Re: How to determine if my setting for shared_buffers is too high?

Remember that as you increase shared_buffers you might need to make the
bgwriter more aggressive too.

On Thu, Dec 07, 2006 at 11:42:39AM -0500, Bill Moran wrote:
>
> I'm gearing up to do some serious investigation into performance for
> PostgreSQL with regard to our application. I have two issues that I've
> questions about, and I'll address them in two seperate emails.
>
> This one regards tuning shared_buffers.
>
> I believe I have a good way to monitor database activity and tell when
> a database grows large enough that it would benefit from more
> shared_buffers: if I monitor the blks_read column of pg_stat_database,
> it should increase very slowly if there is enough shared_buffer
> space. When shared buffer space runs out, more disk read requests
> will be required and this number will begin to climb.
>
> If anyone sees a flaw in this approach, I'd be interested to hear it.
>
> The other tuning issue with shared_buffers is how to tell if I'm
> allocating too much. For example, if I allocate 1G of RAM to
> shared buffers, and the entire database can fit in 100M, that 900M
> might be better used as work_mem, or something else.
>
> I haven't been able to find anything regarding how much of the
> shared buffer space PostgreSQL is actually using, as opposed to
> simply allocating.
>
> --
> Bill Moran
> Collaborative Fusion Inc.
>
> wmoran(at)collaborativefusion(dot)com
> Phone: 412-422-3463x4023
>
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> TIP 5: don't forget to increase your free space map settings
>

--
Jim Nasby jim(at)nasby(dot)net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)