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Sliding Sync: Look for bump _stamp in the room timeline (#17684)
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This allows us to skip checking the database a lot of the time.

---------

Co-authored-by: Eric Eastwood <eric.eastwood@beta.gouv.fr>
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@erikjohnston @MadLittleMods
erikjohnston and MadLittleMods committed Sep 10, 2024
1 parent 588e5b5 commit 9689ac3
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Showing 2 changed files with 96 additions and 53 deletions.
1 change: 1 addition & 0 deletions changelog.d/17684.misc
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Speed up sliding sync by reducing number of database calls.
148 changes: 95 additions & 53 deletions synapse/handlers/sliding_sync/__init__.py
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Expand Up @@ -1031,60 +1031,13 @@ async def get_room_sync_data(
# If we're joined to the room, we need to find the last bump event before the
# `to_token`
if room_membership_for_user_at_to_token.membership == Membership.JOIN:
# We can quickly query for the latest bump event in the room using the
# sliding sync tables.
latest_room_bump_stamp = await self.store.get_latest_bump_stamp_for_room(
room_id
# Try and get a bump stamp, if not we just fall back to the
# membership token.
new_bump_stamp = await self._get_bump_stamp(
room_id, to_token, timeline_events
)

min_to_token_position = to_token.room_key.stream

# If we can rely on the new sliding sync tables and the `bump_stamp` is
# `None`, just fallback to the membership event position. This can happen
# when we've just joined a remote room and all the events are backfilled.
if (
# FIXME: The background job check can be removed once we bump
# `SCHEMA_COMPAT_VERSION` and run the foreground update for
# `sliding_sync_joined_rooms`/`sliding_sync_membership_snapshots`
# (tracked by https://github.com/element-hq/synapse/issues/17623)
await self.store.have_finished_sliding_sync_background_jobs()
and latest_room_bump_stamp is None
):
pass

# The `bump_stamp` stored in the database might be ahead of our token. Since
# `bump_stamp` is only a `stream_ordering` position, we can't be 100% sure
# that's before the `to_token` in all scenarios. The only scenario we can be
# sure of is if the `bump_stamp` is totally before the minimum position from
# the token.
#
# We don't need to check if the background update has finished, as if the
# returned bump stamp is not None then it must be up to date.
elif (
latest_room_bump_stamp is not None
and latest_room_bump_stamp < min_to_token_position
):
bump_stamp = latest_room_bump_stamp

# Otherwise, if it's within or after the `to_token`, we need to find the
# last bump event before the `to_token`.
else:
last_bump_event_result = (
await self.store.get_last_event_pos_in_room_before_stream_ordering(
room_id,
to_token.room_key,
event_types=SLIDING_SYNC_DEFAULT_BUMP_EVENT_TYPES,
)
)
if last_bump_event_result is not None:
_, new_bump_event_pos = last_bump_event_result

# If we've just joined a remote room, then the last bump event may
# have been backfilled (and so have a negative stream ordering).
# These negative stream orderings can't sensibly be compared, so
# instead we use the membership event position.
if new_bump_event_pos.stream > 0:
bump_stamp = new_bump_event_pos.stream
if new_bump_stamp is not None:
bump_stamp = new_bump_stamp

unstable_expanded_timeline = False
prev_room_sync_config = previous_connection_state.room_configs.get(room_id)
Expand Down Expand Up @@ -1174,3 +1127,92 @@ async def get_room_sync_data(
notification_count=0,
highlight_count=0,
)

@trace
async def _get_bump_stamp(
self, room_id: str, to_token: StreamToken, timeline: List[EventBase]
) -> Optional[int]:
"""Get a bump stamp for the room, if we have a bump event
Args:
room_id
to_token: The upper bound of token to return
timeline: The list of events we have fetched.
"""

# First check the timeline events we're returning to see if one of
# those matches. We iterate backwards and take the stream ordering
# of the first event that matches the bump event types.
for timeline_event in reversed(timeline):
if timeline_event.type in SLIDING_SYNC_DEFAULT_BUMP_EVENT_TYPES:
new_bump_stamp = timeline_event.internal_metadata.stream_ordering

# All persisted events have a stream ordering
assert new_bump_stamp is not None

# If we've just joined a remote room, then the last bump event may
# have been backfilled (and so have a negative stream ordering).
# These negative stream orderings can't sensibly be compared, so
# instead we use the membership event position.
if new_bump_stamp > 0:
return new_bump_stamp

# We can quickly query for the latest bump event in the room using the
# sliding sync tables.
latest_room_bump_stamp = await self.store.get_latest_bump_stamp_for_room(
room_id
)

min_to_token_position = to_token.room_key.stream

# If we can rely on the new sliding sync tables and the `bump_stamp` is
# `None`, just fallback to the membership event position. This can happen
# when we've just joined a remote room and all the events are backfilled.
if (
# FIXME: The background job check can be removed once we bump
# `SCHEMA_COMPAT_VERSION` and run the foreground update for
# `sliding_sync_joined_rooms`/`sliding_sync_membership_snapshots`
# (tracked by https://github.com/element-hq/synapse/issues/17623)
await self.store.have_finished_sliding_sync_background_jobs()
and latest_room_bump_stamp is None
):
return None

# The `bump_stamp` stored in the database might be ahead of our token. Since
# `bump_stamp` is only a `stream_ordering` position, we can't be 100% sure
# that's before the `to_token` in all scenarios. The only scenario we can be
# sure of is if the `bump_stamp` is totally before the minimum position from
# the token.
#
# We don't need to check if the background update has finished, as if the
# returned bump stamp is not None then it must be up to date.
elif (
latest_room_bump_stamp is not None
and latest_room_bump_stamp < min_to_token_position
):
if latest_room_bump_stamp > 0:
return latest_room_bump_stamp
else:
return None

# Otherwise, if it's within or after the `to_token`, we need to find the
# last bump event before the `to_token`.
else:
last_bump_event_result = (
await self.store.get_last_event_pos_in_room_before_stream_ordering(
room_id,
to_token.room_key,
event_types=SLIDING_SYNC_DEFAULT_BUMP_EVENT_TYPES,
)
)
if last_bump_event_result is not None:
_, new_bump_event_pos = last_bump_event_result

# If we've just joined a remote room, then the last bump event may
# have been backfilled (and so have a negative stream ordering).
# These negative stream orderings can't sensibly be compared, so
# instead we use the membership event position.
if new_bump_event_pos.stream > 0:
return new_bump_event_pos.stream

return None

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