Fix rare deadlock when using read/write locks (#16133)

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Erik Johnston 2023-08-23 13:45:25 +01:00 committed by GitHub
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commit 4adaba9acf
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changelog.d/16133.bugfix Normal file
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Fix a rare race that could block new events from being sent for up to two minutes. Introduced in v1.90.0.

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/* Copyright 2023 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.
*/
-- To avoid the possibility of a deadlock, lock the
-- `worker_read_write_locks_mode` table so that we serialize inserts/deletes
-- for a specific lock name/key.
CREATE OR REPLACE FUNCTION delete_read_write_lock_parent_before() RETURNS trigger AS $$
BEGIN
-- `PERFORM` is a `SELECT` which discards the rows.
PERFORM * FROM worker_read_write_locks_mode
WHERE
lock_name = OLD.lock_name
AND lock_key = OLD.lock_key
FOR UPDATE;
RETURN OLD;
END
$$
LANGUAGE plpgsql;
DROP TRIGGER IF EXISTS delete_read_write_lock_parent_before_trigger ON worker_read_write_locks;
CREATE TRIGGER delete_read_write_lock_parent_before_trigger BEFORE DELETE ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE delete_read_write_lock_parent_before();