On Wed, Oct 9, 2013 at 04:32:44PM +0200, Andres Freund wrote: > On 2013-10-09 10:30:46 -0400, Bruce Momjian wrote: > > Josh Berkus suggested here that work_mem and maintenance_work_mem could > > be auto-tuned like effective_cache_size: > > > > http://www.postgresql.org/message-id/50ECCF93.3060101@agliodbs.com > > > > The attached patch implements this, closely matching the default values > > for the default shared_buffers value: > > There imo is no correlation between correct values for shared_buffers > and work_mem at all. They really are much more workload dependant than > anything.
Well, that is true, but the more shared_buffers you allocate, the more work_mem you _probably_ want to use. This is only a change of the default.
Effectively, if every session uses one full work_mem, you end up with total work_mem usage equal to shared_buffers.
We can try a different algorithm to scale up work_mem, but it seems wise to auto-scale it up to some extent based on shared_buffers.
In my experience a optimal value of work_mem depends on data and load, so I prefer a work_mem as independent parameter.
maintenance_work_mem can depend on work_mem ~ work_mem * 1 * max_connection / 4
