Re: PrivateRefCount (for 8.3)

NikhilS <nikkhils(at)gmail(dot)com> writes:
> What is the opinion of the list as to the best way of measuring if the
> following implementation is ok?
> http://archives.postgresql.org/pgsql-hackers/2007-01/msg00752.php
> As mentioned in earlier mails, this will reduce the per-backend usage of
> memory by an amount which will be a fraction (single digit percentage)
> of (NBuffers
> * int) size. I have done pgbench/dbt2 runs and I do not see any negative
> impact because of this.

I find it extremely telling that you don't claim to have seen any
positive impact either.

I think that the original argument
http://archives.postgresql.org/pgsql-hackers/2006-11/msg00797.php
is basically bogus. At 500000 buffers (4GB in shared memory) the
per-backend space for PrivateRefCount is still only 2MB, which is
simply not as significant as Simon claims; a backend needs at least
that much for catalog caches etc. There is, furthermore, no evidence
that running shared_buffers that high is a good idea in the first
place, or that there aren't other performance bottlenecks that will
manifest before this one becomes interesting.

My inclination is to keep it simple until there's some real evidence
of a problem and benefit.

regards, tom lane