Re: autovacuum maintenance_work_mem

On 11/16/10 9:27 AM, Robert Haas wrote:
> I'm a little skeptical about creating more memory tunables.  DBAs who
> are used to previous versions of PG will find that their vacuum is now
> really slow, because they adjusted maintenance_work_mem but not this

Also, generally people who are using autovacuum don't do much manual
vacuuming, and when they do, it's easy enough to do a SET before you
issue the VACUUM statement.

So, -1 for yet another GUC.

> new parameter.  If we could divide up the vacuum memory intelligently
> between the workers in some way, that would be a win.  But just
> creating a different variable that controls the same thing in
> different units doesn't seem to add much.

Actually, that's not unreasonable.  The difficulty with allocating
work_mem out of a pool involves concurrency, but use of maint_work_mem
is very low-concurrency; it wouldn't be that challenging to have the
autovac workers pull from a pool of preset size instead of each being
allocated the full maint_work_mem.  And that would help with over/under
allocation of memory.

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com