From f112cfe5bb2c918c9e942941686a05664d8bd7da Mon Sep 17 00:00:00 2001 From: Erik Johnston Date: Thu, 24 Sep 2020 16:53:51 +0100 Subject: Fix MultiWriteIdGenerator's handling of restarts. (#8374) On startup `MultiWriteIdGenerator` fetches the maximum stream ID for each instance from the table and uses that as its initial "current position" for each writer. This is problematic as a) it involves either a scan of events table or an index (neither of which is ideal), and b) if rows are being persisted out of order elsewhere while the process restarts then using the maximum stream ID is not correct. This could theoretically lead to race conditions where e.g. events that are persisted out of order are not sent down sync streams. We fix this by creating a new table that tracks the current positions of each writer to the stream, and update it each time we finish persisting a new entry. This is a relatively small overhead when persisting events. However for the cache invalidation stream this is a much bigger relative overhead, so instead we note that for invalidation we don't actually care about reliability over restarts (as there's no caches to invalidate) and simply don't bother reading and writing to the new table in that particular case. --- synapse/storage/databases/main/__init__.py | 8 +++++++- synapse/storage/databases/main/events_worker.py | 4 ++++ .../main/schema/delta/58/18stream_positions.sql | 22 ++++++++++++++++++++++ 3 files changed, 33 insertions(+), 1 deletion(-) create mode 100644 synapse/storage/databases/main/schema/delta/58/18stream_positions.sql (limited to 'synapse/storage/databases') diff --git a/synapse/storage/databases/main/__init__.py b/synapse/storage/databases/main/__init__.py index ccb3384db9..0cb12f4c61 100644 --- a/synapse/storage/databases/main/__init__.py +++ b/synapse/storage/databases/main/__init__.py @@ -160,14 +160,20 @@ class DataStore( ) if isinstance(self.database_engine, PostgresEngine): + # We set the `writers` to an empty list here as we don't care about + # missing updates over restarts, as we'll not have anything in our + # caches to invalidate. (This reduces the amount of writes to the DB + # that happen). self._cache_id_gen = MultiWriterIdGenerator( db_conn, database, - instance_name="master", + stream_name="caches", + instance_name=hs.get_instance_name(), table="cache_invalidation_stream_by_instance", instance_column="instance_name", id_column="stream_id", sequence_name="cache_invalidation_stream_seq", + writers=[], ) else: self._cache_id_gen = None diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py index de9e8d1dc6..f95679ebc4 100644 --- a/synapse/storage/databases/main/events_worker.py +++ b/synapse/storage/databases/main/events_worker.py @@ -83,21 +83,25 @@ class EventsWorkerStore(SQLBaseStore): self._stream_id_gen = MultiWriterIdGenerator( db_conn=db_conn, db=database, + stream_name="events", instance_name=hs.get_instance_name(), table="events", instance_column="instance_name", id_column="stream_ordering", sequence_name="events_stream_seq", + writers=hs.config.worker.writers.events, ) self._backfill_id_gen = MultiWriterIdGenerator( db_conn=db_conn, db=database, + stream_name="backfill", instance_name=hs.get_instance_name(), table="events", instance_column="instance_name", id_column="stream_ordering", sequence_name="events_backfill_stream_seq", positive=False, + writers=hs.config.worker.writers.events, ) else: # We shouldn't be running in worker mode with SQLite, but its useful diff --git a/synapse/storage/databases/main/schema/delta/58/18stream_positions.sql b/synapse/storage/databases/main/schema/delta/58/18stream_positions.sql new file mode 100644 index 0000000000..985fd949a2 --- /dev/null +++ b/synapse/storage/databases/main/schema/delta/58/18stream_positions.sql @@ -0,0 +1,22 @@ +/* Copyright 2020 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. + */ + +CREATE TABLE stream_positions ( + stream_name TEXT NOT NULL, + instance_name TEXT NOT NULL, + stream_id BIGINT NOT NULL +); + +CREATE UNIQUE INDEX stream_positions_idx ON stream_positions(stream_name, instance_name); -- cgit 1.4.1