[rt-users] mysqltuner: temp tables & table cache hit rate?

Kenneth Marshall ktm at rice.edu
Tue Apr 7 16:54:24 EDT 2009

On Tue, Apr 07, 2009 at 01:50:26PM -0700, Paul Hirose wrote:
> Since I started RT, I've always gotten these three comments from mysqltuner
> [!!] Temporary tables created on disk: 30% (354 on disk / 1K total)
> [!!] Table cache hit rate: 18% (40 open / 222 opened)
> General recommendations:
>      Reduce your SELECT DISTINCT queries without LIMIT clauses
> Is there a way to help the above metrics and reduce the select disticnt queries thing?  Are these code-level changes or just more/better usage by our staff?  If it's a usage thing, what things should we stop doing and what should we start doing?
> If the answer is to have better/more index in MySQL (a recommendation I've seen many times on this list), could you please also include a recommendation on the index itself?  I don't know what indexes to create.
> RT382, MySQL 5.077, Apache 2.2.11, mod-perl 2.04, mysqltuner 1.00, OpenBSD 4.4-STABLE, 2.5GB RAM, 3GB swap.  Machine dedicated to RT.
> Thank you,
> PH


You are getting those results because RT runs many different queries
and uses DISTINCT a lot to prevent duplicate rows. There is nothing to
be done, these output of mysqltuner just gives you places to look for
obvious problems. This is not one for RT.


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