_state_at(
-            leave_event.room_id, stream_position=since_token
-        )
+        if not full_state:
+            state_at_previous_sync = yield self.get_state_at(
+                room_id, stream_position=since_token
+            )
 
-        state_events_delta = yield self.compute_state_delta(
-            since_token=since_token,
-            previous_state=state_at_previous_sync,
-            current_state=state_events_at_leave,
-        )
+            state_events_delta = yield self.compute_state_delta(
+                since_token=since_token,
+                previous_state=state_at_previous_sync,
+                current_state=state_events_at_leave,
+            )
+        else:
+            state_events_delta = state_events_at_leave
 
         state_events_delta = {
             (e.type, e.state_key): e
@@ -860,7 +790,7 @@ class SyncHandler(BaseHandler):
         }
 
         account_data = self.account_data_for_room(
-            leave_event.room_id, tags_by_room, account_data_by_room
+            room_id, tags_by_room, account_data_by_room
         )
 
         account_data = sync_config.filter_collection.filter_room_account_data(
@@ -868,7 +798,7 @@ class SyncHandler(BaseHandler):
         )
 
         room_sync = ArchivedSyncResult(
-            room_id=leave_event.room_id,
+            room_id=room_id,
             timeline=batch,
             state=state_events_delta,
             account_data=account_data,
diff --git a/synapse/storage/account_data.py b/synapse/storage/account_data.py
index 9c6597e012..822c8bbe00 100644
--- a/synapse/storage/account_data.py
+++ b/synapse/storage/account_data.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 from ._base import SQLBaseStore
+from synapse.util.caches.stream_change_cache import StreamChangeCache
 from twisted.internet import defer
 
 import ujson as json
@@ -23,6 +24,14 @@ logger = logging.getLogger(__name__)
 
 
 class AccountDataStore(SQLBaseStore):
+    def __init__(self, hs):
+        super(AccountDataStore, self).__init__(hs)
+
+        self._account_data_stream_cache = StreamChangeCache(
+            "AccountDataAndTagsChangeCache",
+            self._account_data_id_gen.get_max_token(None),
+            max_size=1000,
+        )
 
     def get_account_data_for_user(self, user_id):
         """Get all the client account_data for a user.
@@ -83,7 +92,7 @@ class AccountDataStore(SQLBaseStore):
             "get_account_data_for_room", get_account_data_for_room_txn
         )
 
-    def get_updated_account_data_for_user(self, user_id, stream_id):
+    def get_updated_account_data_for_user(self, user_id, stream_id, room_ids=None):
         """Get all the client account_data for a that's changed.
 
         Args:
@@ -120,6 +129,12 @@ class AccountDataStore(SQLBaseStore):
 
             return (global_account_data, account_data_by_room)
 
+        changed = self._account_data_stream_cache.has_entity_changed(
+            user_id, int(stream_id)
+        )
+        if not changed:
+            return ({}, {})
+
         return self.runInteraction(
             "get_updated_account_data_for_user", get_updated_account_data_for_user_txn
         )
@@ -186,6 +201,10 @@ class AccountDataStore(SQLBaseStore):
                     "content": content_json,
                 }
             )
+            txn.call_after(
+                self._account_data_stream_cache.entity_has_changed,
+                user_id, next_id,
+            )
             self._update_max_stream_id(txn, next_id)
 
         with (yield self._account_data_id_gen.get_next(self)) as next_id:
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 298cb9bada..5e85552029 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -210,6 +210,12 @@ class EventsStore(SQLBaseStore):
         for event, _ in events_and_contexts:
             txn.call_after(self._invalidate_get_event_cache, event.event_id)
 
+            if not backfilled:
+                txn.call_after(
+                    self._events_stream_cache.entity_has_changed,
+                    event.room_id, event.internal_metadata.stream_ordering,
+                )
+
         depth_updates = {}
         for event, _ in events_and_contexts:
             if event.internal_metadata.is_outlier():
diff --git a/synapse/storage/receipts.py b/synapse/storage/receipts.py
index c0593e23ee..8068c73740 100644
--- a/synapse/storage/receipts.py
+++ b/synapse/storage/receipts.py
@@ -15,11 +15,10 @@
 
 from ._base import SQLBaseStore
 from synapse.util.caches.descriptors import cachedInlineCallbacks, cachedList, cached
-from synapse.util.caches import cache_counter, caches_by_name
+from synapse.util.caches.stream_change_cache import StreamChangeCache
 
 from twisted.internet import defer
 
-from blist import sorteddict
 import logging
 import ujson as json
 
@@ -31,8 +30,8 @@ class ReceiptsStore(SQLBaseStore):
     def __init__(self, hs):
         super(ReceiptsStore, self).__init__(hs)
 
