Re: Auto-tuning work_mem and maintenance_work_mem

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.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +

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