Skip waiting for full state if a StateFilter does not require it

changelog.d/12498.misc

@@ -0,0 +1 @@
+Preparation for faster-room-join work: return subsets of room state which we already have, immediately.

synapse/storage/state.py

@@ -1,4 +1,5 @@
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2022 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,6 +16,7 @@
 from typing import (
  TYPE_CHECKING,
  Awaitable,
+ Callable,
  Collection,
  Dict,
  Iterable,
@@ -532,6 +534,44 @@ def approx_difference(self, other: "StateFilter") -> "StateFilter":
  new_all, new_excludes, new_wildcards, new_concrete_keys
  )
 
+ def must_await_full_state(self, is_mine_id: Callable[[str], bool]) -> bool:
+ """Check if we need to wait for full state to complete to calculate this state
+
+ If we have a state filter which is completely satisfied even with partial
+ state, then we don't need to await_full_state before we can return it.
+
+ Args:
+ is_mine_id: a callable which confirms if a given state_key matches a mxid
+ of a local user
+ """
+
+ # TODO(faster_joins): it's not entirely clear that this is safe. In particular,
+ # there may be circumstances in which we return a piece of state that, once we
+ # resync the state, we discover is invalid. For example: if it turns out that
+ # the sender of a piece of state wasn't actually in the room, then clearly that
+ # state shouldn't have been returned.
+ # We should at least add some tests around this to see what happens.
+
+ # if we haven't requested membership events, then it depends on the value of
+ # 'include_others'
+ if EventTypes.Member not in self.types:
+ return self.include_others
+
+ # if we're looking for *all* membership events, then we have to wait
+ member_state_keys = self.types[EventTypes.Member]
+ if member_state_keys is None:
+ return True
+
+ # otherwise, consider whose membership we are looking for. If it's entirely
+ # local users, then we don't need to wait.
+ for state_key in member_state_keys:
+ if not is_mine_id(state_key):
+ # remote user
+ return True
+
+ # local users only
+ return False
+
 
 _ALL_STATE_FILTER = StateFilter(types=frozendict(), include_others=True)
 _ALL_NON_MEMBER_STATE_FILTER = StateFilter(
@@ -544,6 +584,7 @@ class StateGroupStorage:
  """High level interface to fetching state for event."""
 
  def __init__(self, hs: "HomeServer", stores: "Databases"):
+ self._is_mine_id = hs.is_mine_id
  self.stores = stores
  self._partial_state_events_tracker = PartialStateEventsTracker(stores.main)
 
@@ -675,7 +716,13 @@ async def get_state_for_events(
  RuntimeError if we don't have a state group for one or more of the events
  (ie they are outliers or unknown)
  """
- event_to_groups = await self.get_state_group_for_events(event_ids)
+ await_full_state = True
+ if state_filter and not state_filter.must_await_full_state(self._is_mine_id):
+ await_full_state = False
+
+ event_to_groups = await self.get_state_group_for_events(
+ event_ids, await_full_state=await_full_state
+ )
 
  groups = set(event_to_groups.values())
  group_to_state = await self.stores.state._get_state_for_groups(
@@ -699,7 +746,9 @@ async def get_state_for_events(
  return {event: event_to_state[event] for event in event_ids}
 
  async def get_state_ids_for_events(
- self, event_ids: Collection[str], state_filter: Optional[StateFilter] = None
+ self,
+ event_ids: Collection[str],
+ state_filter: Optional[StateFilter] = None,
  ) -> Dict[str, StateMap[str]]:
  """
  Get the state dicts corresponding to a list of events, containing the event_ids
@@ -716,7 +765,13 @@ async def get_state_ids_for_events(
  RuntimeError if we don't have a state group for one or more of the events
  (ie they are outliers or unknown)
  """
- event_to_groups = await self.get_state_group_for_events(event_ids)
+ await_full_state = True
+ if state_filter and not state_filter.must_await_full_state(self._is_mine_id):
+ await_full_state = False
+
+ event_to_groups = await self.get_state_group_for_events(
+ event_ids, await_full_state=await_full_state
+ )
 
  groups = set(event_to_groups.values())
  group_to_state = await self.stores.state._get_state_for_groups(
@@ -802,7 +857,7 @@ async def get_state_group_for_events(
  Args:
  event_ids: events to get state groups for
  await_full_state: if true, will block if we do not yet have complete
- state at this event.
+ state at these events.
  """
  if await_full_state:
  await self._partial_state_events_tracker.await_full_state(event_ids)