replicate FLUSH QUERY CACHE command

[Seppo Jaakola]

wsrep cluster supports query cache (QC) currently. However, the cache will be node local, each node maintains his own cache.
If application is using QC, there may be need to flush/freset the cache at some point.

Therefore the commands: FLUSH QUERY CACHE and RESET QUERY CACHE should be replicated to the cluster, to make sure that no old cached results will be returned to clients.

This can be implemented as TOI operation, although less synchronous implementation would be fine for this purpose as well.

[Nirbhay Choubey (nirbhay)]

"RESET" commands for some reason are never written to the binary log :
..
  case SQLCOM_RESET:
    /*
      RESET commands are never written to the binary log, so we have to
      initialize this variable because RESET shares the same code as FLUSH
    */
    lex->no_write_to_binlog= 1;
   /* fallthrough */
    case SQLCOM_FLUSH:
..

[Nilnandan Joshi (nilnandan-joshi)]

Verified with PXC 5.5 and 5.6. FLUSH QUERY CACHE is written in binlog but not RESET QUERY CACHE.

[root@percona-pxc55-1 ~]# mysql -uroot -p
Enter password:
...
mysql> create table nil (id int, name varchar(10));
Query OK, 0 rows affected (0.07 sec)

mysql> FLUSH QUERY CACHE;
Query OK, 0 rows affected (0.00 sec)

mysql> RESET QUERY CACHE;
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye
[root@percona-pxc55-1 ~]#

[root@percona-pxc55-1 mysql]# mysqlbinlog mysql-bin.000018
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=1*/;
/*!40019 SET @@session.max_insert_delayed_threads=0*/;
/*!50003 SET @OLD_COMPLETION_TYPE=@@COMPLETION_TYPE,COMPLETION_TYPE=0*/;
DELIMITER /*!*/;
# at 4
#140821 19:14:30 server id 3 end_log_pos 107 Start: binlog v 4, server v 5.5.37-35.0-55-log created 140821 19:14:30 at startup
...
# at 280
#140821 19:16:52 server id 3 end_log_pos 386 Query thread_id=5 exec_time=0 error_code=0
SET TIMESTAMP=1408628812/*!*/;
SET @@session.auto_increment_increment=1, @@session.auto_increment_offset=1/*!*/;
create table nil (id int, name varchar(10))
/*!*/;
# at 386
#140821 19:17:14 server id 3 end_log_pos 471 Query thread_id=5 exec_time=0 error_code=0
SET TIMESTAMP=1408628834/*!*/;
SET @@session.auto_increment_increment=2, @@session.auto_increment_offset=2/*!*/;
FLUSH QUERY CACHE
/*!*/;
DELIMITER ;
# End of log file
ROLLBACK /* added by mysqlbinlog */;
/*!50003 SET COMPLETION_TYPE=@OLD_COMPLETION_TYPE*/;
/*!50530 SET @@SESSION.PSEUDO_SLAVE_MODE=0*/;
[root@percona-pxc55-1 mysql]#

[Philip Stoev (philip-stoev-f)]

https://bugs.launchpad.net/codership-mysql/+bug/1376692

[Krunal Bauskar (krunal-bauskar)]

This is solved in latest 5.6. Please refresh.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXC-1110