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-rw-r--r--synapse/api/filtering.py9
-rwxr-xr-xsynapse/app/homeserver.py4
-rw-r--r--synapse/federation/transport/server.py4
-rw-r--r--synapse/groups/attestations.py2
-rw-r--r--synapse/handlers/profile.py2
-rw-r--r--synapse/handlers/room.py24
-rw-r--r--synapse/handlers/room_member.py4
-rw-r--r--synapse/handlers/search.py2
-rw-r--r--synapse/handlers/sync.py87
-rw-r--r--synapse/metrics/background_process_metrics.py10
-rw-r--r--synapse/rest/client/v1/room.py9
-rw-r--r--synapse/rest/media/v1/media_repository.py2
-rw-r--r--synapse/rest/media/v1/preview_url_resource.py2
-rw-r--r--synapse/secrets.py7
-rw-r--r--synapse/storage/client_ips.py2
-rw-r--r--synapse/storage/devices.py2
-rw-r--r--synapse/storage/event_federation.py15
-rw-r--r--synapse/storage/event_push_actions.py4
-rw-r--r--synapse/storage/events.py2
-rw-r--r--synapse/storage/schema/delta/50/make_event_content_nullable.py92
-rw-r--r--synapse/storage/schema/full_schemas/16/event_edges.sql3
-rw-r--r--synapse/storage/schema/full_schemas/16/im.sql7
-rw-r--r--synapse/storage/stream.py14
-rw-r--r--synapse/storage/transactions.py4
-rw-r--r--synapse/util/caches/expiringcache.py2
25 files changed, 251 insertions, 64 deletions
diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index 7e767b9bf5..186831e118 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -117,6 +117,9 @@ ROOM_EVENT_FILTER_SCHEMA = {
         "lazy_load_members": {
             "type": "boolean"
         },
+        "include_redundant_members": {
+            "type": "boolean"
+        },
     }
 }
 
@@ -267,6 +270,9 @@ class FilterCollection(object):
     def lazy_load_members(self):
         return self._room_state_filter.lazy_load_members()
 
+    def include_redundant_members(self):
+        return self._room_state_filter.include_redundant_members()
+
     def filter_presence(self, events):
         return self._presence_filter.filter(events)
 
@@ -426,6 +432,9 @@ class Filter(object):
     def lazy_load_members(self):
         return self.filter_json.get("lazy_load_members", False)
 
+    def include_redundant_members(self):
+        return self.filter_json.get("include_redundant_members", False)
+
 
 def _matches_wildcard(actual_value, filter_value):
     if filter_value.endswith("*"):
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index b7e7718290..57b815d777 100755
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -429,7 +429,7 @@ def run(hs):
     stats_process = []
 
     def start_phone_stats_home():
-        run_as_background_process("phone_stats_home", phone_stats_home)
+        return run_as_background_process("phone_stats_home", phone_stats_home)
 
     @defer.inlineCallbacks
     def phone_stats_home():
@@ -502,7 +502,7 @@ def run(hs):
             )
 
     def generate_user_daily_visit_stats():
-        run_as_background_process(
+        return run_as_background_process(
             "generate_user_daily_visits",
             hs.get_datastore().generate_user_daily_visits,
         )
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index c9beca27c2..8574898f0c 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -404,10 +404,10 @@ class FederationMakeLeaveServlet(BaseFederationServlet):
 
 
 class FederationSendLeaveServlet(BaseFederationServlet):
-    PATH = "/send_leave/(?P<room_id>[^/]*)/(?P<txid>[^/]*)"
+    PATH = "/send_leave/(?P<room_id>[^/]*)/(?P<event_id>[^/]*)"
 
     @defer.inlineCallbacks
-    def on_PUT(self, origin, content, query, room_id, txid):
+    def on_PUT(self, origin, content, query, room_id, event_id):
         content = yield self.handler.on_send_leave_request(origin, content)
         defer.returnValue((200, content))
 
diff --git a/synapse/groups/attestations.py b/synapse/groups/attestations.py
index 4216af0a27..b04f4234ca 100644
--- a/synapse/groups/attestations.py
+++ b/synapse/groups/attestations.py
@@ -153,7 +153,7 @@ class GroupAttestionRenewer(object):
         defer.returnValue({})
 
     def _start_renew_attestations(self):
-        run_as_background_process("renew_attestations", self._renew_attestations)
+        return run_as_background_process("renew_attestations", self._renew_attestations)
 
