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Mysql high IO usage

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  • Mysql high IO usage

    Hi,

    We have not small database (~450Gb, ~30000 tables) and few slave servers for it:
    - slave2 (scsi hdd with raid 10)
    - slave3 (sas hdd wthout raid)
    but after we doing "optimize" at master server replication at slave3 starts to lag:
    1. load on the disk becomes 100%
    2. the number of inserts falls
    3. lag continues to grow

    It seems to be a hardware problem, but if we will get a new copy of Mysql datadir from slave2 (which have no lag) to slave3 - we will get an actual copy of database (when it will catch up). On graphs in cacti we can see that hardware can handle ~100 inserts per second, but when it's 100% IO - there is only ~30 inserts per second.

    What we alredy did:
    1. Move relay logs to another hdd
    2. disable journal at ext4 and tune it a little (mount opts - rw,noatime,nodiratime,data=writeback)

    but no improvement...

    What else to tune?

  • #2
    is this problem appears during optimize replicates to slave and optimize is in progress or optimize completed on both master/slave and slave catches up master??
    In first case you can run optimize on master ( do not replicate session commands "set sql_log_bin=0" ) and then on slave, in this case your slave will not lag during optimize.

    Comment


    • #3
      Hi,

      I would suggest to read this blog post. http://www.mysqlperformanceblog.com/...-optimization/

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