diff --git a/changelog.d/10870.misc b/changelog.d/10870.misc
new file mode 100644
index 0000000000..3af049b969
--- /dev/null
+++ b/changelog.d/10870.misc
@@ -0,0 +1 @@
+Deduplicate in-flight requests in `_get_state_for_groups`.
diff --git a/synapse/storage/databases/state/store.py b/synapse/storage/databases/state/store.py
index 7614d76ac6..3af69a2076 100644
--- a/synapse/storage/databases/state/store.py
+++ b/synapse/storage/databases/state/store.py
@@ -13,11 +13,23 @@
# limitations under the License.
import logging
-from typing import TYPE_CHECKING, Collection, Dict, Iterable, List, Optional, Set, Tuple
+from typing import (
+ TYPE_CHECKING,
+ Collection,
+ Dict,
+ Iterable,
+ Optional,
+ Sequence,
+ Set,
+ Tuple,
+)
import attr
+from twisted.internet import defer
+
from synapse.api.constants import EventTypes
+from synapse.logging.context import make_deferred_yieldable, run_in_background
from synapse.storage._base import SQLBaseStore
from synapse.storage.database import (
DatabasePool,
@@ -29,6 +41,12 @@ from synapse.storage.state import StateFilter
from synapse.storage.types import Cursor
from synapse.storage.util.sequence import build_sequence_generator
from synapse.types import MutableStateMap, StateKey, StateMap
+from synapse.util import unwrapFirstError
+from synapse.util.async_helpers import (
+ AbstractObservableDeferred,
+ ObservableDeferred,
+ yieldable_gather_results,
+)
from synapse.util.caches.descriptors import cached
from synapse.util.caches.dictionary_cache import DictionaryCache
@@ -37,7 +55,6 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
-
MAX_STATE_DELTA_HOPS = 100
@@ -106,6 +123,12 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
500000,
)
+ # Current ongoing get_state_for_groups in-flight requests
+ # {group ID -> {StateFilter -> ObservableDeferred}}
+ self._state_group_inflight_requests: Dict[
+ int, Dict[StateFilter, AbstractObservableDeferred[StateMap[str]]]
+ ] = {}
+
def get_max_state_group_txn(txn: Cursor) -> int:
txn.execute("SELECT COALESCE(max(id), 0) FROM state_groups")
return txn.fetchone()[0] # type: ignore
@@ -157,7 +180,7 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
)
async def _get_state_groups_from_groups(
- self, groups: List[int], state_filter: StateFilter
+ self, groups: Sequence[int], state_filter: StateFilter
) -> Dict[int, StateMap[str]]:
"""Returns the state groups for a given set of groups from the
database, filtering on types of state events.
@@ -228,6 +251,150 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
return state_filter.filter_state(state_dict_ids), not missing_types
+ def _get_state_for_group_gather_inflight_requests(
+ self, group: int, state_filter_left_over: StateFilter
+ ) -> Tuple[Sequence[AbstractObservableDeferred[StateMap[str]]], StateFilter]:
+ """
+ Attempts to gather in-flight requests and re-use them to retrieve state
+ for the given state group, filtered with the given state filter.
+
+ Used as part of _get_state_for_group_using_inflight_cache.
+
+ Returns:
+ Tuple of two values:
+ A sequence of ObservableDeferreds to observe
+ A StateFilter representing what else needs to be requested to fulfill the request
+ """
+
+ inflight_requests = self._state_group_inflight_requests.get(group)
+ if inflight_requests is None:
+ # no requests for this group, need to retrieve it all ourselves
+ return (), state_filter_left_over
+
+ # The list of ongoing requests which will help narrow the current request.
+ reusable_requests = []
+ for (request_state_filter, request_deferred) in inflight_requests.items():
+ new_state_filter_left_over = state_filter_left_over.approx_difference(
+ request_state_filter
+ )
+ if new_state_filter_left_over == state_filter_left_over:
+ # Reusing this request would not gain us anything, so don't bother.
+ continue
+
+ reusable_requests.append(request_deferred)
+ state_filter_left_over = new_state_filter_left_over
+ if state_filter_left_over == StateFilter.none():
+ # we have managed to collect enough of the in-flight requests
+ # to cover our StateFilter and give us the state we need.
+ break
+
+ return reusable_requests, state_filter_left_over
+
+ async def _get_state_for_group_fire_request(
+ self, group: int, state_filter: StateFilter
+ ) -> StateMap[str]:
+ """
+ Fires off a request to get the state at a state group,
+ potentially filtering by type and/or state key.
+
+ This request will be tracked in the in-flight request cache and automatically
+ removed when it is finished.