     @defer.inlineCallbacks
     def _renew_attestations(self):
diff --git a/synapse/handlers/profile.py b/synapse/handlers/profile.py
index 43692b83a8..cb5c6d587e 100644
--- a/synapse/handlers/profile.py
+++ b/synapse/handlers/profile.py
@@ -256,7 +256,7 @@ class ProfileHandler(BaseHandler):
                 )
 
     def _start_update_remote_profile_cache(self):
-        run_as_background_process(
+        return run_as_background_process(
             "Update remote profile", self._update_remote_profile_cache,
         )
 
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 003b848c00..7b7804d9b2 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -15,6 +15,7 @@
 # limitations under the License.
 
 """Contains functions for performing events on rooms."""
+import itertools
 import logging
 import math
 import string
@@ -401,7 +402,7 @@ class RoomContextHandler(object):
         self.store = hs.get_datastore()
 
     @defer.inlineCallbacks
-    def get_event_context(self, user, room_id, event_id, limit):
+    def get_event_context(self, user, room_id, event_id, limit, event_filter):
         """Retrieves events, pagination tokens and state around a given event
         in a room.
 
@@ -411,6 +412,8 @@ class RoomContextHandler(object):
             event_id (str)
             limit (int): The maximum number of events to return in total
                 (excluding state).
+            event_filter (Filter|None): the filter to apply to the events returned
+                (excluding the target event_id)
 
         Returns:
             dict, or None if the event isn't found
@@ -443,7 +446,7 @@ class RoomContextHandler(object):
             )
 
         results = yield self.store.get_events_around(
-            room_id, event_id, before_limit, after_limit
+            room_id, event_id, before_limit, after_limit, event_filter
         )
 
         results["events_before"] = yield filter_evts(results["events_before"])
@@ -455,8 +458,23 @@ class RoomContextHandler(object):
         else:
             last_event_id = event_id
 
+        types = None
+        filtered_types = None
+        if event_filter and event_filter.lazy_load_members():
+            members = set(ev.sender for ev in itertools.chain(
+                results["events_before"],
+                (results["event"],),
+                results["events_after"],
+            ))
+            filtered_types = [EventTypes.Member]
+            types = [(EventTypes.Member, member) for member in members]
+
+        # XXX: why do we return the state as of the last event rather than the
+        # first? Shouldn't we be consistent with /sync?
+        # https://github.com/matrix-org/matrix-doc/issues/687
+
         state = yield self.store.get_state_for_events(
-            [last_event_id], None
+            [last_event_id], types, filtered_types=filtered_types,
         )
         results["state"] = list(state[last_event_id].values())
 
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index a832d91809..0d4a3f4677 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -708,6 +708,10 @@ class RoomMemberHandler(object):
             inviter_display_name = member_event.content.get("displayname", "")
             inviter_avatar_url = member_event.content.get("avatar_url", "")
 
+        # if user has no display name, default to their MXID
+        if not inviter_display_name:
+            inviter_display_name = user.to_string()
+
         canonical_room_alias = ""
         canonical_alias_event = room_state.get((EventTypes.CanonicalAlias, ""))
         if canonical_alias_event:
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 69ae9731d5..c464adbd0b 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -287,7 +287,7 @@ class SearchHandler(BaseHandler):
             contexts = {}
             for event in allowed_events:
                 res = yield self.store.get_events_around(
-                    event.room_id, event.event_id, before_limit, after_limit
+                    event.room_id, event.event_id, before_limit, after_limit,
                 )
 
                 logger.info(
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 4ced3144c8..dff1f67dcb 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -26,6 +26,8 @@ from synapse.api.constants import EventTypes, Membership
 from synapse.push.clientformat import format_push_rules_for_user
 from synapse.types import RoomStreamToken
 from synapse.util.async import concurrently_execute
+from synapse.util.caches.expiringcache import ExpiringCache
+from synapse.util.caches.lrucache import LruCache
 from synapse.util.caches.response_cache import ResponseCache
 from synapse.util.logcontext import LoggingContext
 from synapse.util.metrics import Measure, measure_func
@@ -33,6 +35,14 @@ from synapse.visibility import filter_events_for_client
 
 logger = logging.getLogger(__name__)
 
