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72 lines
2.6 KiB
Plaintext
72 lines
2.6 KiB
Plaintext
/* Copyright 2023 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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*/
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-- Remove a previous attempt to avoid deadlocks
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DROP TRIGGER IF EXISTS delete_read_write_lock_parent_before_trigger ON worker_read_write_locks;
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DROP FUNCTION IF EXISTS delete_read_write_lock_parent_before;
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-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
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-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
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-- update the `worker_read_write_locks_mode.token` to match another instance
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-- that has currently acquired the lock, or we delete the row if nobody has
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-- currently acquired a lock.
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CREATE OR REPLACE FUNCTION delete_read_write_lock_parent() RETURNS trigger AS $$
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DECLARE
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new_token TEXT;
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mode_row_token TEXT;
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BEGIN
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-- Only update the token in `_mode` if its our token. This prevents
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-- deadlocks.
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--
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-- We shove the token into `mode_row_token`, as otherwise postgres complains
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-- we're not using the returned data.
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SELECT token INTO mode_row_token FROM worker_read_write_locks_mode
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WHERE
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lock_name = OLD.lock_name
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AND lock_key = OLD.lock_key
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AND token = OLD.token
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FOR UPDATE;
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IF NOT FOUND THEN
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RETURN NEW;
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END IF;
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SELECT token INTO new_token FROM worker_read_write_locks
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WHERE
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lock_name = OLD.lock_name
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AND lock_key = OLD.lock_key
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LIMIT 1 FOR UPDATE SKIP LOCKED;
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IF NOT FOUND THEN
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DELETE FROM worker_read_write_locks_mode
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WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key AND token = OLD.token;
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ELSE
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UPDATE worker_read_write_locks_mode
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SET token = new_token
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WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
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END IF;
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RETURN NEW;
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END
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$$
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LANGUAGE plpgsql;
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DROP TRIGGER IF EXISTS delete_read_write_lock_parent_trigger ON worker_read_write_locks;
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CREATE TRIGGER delete_read_write_lock_parent_trigger AFTER DELETE ON worker_read_write_locks
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FOR EACH ROW
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EXECUTE PROCEDURE delete_read_write_lock_parent();
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