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  1. #1
    Join Date
    Mar 2011
    Posts
    393

    join_buffer_size

    This was the diagnostic result from tuning primer and it has me confused. Should i be lowering the join_buffer_size?

    JOINS
    Current join_buffer_size = 6.00 M
    You have had 0 queries where a join could not use an index properly
    Your joins seem to be using indexes properly
    join_buffer_size >= 4 M
    This is not advised

  2. #2
    Join Date
    Aug 2002
    Location
    Milton Keynes
    Posts
    352
    Most database workloads can cope well with a very small join buffer size, I would recommend reducing it to 1MB or 512kb and giving it a week to see if you need bigger (or indeed could cope with smaller).

    Remember - this is a per-thread and per-join buffer, so a query with 4 joins will cause the thread to allocate 24mb, in most cases only a small amount of the allocated buffer will be used.

    Somebody wrote a nice article discussing join buffer size: http://www.mysqlperformanceblog.com/...ize-allocated/

  3. #3
    Join Date
    Mar 2011
    Posts
    393
    I tried it, observed for few weeks. Gradually raised it back to 4M. Still says
    Join_buffer_size > 4M
    This is not advised.

    On one hand it says raise it on the other it advices against it??

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