Re: MySQL versus Postgres

On Thu, Aug 12, 2010 at 12:37 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>wrote:

> On Wed, Aug 11, 2010 at 11:41 PM, Greg Smith <greg(at)2ndquadrant(dot)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