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MDEV-8302: Duplicate key with parallel replication

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This bug is essentially another variant of MDEV-7458.

If a transaction conflict caused a deadlock kill of T2 in record_gtid()
during commit, the code would do a rollback _before_ running
rgi->unmark_start_commit(). This creates a race where following transactions
could start too early (before T2 has completed its transaction retry). This
in turn could lead to replication failure, if there was a conflict that
caused eg. duplicate key error or similar.

The fix is to remove these rollbacks (in Query_log_event::do_apply_event()
and Xid_log_event::do_apply_event(). They seem out-of-place; code in
log_event.cc generally does not roll back on error, this is handled higher
up.

In addition, because of the extreme difficulty of reproducing bugs like
MDEV-7458 and MDEV-8302, this patch adds some extra precations to try to
detect (in debug builds) or prevent (in release builds) similar bugs.
ha_rollback_trans() will now call unmark_start_commit() if needed (and
assert in debug build when a caller does rollback without unmark first).

We also add an extra check for thd->killed() so that we avoid doing
mark_start_commit() if we already have a pending deadlock kill.

And we add a missing unmark_start_commit() call in the error case, found by
the above assertion.
This commit is contained in:
Kristian Nielsen
2015-08-04 11:20:03 +02:00
parent a6087e7dc1
commit 9b9c5e890c
5 changed files with 147 additions and 6 deletions
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40
mysql-test/suite/rpl/r/rpl_parallel.result
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@@ -1649,6 +1649,46 @@ include/stop_slave.inc
SET GLOBAL debug_dbug= @old_debg;
SET GLOBAL max_relay_log_size= @old_max;
include/start_slave.inc
*** MDEV-8302: Duplicate key with parallel replication ***
include/stop_slave.inc
/* Inject a small sleep which makes the race easier to hit. */
SET @old_dbug=@@GLOBAL.debug_dbug;
SET GLOBAL debug_dbug="+d,inject_mdev8302";
INSERT INTO t7 VALUES (100,1), (101,2), (102,3), (103,4), (104,5);
SET @old_dbug= @@SESSION.debug_dbug;
SET @commit_id= 20000;
SET SESSION debug_dbug="+d,binlog_force_commit_id";
SET SESSION debug_dbug=@old_dbug;
SELECT * FROM t7 ORDER BY a;
a b
1 1
2 2
3 86
4 4
5 5
100 5
101 1
102 2
103 3
104 4
include/save_master_gtid.inc
include/start_slave.inc
include/sync_with_master_gtid.inc
SELECT * FROM t7 ORDER BY a;
a b
1 1
2 2
3 86
4 4
5 5
100 5
101 1
102 2
103 3
104 4
include/stop_slave.inc
SET GLOBAL debug_dbug=@old_dbug;
include/start_slave.inc
include/stop_slave.inc
SET GLOBAL slave_parallel_threads=@old_parallel_threads;
include/start_slave.inc