On Thu, Aug 12, 2010 at 12:37 PM, Scott Marlowe <scott.marl...@gmail.com>wrote:
> On Wed, Aug 11, 2010 at 11:41 PM, Greg Smith <g...@2ndquadrant.com> wrote: > > Sandeep Srinivasa wrote: > >> > >> Maybe a tabular form would be nice - "work_mem" under... > > > > The problem with work_mem in particular is that the useful range depends > > quite a bit on how complicated you expect the average query running to > be. > > And it's very dependent on max connections. A machine with 512GB that > runs batch processes for one or two import processes and then has > another two or three used to query it can run much higher work_mem > than a machine with 32G set to handle hundreds of concurrent accesses. > Don't forget that when you set work_mem to high it has a very sharp > dropoff in performance as swapping starts to occur. If work_mem is a > little low, queries run 2 or 3 times slower. If it's too high the > machine can grind to a halt. > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Right there - could this information not have been captured in the tabular form I was talking about ? Again, I'm not sure how to present the data, but it sure would be of *some* help to the next poor soul who comes along with same question. This here is golden knowledge - yes you might not be able to add all the qualifiers to just saying ">8GB use X work_mem", but it really, really is much better than nothing that we have now. -Sandeep
