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Bug #51391 Deadlock involving events during rqg_info_schema test

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This was a deadlock between CREATE/ALTER/DROP EVENT and a query
accessing both the mysql.event table and I_S.GLOBAL_VARIABLES.

The root of the problem was that the LOCK_event_metadata mutex was
used to both protect the "event_scheduler" global system variable
and the internal event data structures used by CREATE/ALTER/DROP EVENT.

The deadlock would occur if CREATE/ALTER/DROP EVENT held
LOCK_event_metadata while trying to open the mysql.event table,
at the same time as the query had mysql.event open, trying to
lock LOCK_event_metadata to access "event_scheduler".

This bug was fixed in the scope of Bug#51160 by using only
LOCK_global_system_variables to protect "event_scheduler".
This makes it so that the query above won't lock LOCK_event_metadata,
thereby preventing this deadlock from occuring.

This patch contains no code changes.
Test case added to lock_sync.test.
This commit is contained in:
Jon Olav Hauglid
2010-04-15 14:14:28 +02:00
parent 48ac4ff51f
commit 4347e302a8
2 changed files with 53 additions and 0 deletions
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20
mysql-test/r/lock_sync.result
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@ -92,3 +92,23 @@ COMMIT;
# Connection default
# Reaping ALTER TABLE t1 ADD COLUMN j INT
DROP TABLE t1, t2;
#
# Bug#51391 Deadlock involving events during rqg_info_schema test
#
CREATE EVENT e1 ON SCHEDULE EVERY 5 HOUR DO SELECT 1;
CREATE EVENT e2 ON SCHEDULE EVERY 5 HOUR DO SELECT 2;
# Connection con1
SET DEBUG_SYNC="before_lock_tables_takes_lock SIGNAL drop WAIT_FOR query";
# Sending:
DROP EVENT e1;;
# Connection default
SET DEBUG_SYNC="now WAIT_FOR drop";
SELECT name FROM mysql.event, INFORMATION_SCHEMA.GLOBAL_VARIABLES
WHERE definer = VARIABLE_VALUE;
name
SET DEBUG_SYNC="now SIGNAL query";
# Connection con1
# Reaping: DROP EVENT t1
# Connection default
DROP EVENT e2;
SET DEBUG_SYNC="RESET";