Re: Kernel cache vs shared_buffers

On Sat, May 12, 2007 at 03:28:45PM +0100, Heikki Linnakangas wrote:
> >In the case of it being disk-block based, my
> >inclination would be to let the kernel do the buffering. In the case of
> >the cache being table-row-based, I would expect it to be much more
> >space-efficient and I would be inclined to give the memory to the pg.
> >In that case, is it feasible to set shared_buffers to something like
> >500000 x 8k blocks? We make extensive use of indexes on the larger
> >tables and would seldom, if ever, do sequential scans.
>
> A common rule of thumb people quote here is to set shared_buffers to 1/4
> of available RAM, and leave the rest for OS cache. That's probably a
> good configuration to start with.

If you really care about performance it would be a good idea to start
with that and do your own benchmarking. Much of the consensus about
shared_buffers was built up before 8.0, and the shared buffer management
we have today looks nothing like what was in 7.4. You might find that
shared_buffers = 50% of memory or even higher might perform better for
your workload.

If you do find results like that, please share them. :)
--
Jim Nasby jim(at)nasby(dot)net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)