+
+ Used as part of _get_state_for_group_using_inflight_cache.
+
+ Args:
+ group: ID of the state group for which we want to get state
+ state_filter: the state filter used to fetch state from the database
+ """
+ cache_sequence_nm = self._state_group_cache.sequence
+ cache_sequence_m = self._state_group_members_cache.sequence
+
+ # Help the cache hit ratio by expanding the filter a bit
+ db_state_filter = state_filter.return_expanded()
+
+ async def _the_request() -> StateMap[str]:
+ group_to_state_dict = await self._get_state_groups_from_groups(
+ (group,), state_filter=db_state_filter
+ )
+
+ # Now let's update the caches
+ self._insert_into_cache(
+ group_to_state_dict,
+ db_state_filter,
+ cache_seq_num_members=cache_sequence_m,
+ cache_seq_num_non_members=cache_sequence_nm,
+ )
+
+ # Remove ourselves from the in-flight cache
+ group_request_dict = self._state_group_inflight_requests[group]
+ del group_request_dict[db_state_filter]
+ if not group_request_dict:
+ # If there are no more requests in-flight for this group,
+ # clean up the cache by removing the empty dictionary
+ del self._state_group_inflight_requests[group]
+
+ return group_to_state_dict[group]
+
+ # We don't immediately await the result, so must use run_in_background
+ # But we DO await the result before the current log context (request)
+ # finishes, so don't need to run it as a background process.
+ request_deferred = run_in_background(_the_request)
+ observable_deferred = ObservableDeferred(request_deferred, consumeErrors=True)
+
+ # Insert the ObservableDeferred into the cache
+ group_request_dict = self._state_group_inflight_requests.setdefault(group, {})
+ group_request_dict[db_state_filter] = observable_deferred
+
+ return await make_deferred_yieldable(observable_deferred.observe())
+
+ async def _get_state_for_group_using_inflight_cache(
+ self, group: int, state_filter: StateFilter
+ ) -> MutableStateMap[str]:
+ """
+ Gets the state at a state group, potentially filtering by type and/or
+ state key.
+
+ 1. Calls _get_state_for_group_gather_inflight_requests to gather any
+ ongoing requests which might overlap with the current request.
+ 2. Fires a new request, using _get_state_for_group_fire_request,
+ for any state which cannot be gathered from ongoing requests.
+
+ Args:
+ group: ID of the state group for which we want to get state
+ state_filter: the state filter used to fetch state from the database
+ Returns:
+ state map
+ """
+
+ # first, figure out whether we can re-use any in-flight requests
+ # (and if so, what would be left over)
+ (
+ reusable_requests,
+ state_filter_left_over,
+ ) = self._get_state_for_group_gather_inflight_requests(group, state_filter)
+
+ if state_filter_left_over != StateFilter.none():
+ # Fetch remaining state
+ remaining = await self._get_state_for_group_fire_request(
+ group, state_filter_left_over
+ )
+ assembled_state: MutableStateMap[str] = dict(remaining)
+ else:
+ assembled_state = {}
+
+ gathered = await make_deferred_yieldable(
+ defer.gatherResults(
+ (r.observe() for r in reusable_requests), consumeErrors=True
+ )
+ ).addErrback(unwrapFirstError)
+
+ # assemble our result.
+ for result_piece in gathered:
+ assembled_state.update(result_piece)
+
+ # Filter out any state that may be more than what we asked for.
+ return state_filter.filter_state(assembled_state)
+
async def _get_state_for_groups(
self, groups: Iterable[int], state_filter: Optional[StateFilter] = None
) -> Dict[int, MutableStateMap[str]]:
@@ -269,31 +436,17 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
if not incomplete_groups:
return state
- cache_sequence_nm = self._state_group_cache.sequence
- cache_sequence_m = self._state_group_members_cache.sequence
-
- # Help the cache hit ratio by expanding the filter a bit
- db_state_filter = state_filter.return_expanded()
-
- group_to_state_dict = await self._get_state_groups_from_groups(
- list(incomplete_groups), state_filter=db_state_filter
- )
+ async def get_from_cache(group: int, state_filter: StateFilter) -> None:
+ state[group] = await self._get_state_for_group_using_inflight_cache(
+ group, state_filter
+ )
- # Now lets update the caches
- self._insert_into_cache(
- group_to_state_dict,
- db_state_filter,
- cache_seq_num_members=cache_sequence_m,
- cache_seq_num_non_members=cache_sequence_nm,
+ await yieldable_gather_results(
+ get_from_cache,
+ incomplete_groups,
+ state_filter,
)
- # And finally update the result dict, by filtering out any extra
- # stuff we pulled out of the database.
