Cap the number of in-flight requests for state from a single group (#11608)

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reivilibre 2022-02-22 14:24:31 +00:00 committed by GitHub
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changelog.d/11608.misc Normal file
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@ -0,0 +1 @@
Deduplicate in-flight requests in `_get_state_for_groups`.

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@ -56,6 +56,7 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
MAX_STATE_DELTA_HOPS = 100
MAX_INFLIGHT_REQUESTS_PER_GROUP = 5
@attr.s(slots=True, frozen=True, auto_attribs=True)
@ -258,6 +259,11 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
Attempts to gather in-flight requests and re-use them to retrieve state
for the given state group, filtered with the given state filter.
If there are more than MAX_INFLIGHT_REQUESTS_PER_GROUP in-flight requests,
and there *still* isn't enough information to complete the request by solely
reusing others, a full state filter will be requested to ensure that subsequent
requests can reuse this request.
Used as part of _get_state_for_group_using_inflight_cache.
Returns:
@ -288,6 +294,16 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
# to cover our StateFilter and give us the state we need.
break
if (
state_filter_left_over != StateFilter.none()
and len(inflight_requests) >= MAX_INFLIGHT_REQUESTS_PER_GROUP
):
# There are too many requests for this group.
# To prevent even more from building up, we request the whole
# state filter to guarantee that we can be reused by any subsequent
# requests for this state group.
return (), StateFilter.all()
return reusable_requests, state_filter_left_over
async def _get_state_for_group_fire_request(

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@ -19,6 +19,7 @@ from twisted.internet.defer import Deferred, ensureDeferred
from twisted.test.proto_helpers import MemoryReactor
from synapse.api.constants import EventTypes
from synapse.storage.databases.state.store import MAX_INFLIGHT_REQUESTS_PER_GROUP
from synapse.storage.state import StateFilter
from synapse.types import StateMap
from synapse.util import Clock
@ -281,3 +282,71 @@ class StateGroupInflightCachingTestCase(HomeserverTestCase):
self.assertEqual(self.get_success(req1), FAKE_STATE)
self.assertEqual(self.get_success(req2), FAKE_STATE)
def test_inflight_requests_capped(self) -> None:
"""
Tests that the number of in-flight requests is capped to 5.
- requests several pieces of state separately
(5 to hit the limit, 1 to 'shunt out', another that comes after the
group has been 'shunted out')
- checks to see that the torrent of requests is shunted out by
rewriting one of the filters as the 'all' state filter
- requests after that one do not cause any additional queries
"""
# 5 at the time of writing.
CAP_COUNT = MAX_INFLIGHT_REQUESTS_PER_GROUP
reqs = []
# Request 7 different keys (1 to 7) of the `some.state` type.
for req_id in range(CAP_COUNT + 2):
reqs.append(
ensureDeferred(
self.state_datastore._get_state_for_group_using_inflight_cache(
42,
StateFilter.freeze(
{"some.state": {str(req_id + 1)}}, include_others=False
),
)
)
)
self.pump(by=0.1)
# There should only be 6 calls to the database, not 7.
self.assertEqual(len(self.get_state_group_calls), CAP_COUNT + 1)
# Assert that the first 5 are exact requests for the individual pieces
# wanted
for req_id in range(CAP_COUNT):
groups, sf, d = self.get_state_group_calls[req_id]
self.assertEqual(
sf,
StateFilter.freeze(
{"some.state": {str(req_id + 1)}}, include_others=False
),
)
# The 6th request should be the 'all' state filter
groups, sf, d = self.get_state_group_calls[CAP_COUNT]
self.assertEqual(sf, StateFilter.all())
# Complete the queries and check which requests complete as a result
for req_id in range(CAP_COUNT):
# This request should not have been completed yet
self.assertFalse(reqs[req_id].called)
groups, sf, d = self.get_state_group_calls[req_id]
self._complete_request_fake(groups, sf, d)
# This should have only completed this one request
self.assertTrue(reqs[req_id].called)
# Now complete the final query; the last 2 requests should complete
# as a result
self.assertFalse(reqs[CAP_COUNT].called)
self.assertFalse(reqs[CAP_COUNT + 1].called)
groups, sf, d = self.get_state_group_calls[CAP_COUNT]
self._complete_request_fake(groups, sf, d)
self.assertTrue(reqs[CAP_COUNT].called)
self.assertTrue(reqs[CAP_COUNT + 1].called)