Re: Solaris shared_buffers anomaly?

On Tue, Jun 13, 2006 at 03:21:34PM -0700, Mischa Sandberg wrote:
> Jim C. Nasby wrote:
> ...
> >Actually, in 8.1.x I've seen some big wins from greatly increasing the
> >amount of shared_buffers, even as high as 50% of memory, thanks to the
> >changes made to the buffer management code. ...
>
> Anyone else run into a gotcha that one of our customers ran into?
> PG 7.4.8 running on Solaris 2.6, USparc w 4GB RAM.
> Usually about 50 active backends.
> (No reason to believe this wouldn't apply to 8.x).
>
> Initially shared_buffers were set to 1000 (8MB).
> Then, we moved all apps but the database server off the box.
>
> Raised shared_buffers to 2000 (16MB).
> Modest improvement in some frequent repeated queries.
>
> Raised shared_buffers to 16000 (128MB).
> DB server dropped to a CRAWL.
>
> vmstat showed that it was swapping like crazy.
> Dropped shared_buffers back down again.
> Swapping stopped.

What's sort_mem set to? I suspect you simply ran the machine out of
memory.

Also, Solaris by default will only use a portion of memory for
filesystem caching, which will kill PostgreSQL performance.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461