Re: poor cpu utilization on dual cpu box

The suggestion that we are saturating the memory bus
makes a lot of sense.  We originally started with a
low setting for shared buffers and resized it to fit
all our tables (since we have memory to burn). That
improved stand alone performance but not concurrent
performance - this would explain that phenomenon
somewhat.

Will investigate further down this track.

Thanks to everyone who responded!

Cheers,

Simon.

Josh Berkus <josh@agliodbs.com> wrote:Simon,

> The issue is that no matter how much query load we
throw at our server it
> seems almost impossible to get it to utilize more
than 50% cpu on a
> dual-cpu box. For a single connection we can use all
of one CPU, but
> multiple connections fail to increase the overall
utilization (although
> they do cause it to spread across CPUs).

This is perfectly normal. It's a rare x86 machine
(read fiber channel) where
you don't saturate the I/O or the RAM *long* before
you saturate the CPU.
Transactional databases are an I/O intensive
operation, not a CPU-intensive
one.

> We are running with shared buffers large enough to
hold the
> entire database

Which is bad. This is not what shared buffers are for.
See:
http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html

--
Josh Berkus
Aglio Database Solutions
San Francisco

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