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MDEV-21953 deadlock between BACKUP STAGE BLOCK_COMMIT and parallel repl.

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The issue was:
T1, a parallel slave worker thread, is waiting for another worker thread to
commit. While waiting, it has the MDL_BACKUP_COMMIT lock.
T2, working for mariabackup, is doing BACKUP STAGE BLOCK_COMMIT and blocks
all commits.
This causes a deadlock as the thread T1 is waiting for can't commit.

Fixed by moving locking of MDL_BACKUP_COMMIT from ha_commit_trans() to
commit_one_phase_2()

Other things:
- Added a new argument to ha_comit_one_phase() to signal if the
  transaction was a write transaction.
- Ensured that ha_maria::implicit_commit() is always called under
  MDL_BACKUP_COMMIT. This code is not needed in 10.5
- Ensure that MDL_Request values 'type' and 'ticket' are always
  initialized. This makes it easier to check the state of the MDL_Request.
- Moved thd->store_globals() earlier in handle_rpl_parallel_thread() as
  thd->init_for_queries() could use a MDL that could crash if store_globals
  where not called.
- Don't call ha_enable_transactions() in THD::init_for_queries() as this
  is both slow (uses MDL locks) and not needed.
This commit is contained in:
Monty
2020-07-20 15:19:25 +03:00
parent c4d5b6b157
commit fc48c8ff4c
11 changed files with 210 additions and 59 deletions
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40
mysql-test/suite/rpl/r/parallel_backup.result Normal file
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include/master-slave.inc
[connection master]
#
# MDEV-21953: deadlock between BACKUP STAGE BLOCK_COMMIT and parallel
# replication
#
connection master;
CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE = innodb;
connection slave;
include/stop_slave.inc
SET @old_parallel_threads= @@GLOBAL.slave_parallel_threads;
SET @old_parallel_mode = @@GLOBAL.slave_parallel_mode;
SET @@global.slave_parallel_threads= 2;
SET @@global.slave_parallel_mode = 'optimistic';
connection master;
INSERT INTO t1 VALUES (1);
INSERT INTO t1 VALUES (2);
connect aux_slave,127.0.0.1,root,,test,$SLAVE_MYPORT,;
BEGIN;
INSERT INTO t1 VALUES (1);
connection slave;
include/start_slave.inc
connection aux_slave;
connect backup_slave,127.0.0.1,root,,test,$SLAVE_MYPORT,;
BACKUP STAGE START;
BACKUP STAGE BLOCK_COMMIT;
connection aux_slave;
ROLLBACK;
connection backup_slave;
BACKUP STAGE END;
connection slave;
include/diff_tables.inc [master:t1,slave:t1]
connection slave;
include/stop_slave.inc
SET @@global.slave_parallel_threads= @old_parallel_threads;
SET @@global.slave_parallel_mode = @old_parallel_mode;
include/start_slave.inc
connection server_1;
DROP TABLE t1;
include/rpl_end.inc