-        self._receipts_stream_cache = _RoomStreamChangeCache(
-            self._receipts_id_gen.get_max_token(None)
+        self._receipts_stream_cache = StreamChangeCache(
+            "ReceiptsRoomChangeCache", self._receipts_id_gen.get_max_token(None)
         )
 
     @cached(num_args=2)
@@ -78,8 +77,8 @@ class ReceiptsStore(SQLBaseStore):
         room_ids = set(room_ids)
 
         if from_key:
-            room_ids = yield self._receipts_stream_cache.get_rooms_changed(
-                self, room_ids, from_key
+            room_ids = yield self._receipts_stream_cache.get_entities_changed(
+                room_ids, from_key
             )
 
         results = yield self._get_linearized_receipts_for_rooms(
@@ -222,6 +221,11 @@ class ReceiptsStore(SQLBaseStore):
         # FIXME: This shouldn't invalidate the whole cache
         txn.call_after(self.get_linearized_receipts_for_room.invalidate_all)
 
+        txn.call_after(
+            self._receipts_stream_cache.entity_has_changed,
+            room_id, stream_id
+        )
+
         # We don't want to clobber receipts for more recent events, so we
         # have to compare orderings of existing receipts
         sql = (
@@ -309,9 +313,6 @@ class ReceiptsStore(SQLBaseStore):
 
         stream_id_manager = yield self._receipts_id_gen.get_next(self)
         with stream_id_manager as stream_id:
-            yield self._receipts_stream_cache.room_has_changed(
-                self, room_id, stream_id
-            )
             have_persisted = yield self.runInteraction(
                 "insert_linearized_receipt",
                 self.insert_linearized_receipt_txn,
@@ -370,63 +371,3 @@ class ReceiptsStore(SQLBaseStore):
                 "data": json.dumps(data),
             }
         )
-
-
-class _RoomStreamChangeCache(object):
-    """Keeps track of the stream_id of the latest change in rooms.
-
-    Given a list of rooms and stream key, it will give a subset of rooms that
-    may have changed since that key. If the key is too old then the cache
-    will simply return all rooms.
-    """
-    def __init__(self, current_key, size_of_cache=10000):
-        self._size_of_cache = size_of_cache
-        self._room_to_key = {}
-        self._cache = sorteddict()
-        self._earliest_key = current_key
-        self.name = "ReceiptsRoomChangeCache"
-        caches_by_name[self.name] = self._cache
-
-    @defer.inlineCallbacks
-    def get_rooms_changed(self, store, room_ids, key):
-        """Returns subset of room ids that have had new receipts since the
-        given key. If the key is too old it will just return the given list.
-        """
-        if key > (yield self._get_earliest_key(store)):
-            keys = self._cache.keys()
-            i = keys.bisect_right(key)
-
-            result = set(
-                self._cache[k] for k in keys[i:]
-            ).intersection(room_ids)
-
-            cache_counter.inc_hits(self.name)
-        else:
-            result = room_ids
-            cache_counter.inc_misses(self.name)
-
-        defer.returnValue(result)
-
-    @defer.inlineCallbacks
-    def room_has_changed(self, store, room_id, key):
-        """Informs the cache that the room has been changed at the given key.
-        """
-        if key > (yield self._get_earliest_key(store)):
-            old_key = self._room_to_key.get(room_id, None)
-            if old_key:
-                key = max(key, old_key)
-                self._cache.pop(old_key, None)
-            self._cache[key] = room_id
-
-            while len(self._cache) > self._size_of_cache:
-                k, r = self._cache.popitem()
-                self._earliest_key = max(k, self._earliest_key)
-                self._room_to_key.pop(r, None)
-
-    @defer.inlineCallbacks
-    def _get_earliest_key(self, store):
-        if self._earliest_key is None:
-            self._earliest_key = yield store.get_max_receipt_stream_id()
-            self._earliest_key = int(self._earliest_key)
-
-        defer.returnValue(self._earliest_key)
diff --git a/synapse/storage/schema/delta/28/events_room_stream.sql b/synapse/storage/schema/delta/28/events_room_stream.sql
new file mode 100644
index 0000000000..200c35e6e2
--- /dev/null
+++ b/synapse/storage/schema/delta/28/events_room_stream.sql
@@ -0,0 +1,16 @@
+/* Copyright 2016 OpenMarket Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+*/
+
+CREATE INDEX events_room_stream on events(room_id, stream_ordering);
diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py
index e31bad258a..6e81d46c60 100644
--- a/synapse/storage/stream.py
+++ b/synapse/storage/stream.py
@@ -37,6 +37,7 @@ from twisted.internet import defer
 