+# Store the cache that tracks which lazy-loaded members have been sent to a given
+# client for no more than 30 minutes.
+LAZY_LOADED_MEMBERS_CACHE_MAX_AGE = 30 * 60 * 1000
+
+# Remember the last 100 members we sent to a client for the purposes of
+# avoiding redundantly sending the same lazy-loaded members to the client
+LAZY_LOADED_MEMBERS_CACHE_MAX_SIZE = 100
+
 
 SyncConfig = collections.namedtuple("SyncConfig", [
     "user",
@@ -182,6 +192,12 @@ class SyncHandler(object):
         self.response_cache = ResponseCache(hs, "sync")
         self.state = hs.get_state_handler()
 
+        # ExpiringCache((User, Device)) -> LruCache(state_key => event_id)
+        self.lazy_loaded_members_cache = ExpiringCache(
+            "lazy_loaded_members_cache", self.clock,
+            max_len=0, expiry_ms=LAZY_LOADED_MEMBERS_CACHE_MAX_AGE,
+        )
+
     def wait_for_sync_for_user(self, sync_config, since_token=None, timeout=0,
                                full_state=False):
         """Get the sync for a client if we have new data for it now. Otherwise
@@ -505,9 +521,13 @@ class SyncHandler(object):
         with Measure(self.clock, "compute_state_delta"):
 
             types = None
-            lazy_load_members = sync_config.filter_collection.lazy_load_members()
             filtered_types = None
 
+            lazy_load_members = sync_config.filter_collection.lazy_load_members()
+            include_redundant_members = (
+                sync_config.filter_collection.include_redundant_members()
+            )
+
             if lazy_load_members:
                 # We only request state for the members needed to display the
                 # timeline:
@@ -523,6 +543,11 @@ class SyncHandler(object):
                 # only apply the filtering to room members
                 filtered_types = [EventTypes.Member]
 
+            timeline_state = {
+                (event.type, event.state_key): event.event_id
+                for event in batch.events if event.is_state()
+            }
+
             if full_state:
                 if batch:
                     current_state_ids = yield self.store.get_state_ids_for_event(
@@ -543,11 +568,6 @@ class SyncHandler(object):
 
                     state_ids = current_state_ids
 
-                timeline_state = {
-                    (event.type, event.state_key): event.event_id
-                    for event in batch.events if event.is_state()
-                }
-
                 state_ids = _calculate_state(
                     timeline_contains=timeline_state,
                     timeline_start=state_ids,
@@ -571,21 +591,6 @@ class SyncHandler(object):
                     filtered_types=filtered_types,
                 )
 
-                timeline_state = {
-                    (event.type, event.state_key): event.event_id
-                    for event in batch.events if event.is_state()
-                }
-
-                # TODO: optionally filter out redundant membership events at this
-                # point, to stop repeatedly sending members in every /sync as if
-                # the client isn't tracking them.
-                # When implemented, this should filter using event_ids (not mxids).
-                # In practice, limited syncs are
-                # relatively rare so it's not a total disaster to send redundant
-                # members down at this point. Redundant members are ones which
-                # repeatedly get sent down /sync because we don't know if the client
-                # is caching them or not.
-
                 state_ids = _calculate_state(
                     timeline_contains=timeline_state,
                     timeline_start=state_at_timeline_start,
@@ -596,16 +601,48 @@ class SyncHandler(object):
             else:
                 state_ids = {}
                 if lazy_load_members:
-                    # TODO: filter out redundant members based on their mxids (not their
-                    # event_ids) at this point. We know we can do it based on mxid as this
-                    # is an non-gappy incremental sync.
-
                     if types:
                         state_ids = yield self.store.get_state_ids_for_event(
                             batch.events[0].event_id, types=types,
                             filtered_types=filtered_types,
                         )
 
