Re: [PATCHES] ARC Memory Usage analysis

On Tue, 2004-10-26 at 06:53, Tom Lane wrote:
> Greg Stark <gsstark(at)mit(dot)edu> writes:
> > Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> >> Another issue is what we do with the effective_cache_size value once we
> >> have a number we trust. We can't readily change the size of the ARC
> >> lists on the fly.
>
> > Huh? I thought effective_cache_size was just used as an factor the cost
> > estimation equation.
>
> Today, that is true. Jan is speculating about using it as a parameter
> of the ARC cache management algorithm ... and that worries me.
>

ISTM that we should be optimizing the use of shared_buffers, not whats
outside. Didn't you (Tom) already say that?

BTW, very good ideas on how to proceed, but why bother?

For me, if the sysadmin didn't give shared_buffers to PostgreSQL, its
because the memory is intended for use by something else and so not
available at all. At least not dependably. The argument against large
shared_buffers because of swapping applies to that assumption also...the
OS cache is too volatile to attempt to gauge sensibly.

There's an argument for improving performance for people that haven't
set their parameters correctly, but thats got to be a secondary
consideration anyhow.

--
Best Regards, Simon Riggs