 from ._base import SQLBaseStore
 from synapse.util.caches.descriptors import cachedInlineCallbacks
+from synapse.util.caches.stream_change_cache import StreamChangeCache
 from synapse.api.constants import EventTypes
 from synapse.types import RoomStreamToken
 from synapse.util.logutils import log_function
@@ -77,6 +78,12 @@ def upper_bound(token):
 
 
 class StreamStore(SQLBaseStore):
+    def __init__(self, hs):
+        super(StreamStore, self).__init__(hs)
+
+        self._events_stream_cache = StreamChangeCache(
+            "EventsRoomStreamChangeCache", self._stream_id_gen.get_max_token(None)
+        )
 
     @defer.inlineCallbacks
     def get_appservice_room_stream(self, service, from_key, to_key, limit=0):
@@ -157,6 +164,135 @@ class StreamStore(SQLBaseStore):
         results = yield self.runInteraction("get_appservice_room_stream", f)
         defer.returnValue(results)
 
+    @defer.inlineCallbacks
+    def get_room_events_stream_for_rooms(self, room_ids, from_key, to_key, limit=0):
+        from_id = RoomStreamToken.parse_stream_token(from_key).stream
+
+        room_ids = yield self._events_stream_cache.get_entities_changed(
+            room_ids, from_id
+        )
+
+        if not room_ids:
+            defer.returnValue({})
+
+        results = {}
+        room_ids = list(room_ids)
+        for rm_ids in (room_ids[i:i+20] for i in xrange(0, len(room_ids), 20)):
+            res = yield defer.gatherResults([
+                self.get_room_events_stream_for_room(
+                    room_id, from_key, to_key, limit
+                ).addCallback(lambda r, rm: (rm, r), room_id)
+                for room_id in room_ids
+            ])
+            results.update(dict(res))
+
+        defer.returnValue(results)
+
+    @defer.inlineCallbacks
+    def get_room_events_stream_for_room(self, room_id, from_key, to_key, limit=0):
+        if from_key is not None:
+            from_id = RoomStreamToken.parse_stream_token(from_key).stream
+        else:
+            from_id = None
+        to_id = RoomStreamToken.parse_stream_token(to_key).stream
+
+        if from_key == to_key:
+            defer.returnValue(([], from_key))
+
+        if from_id:
+            has_changed = yield self._events_stream_cache.has_entity_changed(
+                room_id, from_id
+            )
+
+            if not has_changed:
+                defer.returnValue(([], from_key))
+
+        def f(txn):
+            if from_id is not None:
+                sql = (
+                    "SELECT event_id, stream_ordering FROM events WHERE"
+                    " room_id = ?"
+                    " AND not outlier"
+                    " AND stream_ordering > ? AND stream_ordering <= ?"
+                    " ORDER BY stream_ordering DESC LIMIT ?"
+                )
+                txn.execute(sql, (room_id, from_id, to_id, limit))
+            else:
+                sql = (
+                    "SELECT event_id, stream_ordering FROM events WHERE"
+                    " room_id = ?"
+                    " AND not outlier"
+                    " AND stream_ordering <= ?"
+                    " ORDER BY stream_ordering DESC LIMIT ?"
+                )
+                txn.execute(sql, (room_id, to_id, limit))
+
+            rows = self.cursor_to_dict(txn)
+
+            ret = self._get_events_txn(
+                txn,
+                [r["event_id"] for r in rows],
+                get_prev_content=True
+            )
+
+            self._set_before_and_after(ret, rows, topo_order=False)
+
+            ret.reverse()
+
+            if rows:
+                key = "s%d" % min(r["stream_ordering"] for r in rows)
+            else:
+                # Assume we didn't get anything because there was nothing to
+                # get.
+                key = from_key
+
+            return ret, key
+        res = yield self.runInteraction("get_room_events_stream_for_room", f)
+        defer.returnValue(res)
+
+    def get_room_changes_for_user(self, user_id, from_key, to_key):
+        if from_key is not None:
+            from_id = RoomStreamToken.parse_stream_token(from_key).stream
+        else:
+            from_id = None
+        to_id = RoomStreamToken.parse_stream_token(to_key).stream
+
+        if from_key == to_key:
+            return defer.succeed([])
+
+        def f(txn):
+            if from_id is not None:
+                sql = (
+                    "SELECT m.event_id, stream_ordering FROM events AS e,"
+                    " room_memberships AS m"
+                    " WHERE e.event_id = m.event_id"
+                    " AND m.user_id = ?"
+                    " AND e.stream_ordering > ? AND e.stream_ordering <= ?"
+                    " ORDER BY e.stream_ordering ASC"
+                )
+                txn.execute(sql, (user_id, from_id, to_id,))
+            else:
+                sql = (
+                    "SELECT m.event_id, stream_ordering FROM events AS e,"
+                    " room_memberships AS m"
+                    " WHERE e.event_id = m.event_id"
+                    " AND m.user_id = ?"
+                    " AND stream_ordering <= ?"
+                    " ORDER BY stream_ordering ASC"
+                )
+                txn.execute(sql, (user_id, to_id,))
+            rows = self.cursor_to_dict(txn)
+
+            ret = self._get_events_txn(
+                txn,
+                [r["event_id"] for r in rows],
+                get_prev_content=True
+            )
+
+            return ret
+
+        return self.runInteraction("get_room_changes_for_user", f)
+
     @log_function
     def get_room_events_stream(
         self,
@@ -174,7 +310,8 @@ class StreamStore(SQLBaseStore):
                 "SELECT c.room_id FROM history_visibility AS h"
                 " INNER JOIN current_state_events AS c"
                 " ON h.event_id = c.event_id"
-                " WHERE c.room_id IN (%s) AND h.history_visibility = 'world_readable'" % (
+                " WHERE c.room_id IN (%s)"
+                " AND h.history_visibility = 'world_readable'" % (
                     ",".join(map(lambda _: "?", room_ids))
                 )
             )
@@ -434,6 +571,18 @@ class StreamStore(SQLBaseStore):
             row["topological_ordering"], row["stream_ordering"],)
         )
 
