Joshua D. Drake wrote: > > > On Wed, 2008-05-28 at 16:59 -0700, Josh Berkus wrote: > > Folks, > > > shared_buffers: according to witnesses, Greg Smith presented at > > East that based on PostgreSQL's buffer algorithms, buffers above > > 2GB would not really receive significant use. However, Jignesh > > Shah has tested that on workloads with large numbers of > > connections, allocating up to 10GB improves performance. > > I have seen multiple production systems where upping the buffers up to > 6-8GB helps. What I don't know, and what I am guessing Greg is > referring to is if it helps as much as say upping to 2GB. E.g; the > scale of performance increase goes down while the actual performance > goes up (like adding more CPUs).
That could be it. I'm one of the people who recall *something* about it, but I don't remember any specifics :-) > > sort_mem: My tests with 8.2 and DBT3 seemed to show that, due to > > limitations of our tape sort algorithm, allocating over 2GB for a > > single sort had no benefit. However, Magnus and others have > > claimed otherwise. Has this improved in 8.3? > > I have never see work_mem (there is no sort_mem Josh) do any good > above 1GB. Of course, I would never willingly use that much work_mem > unless there was a really good reason that involved a guarantee of > not calling me at 3:00am. I have. Not as a system-wide setting, but for a single batch job doing *large* queries. Don't recall exactly, but it wasn't necessarily for sort - might have been for hash. I've seen it make a *big* difference. maintenance_work_mem, however, I didn't see much difference upping it past 1Gb or so. //Magnus -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