+            if lazy_load_members and not include_redundant_members:
+                cache_key = (sync_config.user.to_string(), sync_config.device_id)
+                cache = self.lazy_loaded_members_cache.get(cache_key)
+                if cache is None:
+                    logger.debug("creating LruCache for %r", cache_key)
+                    cache = LruCache(LAZY_LOADED_MEMBERS_CACHE_MAX_SIZE)
+                    self.lazy_loaded_members_cache[cache_key] = cache
+                else:
+                    logger.debug("found LruCache for %r", cache_key)
+
+                # if it's a new sync sequence, then assume the client has had
+                # amnesia and doesn't want any recent lazy-loaded members
+                # de-duplicated.
+                if since_token is None:
+                    logger.debug("clearing LruCache for %r", cache_key)
+                    cache.clear()
+                else:
+                    # only send members which aren't in our LruCache (either
+                    # because they're new to this client or have been pushed out
+                    # of the cache)
+                    logger.debug("filtering state from %r...", state_ids)
+                    state_ids = {
+                        t: event_id
+                        for t, event_id in state_ids.iteritems()
+                        if cache.get(t[1]) != event_id
+                    }
+                    logger.debug("...to %r", state_ids)
+
+                # add any member IDs we are about to send into our LruCache
+                for t, event_id in itertools.chain(
+                    state_ids.items(),
+                    timeline_state.items(),
+                ):
+                    if t[0] == EventTypes.Member:
+                        cache.set(t[1], event_id)
+
         state = {}
         if state_ids:
             state = yield self.store.get_events(list(state_ids.values()))
diff --git a/synapse/metrics/background_process_metrics.py b/synapse/metrics/background_process_metrics.py
index 9d820e44a6..ce678d5f75 100644
--- a/synapse/metrics/background_process_metrics.py
+++ b/synapse/metrics/background_process_metrics.py
@@ -151,13 +151,19 @@ def run_as_background_process(desc, func, *args, **kwargs):
     This should be used to wrap processes which are fired off to run in the
     background, instead of being associated with a particular request.
 
+    It returns a Deferred which completes when the function completes, but it doesn't
+    follow the synapse logcontext rules, which makes it appropriate for passing to
+    clock.looping_call and friends (or for firing-and-forgetting in the middle of a
+    normal synapse inlineCallbacks function).
+
     Args:
         desc (str): a description for this background process type
         func: a function, which may return a Deferred
         args: positional args for func
         kwargs: keyword args for func
 
-    Returns: None
+    Returns: Deferred which returns the result of func, but note that it does not
+        follow the synapse logcontext rules.
     """
     @defer.inlineCallbacks
     def run():
@@ -176,4 +182,4 @@ def run_as_background_process(desc, func, *args, **kwargs):
                 _background_processes[desc].remove(proc)
 
     with PreserveLoggingContext():
-        run()
+        return run()
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index b7bd878c90..13c331550b 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -531,11 +531,20 @@ class RoomEventContextServlet(ClientV1RestServlet):
 
         limit = parse_integer(request, "limit", default=10)
 
+        # picking the API shape for symmetry with /messages
+        filter_bytes = parse_string(request, "filter")
+        if filter_bytes:
+            filter_json = urlparse.unquote(filter_bytes).decode("UTF-8")
+            event_filter = Filter(json.loads(filter_json))
+        else:
+            event_filter = None
+
         results = yield self.room_context_handler.get_event_context(
             requester.user,
             room_id,
             event_id,
             limit,
+            event_filter,
         )
 
         if not results:
diff --git a/synapse/rest/media/v1/media_repository.py b/synapse/rest/media/v1/media_repository.py
index 5b13378caa..174ad20123 100644
--- a/synapse/rest/media/v1/media_repository.py
+++ b/synapse/rest/media/v1/media_repository.py
@@ -106,7 +106,7 @@ class MediaRepository(object):
         )
 
     def _start_update_recently_accessed(self):
-        run_as_background_process(
+        return run_as_background_process(
             "update_recently_accessed_media", self._update_recently_accessed,
         )
 
diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index 4efd5339a4..27aa0def2f 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -373,7 +373,7 @@ class PreviewUrlResource(Resource):
         })
 
     def _start_expire_url_cache_data(self):
-        run_as_background_process(
+        return run_as_background_process(
             "expire_url_cache_data", self._expire_url_cache_data,
         )
 
diff --git a/synapse/secrets.py b/synapse/secrets.py
index f397daaa5e..f05e9ea535 100644
--- a/synapse/secrets.py
+++ b/synapse/secrets.py
@@ -20,17 +20,16 @@ See https://docs.python.org/3/library/secrets.html#module-secrets for the API
 used in Python 3.6, and the API emulated in Python 2.7.
 """
 
