Re: Shared buffers vs large files

On Fri, 2002-03-01 at 18:57, Glen Parker wrote:
> > shared_buffers at 4096 (32MB if my calculations are correct),
> > sort_mem = 65536 # min 32
> > vacuum_mem = 16384 # min 1024
> >
> > The machine has 1GB of ram.
> >
> > I don't expect to have more than a handfull of connections at a time (from
> > 1 to 10). Should I increate the shared buffers to 64MB? 128MB?
>
> On a 1GB machine (still PG 7.1.3) I'm currently running:
>
> shared_buffers: 48000 (about 400MB)
> sort_mem: 8192
>
> I haven't done much testing with sort_mem values, but...
>
> This is very very VERY unscientific, but I haven't seen a shared_buffers
> value that is so big that it seems to hurt performance (unless it causes
> swapping obviously), and my installation is dedicated to postgres so I don't
> need the memory for much of anything else.

Keep in mind that this memory is allocated by Postgres on postmaster
startup. Thus, the kernel can't use it for I/O buffers. Depending on
what UNIX variant you're running and the kind of load the box is under,
setting shared_buffers that high may or may not be a performance win.

However, I agree with you in principle: for a production PostgreSQL
server, the default shared_buffers settings are ridiculously small.

Another parameter to consider increasing is wal_buffers; in my
experience that can improve performance as well.

Cheers,

Neil

--
Neil Conway <neilconway(at)rogers(dot)com>
PGP Key ID: DB3C29FC