+    def get_max_topological_token_for_stream_and_room(self, room_id, stream_key):
+        sql = (
+            "SELECT max(topological_ordering) FROM events"
+            " WHERE room_id = ? AND stream_ordering < ?"
+        )
+        return self._execute(
+            "get_max_topological_token_for_stream_and_room", None,
+            sql, room_id, stream_key,
+        ).addCallback(
+            lambda r: r[0][0] if r else 0
+        )
+
     def _get_max_topological_txn(self, txn):
         txn.execute(
             "SELECT MAX(topological_ordering) FROM events"
@@ -445,10 +594,13 @@ class StreamStore(SQLBaseStore):
         return rows[0][0] if rows else 0
 
     @staticmethod
-    def _set_before_and_after(events, rows):
+    def _set_before_and_after(events, rows, topo_order=True):
         for event, row in zip(events, rows):
             stream = row["stream_ordering"]
-            topo = event.depth
+            if topo_order:
+                topo = event.depth
+            else:
+                topo = None
             internal = event.internal_metadata
             internal.before = str(RoomStreamToken(topo, stream - 1))
             internal.after = str(RoomStreamToken(topo, stream))
diff --git a/synapse/storage/tags.py b/synapse/storage/tags.py
index 4c39e07cbd..e1a9c0c261 100644
--- a/synapse/storage/tags.py
+++ b/synapse/storage/tags.py
@@ -24,7 +24,6 @@ logger = logging.getLogger(__name__)
 
 
 class TagsStore(SQLBaseStore):
-
     def get_max_account_data_stream_id(self):
         """Get the current max stream id for the private user data stream
 
@@ -80,6 +79,12 @@ class TagsStore(SQLBaseStore):
             room_ids = [row[0] for row in txn.fetchall()]
             return room_ids
 
+        changed = self._account_data_stream_cache.has_entity_changed(
+            user_id, int(stream_id)
+        )
+        if not changed:
+            defer.returnValue({})
+
         room_ids = yield self.runInteraction(
             "get_updated_tags", get_updated_tags_txn
         )
@@ -177,6 +182,11 @@ class TagsStore(SQLBaseStore):
             next_id(int): The the revision to advance to.
         """
 