-import six
+import sys
 
-if six.PY3:
+# secrets is available since python 3.6
+if sys.version_info[0:2] >= (3, 6):
     import secrets
 
     def Secrets():
         return secrets
 
-
 else:
-
     import os
     import binascii
 
diff --git a/synapse/storage/client_ips.py b/synapse/storage/client_ips.py
index 77ae10da3d..b8cefd43d6 100644
--- a/synapse/storage/client_ips.py
+++ b/synapse/storage/client_ips.py
@@ -102,7 +102,7 @@ class ClientIpStore(background_updates.BackgroundUpdateStore):
                 to_update,
             )
 
-        run_as_background_process(
+        return run_as_background_process(
             "update_client_ips", update,
         )
 
diff --git a/synapse/storage/devices.py b/synapse/storage/devices.py
index 52dccb1507..c0943ecf91 100644
--- a/synapse/storage/devices.py
+++ b/synapse/storage/devices.py
@@ -712,7 +712,7 @@ class DeviceStore(SQLBaseStore):
 
             logger.info("Pruned %d device list outbound pokes", txn.rowcount)
 
-        run_as_background_process(
+        return run_as_background_process(
             "prune_old_outbound_device_pokes",
             self.runInteraction,
             "_prune_old_outbound_device_pokes",
diff --git a/synapse/storage/event_federation.py b/synapse/storage/event_federation.py
index 14500ee59c..8bd35df119 100644
--- a/synapse/storage/event_federation.py
+++ b/synapse/storage/event_federation.py
@@ -114,9 +114,9 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
         sql = (
             "SELECT b.event_id, MAX(e.depth) FROM events as e"
             " INNER JOIN event_edges as g"
-            " ON g.event_id = e.event_id AND g.room_id = e.room_id"
+            " ON g.event_id = e.event_id"
             " INNER JOIN event_backward_extremities as b"
-            " ON g.prev_event_id = b.event_id AND g.room_id = b.room_id"
+            " ON g.prev_event_id = b.event_id"
             " WHERE b.room_id = ? AND g.is_state is ?"
             " GROUP BY b.event_id"
         )
@@ -330,8 +330,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
             "SELECT depth, prev_event_id FROM event_edges"
             " INNER JOIN events"
             " ON prev_event_id = events.event_id"
-            " AND event_edges.room_id = events.room_id"
-            " WHERE event_edges.room_id = ? AND event_edges.event_id = ?"
+            " WHERE event_edges.event_id = ?"
             " AND event_edges.is_state = ?"
             " LIMIT ?"
         )
@@ -365,7 +364,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
 
             txn.execute(
                 query,
-                (room_id, event_id, False, limit - len(event_results))
+                (event_id, False, limit - len(event_results))
             )
 
             for row in txn:
@@ -402,7 +401,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
 
         query = (
             "SELECT prev_event_id FROM event_edges "
-            "WHERE room_id = ? AND event_id = ? AND is_state = ? "
+            "WHERE event_id = ? AND is_state = ? "
             "LIMIT ?"
         )
 
@@ -411,7 +410,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
             for event_id in front:
                 txn.execute(
                     query,
-                    (room_id, event_id, False, limit - len(event_results))
+                    (event_id, False, limit - len(event_results))
                 )
 
                 for e_id, in txn:
@@ -549,7 +548,7 @@ class EventFederationStore(EventFederationWorkerStore):
                 sql,
                 (self.stream_ordering_month_ago, self.stream_ordering_month_ago,)
             )
-        run_as_background_process(
+        return run_as_background_process(
             "delete_old_forward_extrem_cache",
             self.runInteraction,
             "_delete_old_forward_extrem_cache",
diff --git a/synapse/storage/event_push_actions.py b/synapse/storage/event_push_actions.py
index 4f44b0ad47..6840320641 100644
--- a/synapse/storage/event_push_actions.py
+++ b/synapse/storage/event_push_actions.py
@@ -460,7 +460,7 @@ class EventPushActionsWorkerStore(SQLBaseStore):
             )
 
     def _find_stream_orderings_for_times(self):
-        run_as_background_process(
+        return run_as_background_process(
             "event_push_action_stream_orderings",
             self.runInteraction,
             "_find_stream_orderings_for_times",
@@ -790,7 +790,7 @@ class EventPushActionsStore(EventPushActionsWorkerStore):
         """, (room_id, user_id, stream_ordering))
 
     def _start_rotate_notifs(self):
-        run_as_background_process("rotate_notifs", self._rotate_notifs)
+        return run_as_background_process("rotate_notifs", self._rotate_notifs)
 
