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Why can 'query end' thread state take long time?

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  • Why can 'query end' thread state take long time?

    Hi,
    Threads can leave in 'query end' state for seconds.

    Percona 5.5.16
    Centos 6

  • #2
    That could happen when the system stalls. The cause could be a checkpoint flushing storm, or contention on query cache, or other reasons.

    For innodb flushing storm, you can read about it from these blog posts :
    http://www.mysqlperformanceblog.com/...and-solutions/
    http://www.mysqlperformanceblog.com/...-5-5-flushing/

    Percona 5.5 has improvements in stabilize IO and flushing activity. The related variables are talked about here:
    http://www.percona.com/doc/percona-s...odb_io_55.html

    For query cache, you may check global status Qcache_% to see the usage info, and use Qcache_hits / (Com_select + Qcache_hits) x 100 to check efficiency. For most write heavy workload, it is better to disable query cache for improved overall performance.

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