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From:Walter Heck - OlinData.com Date:April 1 2009 12:45am
Subject:Re: Joining memory tables is very very slow!
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Memory tables use hash indexes by default instead of b-tree. Try
changing the index, that should help significantly.

regards,

Walter

On Tue, Mar 31, 2009 at 6:47 PM, mos <mos99@stripped> wrote:
> I'm using MySQL 5.1.30 and have several memory tables with indexes on the
> appropriate columns. When I try and join 2 particular memory tables together
> to get 5k rows, it takes 90 seconds.
> This is incredibly slow considering table1 has 11k rows and table2 has 5k
> rows. A table join like this should take 10 ms.
>
> An explain shows it is not using and index for the table but Extra has
> "Using where;Using join buffer". I can try and use "Force Index(..)" and it
> still will not use the index.
>
> If I use the MyISAM table instead of that one particular memory table the
> query takes 800ms which is reasonably fast.
>
> Is there a way to force it not to use the join buffer?
> Has anyone else noticed the slow memory table joins in 5.1?
>
> TIA
> Mike
>
>
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Thread
Joining memory tables is very very slow!mos31 Mar
  • Re: Joining memory tables is very very slow!Walter Heck - OlinData.com1 Apr
  • Re: Joining memory tables is very very slow!Virgilio Quilario1 Apr