MySQL replication - invalidating query cache entries (table) We lately moved to MySQL V5.5 on CentOS release 6.7 with master and 2 slaves. Since then the replication process lags a lot behind the master with the line in the process list of:


  invalidating query cache entries (table).


The global query_cache_type &amp; size were set to 0.

I have checked around and I can see it's a known old bug in MySQL but could not find a workaround for this issue.

Any advice?


query_cache_type OFF in my.cnf before server restart.
query_cache_wlock_invalidate set to OFF.
using default % storage_engine as InnoDB.


We ran some more tests and we had an issue with disk IO - sar -u showed about 3-4 %iowait, disks infra changes help reduce this to about 1.5-2% but it still doesn't help the replication not lagging for 5000(!) seconds behind the master.
Was query_cache_type OFF (0) in my.cnf, not merely turned off later?  (This seems to be critical for having it really off.)
Another possible common thread in the bugs -- MyISAM.  If you are using MyISAM, you really should convert to InnoDB.  There are many reasons for converting.  Here are some tips on doing the conversion:  http://mysql.rjweb.org/doc.php/myisam2innodb
Make sure that query_cache_wlock_invalidate is OFF.