     @defer.inlineCallbacks
     def _rotate_notifs(self):
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index a32a306495..c98e524ba1 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -524,7 +524,6 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
             iterable=list(new_latest_event_ids),
             retcols=["prev_event_id"],
             keyvalues={
-                "room_id": room_id,
                 "is_state": False,
             },
             desc="_calculate_new_extremeties",
@@ -1193,7 +1192,6 @@ class EventsStore(EventFederationStore, EventsWorkerStore, BackgroundUpdateStore
                     "type": event.type,
                     "processed": True,
                     "outlier": event.internal_metadata.is_outlier(),
-                    "content": encode_json(event.content).decode("UTF-8"),
                     "origin_server_ts": int(event.origin_server_ts),
                     "received_ts": self._clock.time_msec(),
                     "sender": event.sender,
diff --git a/synapse/storage/schema/delta/50/make_event_content_nullable.py b/synapse/storage/schema/delta/50/make_event_content_nullable.py
new file mode 100644
index 0000000000..7d27342e39
--- /dev/null
+++ b/synapse/storage/schema/delta/50/make_event_content_nullable.py
@@ -0,0 +1,92 @@
+# -*- 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.
+
+"""
+We want to stop populating 'event.content', so we need to make it nullable.
+
+If this has to be rolled back, then the following should populate the missing data:
+
+Postgres:
+
+    UPDATE events SET content=(ej.json::json)->'content' FROM event_json ej
+    WHERE ej.event_id = events.event_id AND
+        stream_ordering < (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering LIMIT 1
+        );
+
+    UPDATE events SET content=(ej.json::json)->'content' FROM event_json ej
+    WHERE ej.event_id = events.event_id AND
+        stream_ordering > (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering DESC LIMIT 1
+        );
+
+SQLite:
+
+    UPDATE events SET content=(
+        SELECT json_extract(json,'$.content') FROM event_json ej
+        WHERE ej.event_id = events.event_id
+    )
+    WHERE
+        stream_ordering < (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering LIMIT 1
+        )
+        OR stream_ordering > (
+            SELECT stream_ordering FROM events WHERE content IS NOT NULL
+            ORDER BY stream_ordering DESC LIMIT 1
+        );
+
+"""
+
+import logging
+
+from synapse.storage.engines import PostgresEngine
+
+logger = logging.getLogger(__name__)
+
+
+def run_create(cur, database_engine, *args, **kwargs):
+    pass
+
+
+def run_upgrade(cur, database_engine, *args, **kwargs):
+    if isinstance(database_engine, PostgresEngine):
+        cur.execute("""
+            ALTER TABLE events ALTER COLUMN content DROP NOT NULL;
+        """)
+        return
+
+    # sqlite is an arse about this. ref: https://www.sqlite.org/lang_altertable.html
+
+    cur.execute("SELECT sql FROM sqlite_master WHERE tbl_name='events' AND type='table'")
+    (oldsql,) = cur.fetchone()
+
+    sql = oldsql.replace("content TEXT NOT NULL", "content TEXT")
+    if sql == oldsql:
+        raise Exception("Couldn't find null constraint to drop in %s" % oldsql)
+
+    logger.info("Replacing definition of 'events' with: %s", sql)
+
+    cur.execute("PRAGMA schema_version")
+    (oldver,) = cur.fetchone()
+    cur.execute("PRAGMA writable_schema=ON")
+    cur.execute(
+        "UPDATE sqlite_master SET sql=? WHERE tbl_name='events' AND type='table'",
+        (sql, ),
+    )
+    cur.execute("PRAGMA schema_version=%i" % (oldver+1,))
+    cur.execute("PRAGMA writable_schema=OFF")
diff --git a/synapse/storage/schema/full_schemas/16/event_edges.sql b/synapse/storage/schema/full_schemas/16/event_edges.sql
index 52eec88357..6b5a5a88fa 100644
--- a/synapse/storage/schema/full_schemas/16/event_edges.sql
+++ b/synapse/storage/schema/full_schemas/16/event_edges.sql
@@ -37,7 +37,8 @@ CREATE TABLE IF NOT EXISTS event_edges(
     event_id TEXT NOT NULL,
     prev_event_id TEXT NOT NULL,
     room_id TEXT NOT NULL,
-    is_state BOOL NOT NULL,
+    is_state BOOL NOT NULL,  -- true if this is a prev_state edge rather than a regular
+                             -- event dag edge.
     UNIQUE (event_id, prev_event_id, room_id, is_state)
 );
 
