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https://github.com/element-hq/synapse
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Multiple calls to `EventsWorkerStore._get_events_from_cache_or_db` can reuse the same database fetch, which is initiated by the first call. Ensure that cancelling the first call doesn't cancel the other calls sharing the same database fetch. Signed-off-by: Sean Quah <seanq@element.io>
400 lines
15 KiB
Python
400 lines
15 KiB
Python
# Copyright 2021 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import json
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from contextlib import contextmanager
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from typing import Generator, Tuple
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from unittest import mock
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from twisted.enterprise.adbapi import ConnectionPool
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from twisted.internet.defer import CancelledError, Deferred, ensureDeferred
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from twisted.test.proto_helpers import MemoryReactor
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from synapse.api.room_versions import EventFormatVersions, RoomVersions
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from synapse.logging.context import LoggingContext
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from synapse.rest import admin
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from synapse.rest.client import login, room
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from synapse.server import HomeServer
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from synapse.storage.databases.main.events_worker import (
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EVENT_QUEUE_THREADS,
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EventsWorkerStore,
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)
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from synapse.storage.types import Connection
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from synapse.util import Clock
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from synapse.util.async_helpers import yieldable_gather_results
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from tests import unittest
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class HaveSeenEventsTestCase(unittest.HomeserverTestCase):
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def prepare(self, reactor, clock, hs):
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self.store: EventsWorkerStore = hs.get_datastores().main
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# insert some test data
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for rid in ("room1", "room2"):
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self.get_success(
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self.store.db_pool.simple_insert(
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"rooms",
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{"room_id": rid, "room_version": 4},
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)
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)
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for idx, (rid, eid) in enumerate(
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(
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("room1", "event10"),
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("room1", "event11"),
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("room1", "event12"),
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("room2", "event20"),
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)
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):
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self.get_success(
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self.store.db_pool.simple_insert(
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"events",
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{
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"event_id": eid,
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"room_id": rid,
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"topological_ordering": idx,
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"stream_ordering": idx,
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"type": "test",
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"processed": True,
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"outlier": False,
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},
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)
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)
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self.get_success(
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self.store.db_pool.simple_insert(
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"event_json",
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{
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"event_id": eid,
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"room_id": rid,
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"json": json.dumps({"type": "test", "room_id": rid}),
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"internal_metadata": "{}",
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"format_version": 3,
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},
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)
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)
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def test_simple(self):
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with LoggingContext(name="test") as ctx:
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res = self.get_success(
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self.store.have_seen_events("room1", ["event10", "event19"])
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)
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self.assertEqual(res, {"event10"})
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# that should result in a single db query
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self.assertEqual(ctx.get_resource_usage().db_txn_count, 1)
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# a second lookup of the same events should cause no queries
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with LoggingContext(name="test") as ctx:
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res = self.get_success(
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self.store.have_seen_events("room1", ["event10", "event19"])
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)
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self.assertEqual(res, {"event10"})
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self.assertEqual(ctx.get_resource_usage().db_txn_count, 0)
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def test_query_via_event_cache(self):
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# fetch an event into the event cache
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self.get_success(self.store.get_event("event10"))
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# looking it up should now cause no db hits
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with LoggingContext(name="test") as ctx:
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res = self.get_success(self.store.have_seen_events("room1", ["event10"]))
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self.assertEqual(res, {"event10"})
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self.assertEqual(ctx.get_resource_usage().db_txn_count, 0)
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class EventCacheTestCase(unittest.HomeserverTestCase):
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"""Test that the various layers of event cache works."""
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servlets = [
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admin.register_servlets,
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room.register_servlets,
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login.register_servlets,
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]
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def prepare(self, reactor, clock, hs):
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self.store: EventsWorkerStore = hs.get_datastores().main
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self.user = self.register_user("user", "pass")
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self.token = self.login(self.user, "pass")
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self.room = self.helper.create_room_as(self.user, tok=self.token)
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res = self.helper.send(self.room, tok=self.token)
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self.event_id = res["event_id"]
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# Reset the event cache so the tests start with it empty
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self.store._get_event_cache.clear()
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def test_simple(self):
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"""Test that we cache events that we pull from the DB."""