+        txn.call_after(
+            self._account_data_stream_cache.entity_has_changed,
+            user_id, next_id
+        )
+
         update_max_id_sql = (
             "UPDATE account_data_max_stream_id"
             " SET stream_id = ?"
diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py
new file mode 100644
index 0000000000..c673b1bdfc
--- /dev/null
+++ b/synapse/util/caches/stream_change_cache.py
@@ -0,0 +1,107 @@
+# -*- coding: utf-8 -*-
+# Copyright 2016 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.util.caches import cache_counter, caches_by_name
+
+
+from blist import sorteddict
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class StreamChangeCache(object):
+    """Keeps track of the stream positions of the latest change in a set of entities.
+
+    Typically the entity will be a room or user id.
+
+    Given a list of entities and a stream position, it will give a subset of
+    entities that may have changed since that position. If position key is too
+    old then the cache will simply return all given entities.
+    """
+    def __init__(self, name, current_stream_pos, max_size=10000):
+        self._max_size = max_size
+        self._entity_to_key = {}
+        self._cache = sorteddict()
+        self._earliest_known_stream_pos = current_stream_pos
+        self.name = name
+        caches_by_name[self.name] = self._cache
+
+    def has_entity_changed(self, entity, stream_pos):
+        """Returns True if the entity may have been updated since stream_pos
+        """
+        assert type(stream_pos) is int
+
+        if stream_pos < self._earliest_known_stream_pos:
+            cache_counter.inc_misses(self.name)
+            return True
+
+        if stream_pos == self._earliest_known_stream_pos:
+            # If the same as the earliest key, assume nothing has changed.
+            cache_counter.inc_hits(self.name)
+            return False
+
+        latest_entity_change_pos = self._entity_to_key.get(entity, None)
+        if latest_entity_change_pos is None:
+            cache_counter.inc_misses(self.name)
+            return True
+
+        if stream_pos < latest_entity_change_pos:
+            cache_counter.inc_misses(self.name)
+            return True
+
+        cache_counter.inc_hits(self.name)
+        return False
+
+    def get_entities_changed(self, entities, stream_pos):
+        """Returns subset of entities that have had new things since the
+        given position. If the position is too old it will just return the given list.
+        """
+        assert type(stream_pos) is int
+
+        if stream_pos >= self._earliest_known_stream_pos:
+            keys = self._cache.keys()
+            i = keys.bisect_right(stream_pos)
+
+            result = set(
+                self._cache[k] for k in keys[i:]
+            ).intersection(entities)
+
+            cache_counter.inc_hits(self.name)
+        else:
+            result = entities
+            cache_counter.inc_misses(self.name)
+
+        return result
+
+    def entity_has_changed(self, entity, stream_pos):
+        """Informs the cache that the entity has been changed at the given
+        position.
+        """
+        assert type(stream_pos) is int
+
+        if stream_pos > self._earliest_known_stream_pos:
+            old_pos = self._entity_to_key.get(entity, None)
+            if old_pos:
+                stream_pos = max(stream_pos, old_pos)
+                self._cache.pop(old_pos, None)
+            self._cache[stream_pos] = entity
+            self._entity_to_key[entity] = stream_pos
+
+            while len(self._cache) > self._max_size:
+                k, r = self._cache.popitem()
+                self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
+                self._entity_to_key.pop(r, None)
diff --git a/tests/rest/client/v1/test_rooms.py b/tests/rest/client/v1/test_rooms.py
index 2fe6f695f5..ad5dd3bd6e 100644
--- a/tests/rest/client/v1/test_rooms.py
+++ b/tests/rest/client/v1/test_rooms.py
@@ -1045,13 +1045,6 @@ class RoomMessageListTestCase(RestTestCase):
         self.assertTrue("end" in response)
 
     @defer.inlineCallbacks
-    def test_stream_token_is_rejected_for_back_pagination(self):
-        (code, response) = yield self.mock_resource.trigger_get(
-            "/rooms/%s/messages?access_token=x&from=s0_0_0_0_0&dir=b" %
-            self.room_id)
-        self.assertEquals(400, code)
-
-    @defer.inlineCallbacks
     def test_stream_token_is_accepted_for_fwd_pagianation(self):
         token = "s0_0_0_0_0"
         (code, response) = yield self.mock_resource.trigger_get(
@@ -1061,4 +1054,4 @@ class RoomMessageListTestCase(RestTestCase):
         self.assertTrue("start" in response)
         self.assertEquals(token, response['start'])
         self.assertTrue("chunk" in response)
-        self.assertTrue("end" in response)
\ No newline at end of file
+        self.assertTrue("end" in response)