- for group, group_state_dict in group_to_state_dict.items():
- # We just replace any existing entries, as we will have loaded
- # everything we need from the database anyway.
- state[group] = state_filter.filter_state(group_state_dict)
-
return state
def _get_state_for_groups_using_cache(
diff --git a/tests/storage/databases/test_state_store.py b/tests/storage/databases/test_state_store.py
new file mode 100644
index 0000000000..cf126ee62d
--- /dev/null
+++ b/tests/storage/databases/test_state_store.py
@@ -0,0 +1,133 @@
+# 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.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import typing
+from typing import Dict, List, Sequence, Tuple
+from unittest.mock import patch
+
+from twisted.internet.defer import Deferred, ensureDeferred
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.storage.state import StateFilter
+from synapse.types import MutableStateMap, StateMap
+from synapse.util import Clock
+
+from tests.unittest import HomeserverTestCase
+
+if typing.TYPE_CHECKING:
+ from synapse.server import HomeServer
+
+
+class StateGroupInflightCachingTestCase(HomeserverTestCase):
+ def prepare(
+ self, reactor: MemoryReactor, clock: Clock, homeserver: "HomeServer"
+ ) -> None:
+ self.state_storage = homeserver.get_storage().state
+ self.state_datastore = homeserver.get_datastores().state
+ # Patch out the `_get_state_groups_from_groups`.
+ # This is useful because it lets us pretend we have a slow database.
+ get_state_groups_patch = patch.object(
+ self.state_datastore,
+ "_get_state_groups_from_groups",
+ self._fake_get_state_groups_from_groups,
+ )
+ get_state_groups_patch.start()
+
+ self.addCleanup(get_state_groups_patch.stop)
+ self.get_state_group_calls: List[
+ Tuple[Tuple[int, ...], StateFilter, Deferred[Dict[int, StateMap[str]]]]
+ ] = []
+
+ def _fake_get_state_groups_from_groups(
+ self, groups: Sequence[int], state_filter: StateFilter
+ ) -> "Deferred[Dict[int, StateMap[str]]]":
+ d: Deferred[Dict[int, StateMap[str]]] = Deferred()
+ self.get_state_group_calls.append((tuple(groups), state_filter, d))
+ return d
+
+ def _complete_request_fake(
+ self,
+ groups: Tuple[int, ...],
+ state_filter: StateFilter,
+ d: "Deferred[Dict[int, StateMap[str]]]",
+ ) -> None:
+ """
+ Assemble a fake database response and complete the database request.
+ """
+
+ result: Dict[int, StateMap[str]] = {}
+
+ for group in groups:
+ group_result: MutableStateMap[str] = {}
+ result[group] = group_result
+
+ for state_type, state_keys in state_filter.types.items():
+ if state_keys is None:
+ group_result[(state_type, "a")] = "xyz"
+ group_result[(state_type, "b")] = "xyz"
+ else:
+ for state_key in state_keys:
+ group_result[(state_type, state_key)] = "abc"
+
+ if state_filter.include_others:
+ group_result[("other.event.type", "state.key")] = "123"
+
+ d.callback(result)
+
+ def test_duplicate_requests_deduplicated(self) -> None:
+ """
+ Tests that duplicate requests for state are deduplicated.
+
+ This test:
+ - requests some state (state group 42, 'all' state filter)
+ - requests it again, before the first request finishes
+ - checks to see that only one database query was made
+ - completes the database query
+ - checks that both requests see the same retrieved state
+ """
+ req1 = ensureDeferred(
+ self.state_datastore._get_state_for_group_using_inflight_cache(
+ 42, StateFilter.all()
+ )
+ )
+ self.pump(by=0.1)
+
+ # This should have gone to the database
+ self.assertEqual(len(self.get_state_group_calls), 1)
+ self.assertFalse(req1.called)
+
+ req2 = ensureDeferred(
+ self.state_datastore._get_state_for_group_using_inflight_cache(
+ 42, StateFilter.all()
+ )
+ )
+ self.pump(by=0.1)
+
+ # No more calls should have gone to the database
+ self.assertEqual(len(self.get_state_group_calls), 1)
+ self.assertFalse(req1.called)
+ self.assertFalse(req2.called)
+
+ groups, sf, d = self.get_state_group_calls[0]
+ self.assertEqual(groups, (42,))
+ self.assertEqual(sf, StateFilter.all())
+
+ # Now we can complete the request
+ self._complete_request_fake(groups, sf, d)
+
+ self.assertEqual(
+ self.get_success(req1), {("other.event.type", "state.key"): "123"}
+ )
+ self.assertEqual(
+ self.get_success(req2), {("other.event.type", "state.key"): "123"}
+ )
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