anonymousland-synapse/synapse/storage/schema/main/delta/59/15locks.sql
Erik Johnston 85d237eba7
Add a distributed lock (#10269)
This adds a simple best effort locking mechanism that works cross workers.
2021-06-29 19:15:47 +01:00

38 lines
1.6 KiB
SQL

/* Copyright 2021 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.
*/
-- A noddy implementation of a distributed lock across workers. While a worker
-- has taken a lock out they should regularly update the `last_renewed_ts`
-- column, a lock will be considered dropped if `last_renewed_ts` is from ages
-- ago.
CREATE TABLE worker_locks (
lock_name TEXT NOT NULL,
lock_key TEXT NOT NULL,
-- We write the instance name to ease manual debugging, we don't ever read
-- from it.
-- Note: instance names aren't guarenteed to be unique.
instance_name TEXT NOT NULL,
-- A random string generated each time an instance takes out a lock. Used by
-- the instance to tell whether the lock is still held by it (e.g. in the
-- case where the process stalls for a long time the lock may time out and
-- be taken out by another instance, at which point the original instance
-- can tell it no longer holds the lock as the tokens no longer match).
token TEXT NOT NULL,
last_renewed_ts BIGINT NOT NULL
);
CREATE UNIQUE INDEX worker_locks_key ON worker_locks (lock_name, lock_key);