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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.=
This commit is contained in:
Erik Johnston 2020-06-24 18:48:18 +01:00 committed by GitHub
parent 6920e58136
commit 0e0a2817a2
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GPG Key ID: 4AEE18F83AFDEB23
5 changed files with 62 additions and 11 deletions
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1
changelog.d/7735.bugfix Normal file
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@ -0,0 +1 @@
Fix large state resolutions from stalling Synapse for seconds at a time.

1
synapse/handlers/federation.py
View File

@ -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,

6
synapse/state/__init__.py
View File

@ -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
)

56
synapse/state/v2.py
View File

@ -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

9
tests/state/test_v2.py
View File

@ -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],