On Wed, Oct 9, 2013 at 03:04:24PM -0700, Peter Geoghegan wrote: > On Wed, Oct 9, 2013 at 2:15 PM, Bruce Momjian <br...@momjian.us> wrote: > > I did like Josh's idea about using autovacuum_max_workers for > > maintenance_work_mem, though I used the shared_buffers/4 calculation. > > I don't like that idea myself, because I wouldn't like to link > maintenance_work_mem to autovacuum_max_workers. > > As you yourself said, maintenance_work_mem exists because maintenance > operations are generally much less common than operations that service > queries. > > Couldn't you make the case that autovacuum also services queries? > Certainly, autovacuum can be expected to use multiple large > allocations of memory, once per worker. From the DBA's perspective, > this could be happening at any time, to any extent, much like with > work_mem allocations (though we at least bound these special > maintenance_work_mem allocations to at most autovacuum_max_workers). > So I really think the case is strong for a vacuum_work_mem (with a > default of -1 that means 'use maintenace_work_mem').
Splitting out vacuum_work_mem from maintenance_work_mem is a separate issue. I assume they were combined because the memory used for vacuum index scans is similar to creating an index. I am not sure if having two settings makes something more likely to be set --- I would think the opposite. > > Here are the defaults for two configurations; first, for the 128MB > > default shared_buffers: > > I am certainly supportive of the idea of improving our defaults here. > The bar is so incredibly low that anything is likely to be a big > improvement. What you've suggested here looks not unreasonable to me. > Have you thought about clamping the value too? I'm thinking of very > small shared_buffers sizings. After all, 128MB isn't the default in > the same way 1MB is presently the default work_mem setting. > > It is certainly true that shared_buffers size is a poor proxy for an > appropriate work_mem size, but does that really matter? Right, the bar is low, so almost anything is an improvement. I figure I will just keep tweeking the algorithm until no one complains. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
