From 58d93444e91c2f383670f4911ce639e99a8b8853 Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Mon, 8 Apr 2024 11:32:36 +0100 Subject: [PATCH] Add back fast path for non-gappy syncs PR #16942 removed an invalid optimisation that avoided pulling out state for non-gappy syncs. This causes a large increase in DB usage. c.f. #16941 for why that optimisation was wrong. However, we can still optimise in the simple case where the events in the timeline are a linear chain without any branching/merging of the DAG. --- synapse/handlers/sync.py | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py index 554c820f79..369878d6bf 100644 --- a/synapse/handlers/sync.py +++ b/synapse/handlers/sync.py @@ -1259,6 +1259,34 @@ async def _compute_state_delta_for_incremental_sync( await_full_state = True lazy_load_members = False + # For a non-gappy sync if the events in the timeline are simply a linear + # chain (i.e. no merging/branching of the graph), then we know the state + # delta between the end of the previous sync and start of the new one is + # empty. + # + # c.f. #16941 for an example of why we can't do this for all non-gappy + # syncs. + is_linear_timeline = all(len(e.prev_event_ids()) <= 1 for e in batch.events) + if is_linear_timeline and not batch.limited: + state_ids: StateMap[str] = {} + if lazy_load_members: + if members_to_fetch and batch.events: + # We're lazy-loading, so the client might need some more + # member events to understand the events in this timeline. + # So we fish out all the member events corresponding to the + # timeline here. The caller will then dedupe any redundant + # ones. + + state_ids = await self._state_storage_controller.get_state_ids_for_event( + batch.events[0].event_id, + # we only want members! + state_filter=StateFilter.from_types( + (EventTypes.Member, member) for member in members_to_fetch + ), + await_full_state=False, + ) + return state_ids + if batch: state_at_timeline_start = ( await self._state_storage_controller.get_state_ids_for_event(