diff --git a/synapse/storage/schema/full_schemas/16/im.sql b/synapse/storage/schema/full_schemas/16/im.sql
index ba5346806e..5f5cb8d01d 100644
--- a/synapse/storage/schema/full_schemas/16/im.sql
+++ b/synapse/storage/schema/full_schemas/16/im.sql
@@ -19,7 +19,12 @@ CREATE TABLE IF NOT EXISTS events(
     event_id TEXT NOT NULL,
     type TEXT NOT NULL,
     room_id TEXT NOT NULL,
-    content TEXT NOT NULL,
+
+    -- 'content' used to be created NULLable, but as of delta 50 we drop that constraint.
+    -- the hack we use to drop the constraint doesn't work for an in-memory sqlite
+    -- database, which breaks the sytests. Hence, we no longer make it nullable.
+    content TEXT,
+
     unrecognized_keys TEXT,
     processed BOOL NOT NULL,
     outlier BOOL NOT NULL,
diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py
index 9d85dbb1d6..b9f2b74ac6 100644
--- a/synapse/storage/stream.py
+++ b/synapse/storage/stream.py
@@ -527,7 +527,9 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             )
 
     @defer.inlineCallbacks
-    def get_events_around(self, room_id, event_id, before_limit, after_limit):
+    def get_events_around(
+        self, room_id, event_id, before_limit, after_limit, event_filter=None,
+    ):
         """Retrieve events and pagination tokens around a given event in a
         room.
 
@@ -536,6 +538,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             event_id (str)
             before_limit (int)
             after_limit (int)
+            event_filter (Filter|None)
 
         Returns:
             dict
@@ -543,7 +546,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
 
         results = yield self.runInteraction(
             "get_events_around", self._get_events_around_txn,
-            room_id, event_id, before_limit, after_limit
+            room_id, event_id, before_limit, after_limit, event_filter,
         )
 
         events_before = yield self._get_events(
@@ -563,7 +566,9 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             "end": results["after"]["token"],
         })
 
-    def _get_events_around_txn(self, txn, room_id, event_id, before_limit, after_limit):
+    def _get_events_around_txn(
+        self, txn, room_id, event_id, before_limit, after_limit, event_filter,
+    ):
         """Retrieves event_ids and pagination tokens around a given event in a
         room.
 
@@ -572,6 +577,7 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             event_id (str)
             before_limit (int)
             after_limit (int)
+            event_filter (Filter|None)
 
         Returns:
             dict
@@ -601,11 +607,13 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
 
         rows, start_token = self._paginate_room_events_txn(
             txn, room_id, before_token, direction='b', limit=before_limit,
+            event_filter=event_filter,
         )
         events_before = [r.event_id for r in rows]
 
         rows, end_token = self._paginate_room_events_txn(
             txn, room_id, after_token, direction='f', limit=after_limit,
+            event_filter=event_filter,
         )
         events_after = [r.event_id for r in rows]
 
diff --git a/synapse/storage/transactions.py b/synapse/storage/transactions.py
index b4b479d94c..428e7fa36e 100644
--- a/synapse/storage/transactions.py
+++ b/synapse/storage/transactions.py
@@ -273,7 +273,9 @@ class TransactionStore(SQLBaseStore):
         return self.cursor_to_dict(txn)
 
     def _start_cleanup_transactions(self):
-        run_as_background_process("cleanup_transactions", self._cleanup_transactions)
+        return run_as_background_process(
+            "cleanup_transactions", self._cleanup_transactions,
+        )
 
     def _cleanup_transactions(self):
         now = self._clock.time_msec()
diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index 465adc54a8..ce85b2ae11 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -64,7 +64,7 @@ class ExpiringCache(object):
             return
 
         def f():
-            run_as_background_process(
+            return run_as_background_process(
                 "prune_cache_%s" % self._cache_name,
                 self._prune_cache,
             )