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with LoggingContext("test") as ctx:
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self.get_success(self.store.get_event(self.event_id))
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# We should have fetched the event from the DB
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self.assertEqual(ctx.get_resource_usage().evt_db_fetch_count, 1)
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def test_dedupe(self):
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"""Test that if we request the same event multiple times we only pull it
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out once.
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"""
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with LoggingContext("test") as ctx:
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d = yieldable_gather_results(
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self.store.get_event, [self.event_id, self.event_id]
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)
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self.get_success(d)
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# We should have fetched the event from the DB
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self.assertEqual(ctx.get_resource_usage().evt_db_fetch_count, 1)
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class DatabaseOutageTestCase(unittest.HomeserverTestCase):
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"""Test event fetching during a database outage."""
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def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer):
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self.store: EventsWorkerStore = hs.get_datastores().main
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self.room_id = f"!room:{hs.hostname}"
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self.event_ids = [f"event{i}" for i in range(20)]
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self._populate_events()
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def _populate_events(self) -> None:
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"""Ensure that there are test events in the database.
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When testing with the in-memory SQLite database, all the events are lost during
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the simulated outage.
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To ensure consistency between `room_id`s and `event_id`s before and after the
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outage, rows are built and inserted manually.
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Upserts are used to handle the non-SQLite case where events are not lost.
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"""
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self.get_success(
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self.store.db_pool.simple_upsert(
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"rooms",
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{"room_id": self.room_id},
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{"room_version": RoomVersions.V4.identifier},
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)
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)
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self.event_ids = [f"event{i}" for i in range(20)]
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for idx, event_id in enumerate(self.event_ids):
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self.get_success(
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self.store.db_pool.simple_upsert(
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"events",
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{"event_id": event_id},
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{
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"event_id": event_id,
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"room_id": self.room_id,
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"topological_ordering": idx,
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"stream_ordering": idx,
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"type": "test",
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"processed": True,
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"outlier": False,
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},
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)
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)
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self.get_success(
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self.store.db_pool.simple_upsert(
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"event_json",
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{"event_id": event_id},
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{
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"room_id": self.room_id,
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"json": json.dumps({"type": "test", "room_id": self.room_id}),
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"internal_metadata": "{}",
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"format_version": EventFormatVersions.V3,
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},
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)
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)
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@contextmanager
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def _outage(self) -> Generator[None, None, None]:
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"""Simulate a database outage.
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Returns:
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A context manager. While the context is active, any attempts to connect to
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the database will fail.
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"""
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connection_pool = self.store.db_pool._db_pool
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# Close all connections and shut down the database `ThreadPool`.
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connection_pool.close()
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# Restart the database `ThreadPool`.
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connection_pool.start()
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original_connection_factory = connection_pool.connectionFactory
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def connection_factory(_pool: ConnectionPool) -> Connection:
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raise Exception("Could not connect to the database.")
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connection_pool.connectionFactory = connection_factory # type: ignore[assignment]
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try:
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yield
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finally:
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connection_pool.connectionFactory = original_connection_factory
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# If the in-memory SQLite database is being used, all the events are gone.
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# Restore the test data.
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self._populate_events()
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def test_failure(self) -> None:
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"""Test that event fetches do not get stuck during a database outage."""
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with self._outage():
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failure = self.get_failure(
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self.store.get_event(self.event_ids[0]), Exception
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)
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self.assertEqual(str(failure.value), "Could not connect to the database.")
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def test_recovery(self) -> None:
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"""Test that event fetchers recover after a database outage."""
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with self._outage():
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# Kick off a bunch of event fetches but do not pump the reactor
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event_deferreds = []
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for event_id in self.event_ids:
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event_deferreds.append(ensureDeferred(self.store.get_event(event_id)))
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# We should have maxed out on event fetcher threads
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self.assertEqual(self.store._event_fetch_ongoing, EVENT_QUEUE_THREADS)
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# All the event fetchers will fail
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self.pump()
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self.assertEqual(self.store._event_fetch_ongoing, 0)
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for event_deferred in event_deferreds:
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failure = self.get_failure(event_deferred, Exception)
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self.assertEqual(
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str(failure.value), "Could not connect to the database."
