From 0e0a2817a29391fd777f7ee683dc03d63cf40302 Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Wed, 24 Jun 2020 18:48:18 +0100 Subject: [PATCH] Yield during large v2 state res. (#7735) State res v2 across large data sets can be very CPU intensive, and if all the relevant events are in the cache the algorithm will run from start to finish within a single reactor tick. This can result in blocking the reactor tick for several seconds, which can have major repercussions on other requests. To fix this we simply add the occaisonal `sleep(0)` during iterations to yield execution until the next reactor tick. The aim is to only do this for large data sets so that we don't impact otherwise quick resolutions.= --- changelog.d/7735.bugfix | 1 + synapse/handlers/federation.py | 1 + synapse/state/__init__.py | 6 +++- synapse/state/v2.py | 56 ++++++++++++++++++++++++++++------ tests/state/test_v2.py | 9 ++++++ 5 files changed, 62 insertions(+), 11 deletions(-) create mode 100644 changelog.d/7735.bugfix diff --git a/changelog.d/7735.bugfix b/changelog.d/7735.bugfix new file mode 100644 index 000000000..86959a5ca --- /dev/null +++ b/changelog.d/7735.bugfix @@ -0,0 +1 @@ +Fix large state resolutions from stalling Synapse for seconds at a time. diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py index 873f6bc39..3828ff0ef 100644 --- a/synapse/handlers/federation.py +++ b/synapse/handlers/federation.py @@ -376,6 +376,7 @@ class FederationHandler(BaseHandler): room_version = await self.store.get_room_version_id(room_id) state_map = await resolve_events_with_store( + self.clock, room_id, room_version, state_maps, diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py index 50fd843f6..495d9f04c 100644 --- a/synapse/state/__init__.py +++ b/synapse/state/__init__.py @@ -32,6 +32,7 @@ from synapse.logging.utils import log_function from synapse.state import v1, v2 from synapse.storage.data_stores.main.events_worker import EventRedactBehaviour from synapse.types import StateMap +from synapse.util import Clock from synapse.util.async_helpers import Linearizer from synapse.util.caches.expiringcache import ExpiringCache from synapse.util.metrics import Measure, measure_func @@ -414,6 +415,7 @@ class StateHandler(object): with Measure(self.clock, "state._resolve_events"): new_state = yield resolve_events_with_store( + self.clock, event.room_id, room_version, state_set_ids, @@ -516,6 +518,7 @@ class StateResolutionHandler(object): logger.info("Resolving conflicted state for %r", room_id) with Measure(self.clock, "state._resolve_events"): new_state = yield resolve_events_with_store( + self.clock, room_id, room_version, list(state_groups_ids.values()), @@ -589,6 +592,7 @@ def _make_state_cache_entry(new_state, state_groups_ids): def resolve_events_with_store( + clock: Clock, room_id: str, room_version: str, state_sets: List[StateMap[str]], @@ -625,7 +629,7 @@ def resolve_events_with_store( ) else: return v2.resolve_events_with_store( - room_id, room_version, state_sets, event_map, state_res_store + clock, room_id, room_version, state_sets, event_map, state_res_store ) diff --git a/synapse/state/v2.py b/synapse/state/v2.py index 57eadce4e..7181ecda9 100644 --- a/synapse/state/v2.py +++ b/synapse/state/v2.py @@ -27,12 +27,20 @@ from synapse.api.errors import AuthError from synapse.api.room_versions import KNOWN_ROOM_VERSIONS from synapse.events import EventBase from synapse.types import StateMap +from synapse.util import Clock logger = logging.getLogger(__name__) +# We want to yield to the reactor occasionally during state res when dealing +# with large data sets, so that we don't exhaust the reactor. This is done by +# yielding to reactor during loops every N iterations. +_YIELD_AFTER_ITERATIONS = 100 + + @defer.inlineCallbacks def resolve_events_with_store( + clock: Clock, room_id: str, room_version: str, state_sets: List[StateMap[str]], @@ -42,13 +50,11 @@ def resolve_events_with_store( """Resolves the state using the v2 state resolution algorithm Args: + clock room_id: the room we are working in - room_version: The room version - state_sets: List of dicts of (type, state_key) -> event_id, which are the different state groups to resolve. - event_map: a dict from event_id to event, for any events that we happen to have in flight (eg, those currently being persisted). This will be @@ -113,7 +119,7 @@ def resolve_events_with_store( ) sorted_power_events = yield _reverse_topological_power_sort( - room_id, power_events, event_map, state_res_store, full_conflicted_set + clock, room_id, power_events, event_map, state_res_store, full_conflicted_set ) logger.debug("sorted %d power events", len(sorted_power_events)) @@ -142,7 +148,7 @@ def resolve_events_with_store( pl = resolved_state.get((EventTypes.PowerLevels, ""), None) leftover_events = yield _mainline_sort( - room_id, leftover_events, pl, event_map, state_res_store + clock, room_id, leftover_events, pl, event_map, state_res_store ) logger.debug("resolving remaining events") @@ -317,12 +323,13 @@ def _add_event_and_auth_chain_to_graph( @defer.inlineCallbacks def _reverse_topological_power_sort( - room_id, event_ids, event_map, state_res_store, auth_diff + clock, room_id, event_ids, event_map, state_res_store, auth_diff ): """Returns a list of the event_ids sorted by reverse topological ordering, and then by power level and origin_server_ts Args: + clock (Clock) room_id (str): the room we are working in event_ids (list[str]): The events to sort event_map (dict[str,FrozenEvent]) @@ -334,18 +341,28 @@ def _reverse_topological_power_sort( """ graph = {} - for event_id in event_ids: + for idx, event_id in enumerate(event_ids, start=1): yield _add_event_and_auth_chain_to_graph( graph, room_id, event_id, event_map, state_res_store, auth_diff ) + # We yield occasionally when we're working with large data sets to + # ensure that we don't block the reactor loop for too long. + if idx % _YIELD_AFTER_ITERATIONS == 0: + yield clock.sleep(0) + event_to_pl = {} - for event_id in graph: + for idx, event_id in enumerate(graph, start=1): pl = yield _get_power_level_for_sender( room_id, event_id, event_map, state_res_store ) event_to_pl[event_id] = pl + # We yield occasionally when we're working with large data sets to + # ensure that we don't block the reactor loop for too long. + if idx % _YIELD_AFTER_ITERATIONS == 0: + yield clock.sleep(0) + def _get_power_order(event_id): ev = event_map[event_id] pl = event_to_pl[event_id] @@ -423,12 +440,13 @@ def _iterative_auth_checks( @defer.inlineCallbacks def _mainline_sort( - room_id, event_ids, resolved_power_event_id, event_map, state_res_store + clock, room_id, event_ids, resolved_power_event_id, event_map, state_res_store ): """Returns a sorted list of event_ids sorted by mainline ordering based on the given event resolved_power_event_id Args: + clock (Clock) room_id (str): room we're working in event_ids (list[str]): Events to sort resolved_power_event_id (str): The final resolved power level event ID @@ -438,8 +456,14 @@ def _mainline_sort( Returns: Deferred[list[str]]: The sorted list """ + if not event_ids: + # It's possible for there to be no event IDs here to sort, so we can + # skip calculating the mainline in that case. + return [] + mainline = [] pl = resolved_power_event_id + idx = 0 while pl: mainline.append(pl) pl_ev = yield _get_event(room_id, pl, event_map, state_res_store) @@ -453,17 +477,29 @@ def _mainline_sort( pl = aid break + # We yield occasionally when we're working with large data sets to + # ensure that we don't block the reactor loop for too long. + if idx != 0 and idx % _YIELD_AFTER_ITERATIONS == 0: + yield clock.sleep(0) + + idx += 1 + mainline_map = {ev_id: i + 1 for i, ev_id in enumerate(reversed(mainline))} event_ids = list(event_ids) order_map = {} - for ev_id in event_ids: + for idx, ev_id in enumerate(event_ids, start=1): depth = yield _get_mainline_depth_for_event( event_map[ev_id], mainline_map, event_map, state_res_store ) order_map[ev_id] = (depth, event_map[ev_id].origin_server_ts, ev_id) + # We yield occasionally when we're working with large data sets to + # ensure that we don't block the reactor loop for too long. + if idx % _YIELD_AFTER_ITERATIONS == 0: + yield clock.sleep(0) + event_ids.sort(key=lambda ev_id: order_map[ev_id]) return event_ids diff --git a/tests/state/test_v2.py b/tests/state/test_v2.py index cdc347bc5..38f9b423e 100644 --- a/tests/state/test_v2.py +++ b/tests/state/test_v2.py @@ -17,6 +17,8 @@ import itertools import attr +from twisted.internet import defer + from synapse.api.constants import EventTypes, JoinRules, Membership from synapse.api.room_versions import RoomVersions from synapse.event_auth import auth_types_for_event @@ -41,6 +43,11 @@ MEMBERSHIP_CONTENT_BAN = {"membership": Membership.BAN} ORIGIN_SERVER_TS = 0 +class FakeClock: + def sleep(self, msec): + return defer.succeed(None) + + class FakeEvent(object): """A fake event we use as a convenience. @@ -417,6 +424,7 @@ class StateTestCase(unittest.TestCase): state_before = dict(state_at_event[prev_events[0]]) else: state_d = resolve_events_with_store( + FakeClock(), ROOM_ID, RoomVersions.V2.identifier, [state_at_event[n] for n in prev_events], @@ -565,6 +573,7 @@ class SimpleParamStateTestCase(unittest.TestCase): # Test that we correctly handle passing `None` as the event_map state_d = resolve_events_with_store( + FakeClock(), ROOM_ID, RoomVersions.V2.identifier, [self.state_at_bob, self.state_at_charlie],