Re: Starting PostgreSQL 8.0.4 with more memory [FreeBSD

On Mon, Oct 31, 2005 at 01:34:12PM +0000, Simon Riggs wrote:
> > Secondly, you're assuming that PostgreSQLs caching is at least as
> > efficient as the OS caching, which is more of an assertion than
> > anything else.
>
> Do you doubt that? Why would shared_buffers be variable otherwise?

Because the optimal hasn't been found and is probably different for
each machine.

There have been tests that demonstrate that you can raise the buffers
to a certain point which is optimal and after that it just doesn't
help [1]. They peg optimal size at 5-10% of memory.

Also, as Tom pointed out, any memory assigned to shared buffers can't
be used for sorts, temporary tables, plain old disk caching, trigger
queues or anything else that isn't shared between backends. There are
far more useful uses of memory than just buffering disk blocks.

Have a nice day,

[1] http://archives.postgresql.org/pgsql-performance/2004-10/msg00110.php
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.