Re: Auto-tuning work_mem and maintenance_work_mem

On Thu, Oct 10, 2013 at 10:20:02AM -0700, Josh Berkus wrote:
> On 10/09/2013 02:15 PM, Bruce Momjian wrote:
> > and for shared_buffers of 2GB:
> > 
> >     test=> show shared_buffers;
> >      shared_buffers
> >     ----------------
> >      2GB
> >     (1 row)
> >     
> >     test=> SHOW work_mem;
> >      work_mem
> >     ----------
> >      6010kB
> >     (1 row)
> 
> Huh?  Only 6MB work_mem for 8GB RAM?  How'd you get that?

> That's way low, and frankly it's not worth bothering with this if all
> we're going to get is an incremental increase.  In that case, let's just
> set the default to 4MB like Robert suggested.

Uh, well, 100 backends at 6MB gives us 600MB, and if each backend uses
3x work_mem, that gives us 1.8GB for total work_mem.  This was based on
Andrew's concerns about possible over-commit of work_mem.  I can of
course adjust that.

Consider 8GB of shared memory is 21MB.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + Everyone has their own god. +