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Improve performance of backfilling in large rooms. (#9935)

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We were pulling the full auth chain for the room out of the DB each time
we backfilled, which can be *huge* for large rooms and is totally
unnecessary.
This commit is contained in:
Erik Johnston 2021-05-10 13:29:02 +01:00 committed by GitHub
parent 51065c44bb
commit 2b2985b5cf
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2 changed files with 59 additions and 73 deletions
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changelog.d/9935.feature Normal file
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@ -0,0 +1 @@
Improve performance of backfilling in large rooms.

129
synapse/handlers/federation.py
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@ -552,8 +552,12 @@ class FederationHandler(BaseHandler):
destination: str,
room_id: str,
event_id: str,
) -> Tuple[List[EventBase], List[EventBase]]:
"""Requests all of the room state at a given event from a remote homeserver.
) -> List[EventBase]:
"""Requests all of the room state at a given event from a remote
homeserver.
Will also fetch any missing events reported in the `auth_chain_ids`
section of `/state_ids`.
Args:
destination: The remote homeserver to query for the state.
@ -561,8 +565,7 @@ class FederationHandler(BaseHandler):
event_id: The id of the event we want the state at.
Returns:
A list of events in the state, not including the event itself, and
a list of events in the auth chain for the given event.
A list of events in the state, not including the event itself.
"""
(
state_event_ids,
@ -571,68 +574,53 @@ class FederationHandler(BaseHandler):
destination, room_id, event_id=event_id
)
desired_events = set(state_event_ids + auth_event_ids)
event_map = await self._get_events_from_store_or_dest(
destination, room_id, desired_events
)
failed_to_fetch = desired_events - event_map.keys()
if failed_to_fetch:
logger.warning(
"Failed to fetch missing state/auth events for %s %s",
event_id,
failed_to_fetch,
)
remote_state = [
event_map[e_id] for e_id in state_event_ids if e_id in event_map
]
auth_chain = [event_map[e_id] for e_id in auth_event_ids if e_id in event_map]
auth_chain.sort(key=lambda e: e.depth)
return remote_state, auth_chain
async def _get_events_from_store_or_dest(
self, destination: str, room_id: str, event_ids: Iterable[str]
) -> Dict[str, EventBase]:
"""Fetch events from a remote destination, checking if we already have them.
Persists any events we don't already have as outliers.
If we fail to fetch any of the events, a warning will be logged, and the event
will be omitted from the result. Likewise, any events which turn out not to
be in the given room.
This function *does not* automatically get missing auth events of the
newly fetched events. Callers must include the full auth chain of
of the missing events in the `event_ids` argument, to ensure that any
missing auth events are correctly fetched.
Returns:
map from event_id to event
"""
fetched_events = await self.store.get_events(event_ids, allow_rejected=True)
missing_events = set(event_ids) - fetched_events.keys()
if missing_events:
logger.debug(
"Fetching unknown state/auth events %s for room %s",
missing_events,
room_id,
)
# Fetch the state events from the DB, and check we have the auth events.
event_map = await self.store.get_events(state_event_ids, allow_rejected=True)
auth_events_in_store = await self.store.have_seen_events(auth_event_ids)
# Check for missing events. We handle state and auth event seperately,
# as we want to pull the state from the DB, but we don't for the auth
# events. (Note: we likely won't use the majority of the auth chain, and
# it can be *huge* for large rooms, so it's worth ensuring that we don't
# unnecessarily pull it from the DB).
missing_state_events = set(state_event_ids) - set(event_map)
missing_auth_events = set(auth_event_ids) - set(auth_events_in_store)
if missing_state_events or missing_auth_events:
await self._get_events_and_persist(
destination=destination, room_id=room_id, events=missing_events
destination=destination,
room_id=room_id,
events=missing_state_events | missing_auth_events,
)
# we need to make sure we re-load from the database to get the rejected
# state correct.
fetched_events.update(
(await self.store.get_events(missing_events, allow_rejected=True))
if missing_state_events:
new_events = await self.store.get_events(
missing_state_events, allow_rejected=True
)
event_map.update(new_events)
missing_state_events.difference_update(new_events)
if missing_state_events:
logger.warning(
"Failed to fetch missing state events for %s %s",
event_id,
missing_state_events,
)
if missing_auth_events:
auth_events_in_store = await self.store.have_seen_events(
missing_auth_events
)
missing_auth_events.difference_update(auth_events_in_store)
if missing_auth_events:
logger.warning(
"Failed to fetch missing auth events for %s %s",
event_id,
missing_auth_events,
)
remote_state = list(event_map.values())
# check for events which were in the wrong room.
#
@ -640,8 +628,8 @@ class FederationHandler(BaseHandler):
# auth_events at an event in room A are actually events in room B
bad_events = [
(event_id, event.room_id)
for event_id, event in fetched_events.items()
(event.event_id, event.room_id)
for event in remote_state
if event.room_id != room_id
]
@ -658,9 +646,10 @@ class FederationHandler(BaseHandler):
room_id,
)
del fetched_events[bad_event_id]
if bad_events:
remote_state = [e for e in remote_state if e.room_id == room_id]
return fetched_events
return remote_state
async def _get_state_after_missing_prev_event(
self,
@ -963,27 +952,23 @@ class FederationHandler(BaseHandler):
# For each edge get the current state.
auth_events = {}
state_events = {}
events_to_state = {}
for e_id in edges:
state, auth = await self._get_state_for_room(
state = await self._get_state_for_room(
destination=dest,
room_id=room_id,
event_id=e_id,
)
auth_events.update({a.event_id: a for a in auth})
auth_events.update({s.event_id: s for s in state})
state_events.update({s.event_id: s for s in state})
events_to_state[e_id] = state
required_auth = {
a_id
for event in events
+ list(state_events.values())
+ list(auth_events.values())
for event in events + list(state_events.values())
for a_id in event.auth_event_ids()
}
auth_events = await self.store.get_events(required_auth, allow_rejected=True)
auth_events.update(
{e_id: event_map[e_id] for e_id in required_auth if e_id in event_map}
)