MySQL Query Cache Fragmentation Slows Down the Server
Last updated on NOVEMBER 24, 2016
Applies to:MySQL Server - Version 4.0 to 5.5 [Release 4.0 to 5.5]
Information in this document applies to any platform.
If you use InnoDB, the InnoDB status seems frozen for 10 or more seconds, even minutes.
Many thread states are Query Cache related such as
- freeing items
- storing result in query cache
MySQL thread id 486210, query id 130927562 freeing items
SELECT * FROM dual
The SQL query profile shows CPU only queries and the CPU usage on one core is high, while others may be very low.
On Linux, the PMP (Poor's Man Profiler) output, (see http://poormansprofiler.org) shows that the Query Cache thread is busy freeing memory blocks.
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