Re: Performance for seq. scans

> From: Jules Bean <jules(at)jellybean(dot)co(dot)uk>
> To: pgsql-general(at)postgresql(dot)org
> Subject: Performance for seq. scans
>
> I've had a look over the docs and the FAQ and I can't see anything
> answering this, so here goes:
>
> I'm in the (slightly unusual, in a relational world) situation that
> the dominant query on my database is a wildcard search, so that no
> indexes can be used. (E.g. select * from table_a where foo like
> '%bar%').
>
> Interestingly, using 'vmstat' shows that the CPU is maxxed out at 50%
> (this being a dual CPU machine), while the disk access is a mere
> 4M/sec --- bonnie claims this machine is capable of around 25M/sec to
> this particular disk. So it would seem that the bottleneck is the
> CPU. [I understand why both CPUs aren't used]

I'd make sure that you're using the latest compilers to build
postgres, and maxing-out the optimization. If you're binaries are
unoptimized, that ought to be good for 15% (for your app, possibly
more).

Also, you haven't said what postmaster options you're using - I've
seen big changes by tweaking sort memory, buffer pools, etc. Details
of the parameters are in the man pages and docs.

-- Mike