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)
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# This next event fetch should succeed
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self.get_success(self.store.get_event(self.event_ids[0]))
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class GetEventCancellationTestCase(unittest.HomeserverTestCase):
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"""Test cancellation of `get_event` calls."""
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servlets = [
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admin.register_servlets,
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room.register_servlets,
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login.register_servlets,
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]
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def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer):
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self.store: EventsWorkerStore = hs.get_datastores().main
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self.user = self.register_user("user", "pass")
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self.token = self.login(self.user, "pass")
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self.room = self.helper.create_room_as(self.user, tok=self.token)
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res = self.helper.send(self.room, tok=self.token)
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self.event_id = res["event_id"]
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# Reset the event cache so the tests start with it empty
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self.store._get_event_cache.clear()
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@contextmanager
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def blocking_get_event_calls(
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self,
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) -> Generator[
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Tuple["Deferred[None]", "Deferred[None]", "Deferred[None]"], None, None
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]:
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"""Starts two concurrent `get_event` calls for the same event.
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Both `get_event` calls will use the same database fetch, which will be blocked
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at the time this function returns.
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Returns:
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A tuple containing:
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* A `Deferred` that unblocks the database fetch.
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* A cancellable `Deferred` for the first `get_event` call.
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* A cancellable `Deferred` for the second `get_event` call.
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"""
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# Patch `DatabasePool.runWithConnection` to block.
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unblock: "Deferred[None]" = Deferred()
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original_runWithConnection = self.store.db_pool.runWithConnection
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async def runWithConnection(*args, **kwargs):
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await unblock
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return await original_runWithConnection(*args, **kwargs)
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with mock.patch.object(
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self.store.db_pool,
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"runWithConnection",
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new=runWithConnection,
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):
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ctx1 = LoggingContext("get_event1")
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ctx2 = LoggingContext("get_event2")
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async def get_event(ctx: LoggingContext) -> None:
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with ctx:
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await self.store.get_event(self.event_id)
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get_event1 = ensureDeferred(get_event(ctx1))
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get_event2 = ensureDeferred(get_event(ctx2))
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# Both `get_event` calls ought to be blocked.
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self.assertNoResult(get_event1)
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self.assertNoResult(get_event2)
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yield unblock, get_event1, get_event2
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# Confirm that the two `get_event` calls shared the same database fetch.
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self.assertEqual(ctx1.get_resource_usage().evt_db_fetch_count, 1)
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self.assertEqual(ctx2.get_resource_usage().evt_db_fetch_count, 0)
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def test_first_get_event_cancelled(self):
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"""Test cancellation of the first `get_event` call sharing a database fetch.
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The first `get_event` call is the one which initiates the fetch. We expect the
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fetch to complete despite the cancellation. Furthermore, the first `get_event`
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call must not abort before the fetch is complete, otherwise the fetch will be
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using a finished logging context.
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"""
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with self.blocking_get_event_calls() as (unblock, get_event1, get_event2):
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# Cancel the first `get_event` call.
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get_event1.cancel()
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# The first `get_event` call must not abort immediately, otherwise its
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# logging context will be finished while it is still in use by the database
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# fetch.
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self.assertNoResult(get_event1)
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# The second `get_event` call must not be cancelled.
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self.assertNoResult(get_event2)
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# Unblock the database fetch.
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unblock.callback(None)
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# A `CancelledError` should be raised out of the first `get_event` call.
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exc = self.get_failure(get_event1, CancelledError).value
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self.assertIsInstance(exc, CancelledError)
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# The second `get_event` call should complete successfully.
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self.get_success(get_event2)
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def test_second_get_event_cancelled(self):
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"""Test cancellation of the second `get_event` call sharing a database fetch."""
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with self.blocking_get_event_calls() as (unblock, get_event1, get_event2):
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# Cancel the second `get_event` call.
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get_event2.cancel()
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# The first `get_event` call must not be cancelled.
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self.assertNoResult(get_event1)
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# The second `get_event` call gets cancelled immediately.
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exc = self.get_failure(get_event2, CancelledError).value
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self.assertIsInstance(exc, CancelledError)
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# Unblock the database fetch.
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unblock.callback(None)
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# The first `get_event` call should complete successfully.
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self.get_success(get_event1)
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