Re: [PATCHES] Better default_statistics_target

On Jan 31, 2008 12:08 AM, Gregory Stark <stark(at)enterprisedb(dot)com> wrote:
> "Decibel!" <decibel(at)decibel(dot)org> writes:
>
> > I think that before doing any of that you'd be much better off
> > investigating how much performance penalty there is for maxing out
> > default_statistict_target. If, as I suspect, it's essentially 0 on
> > modern hardware, then I don't think it's worth any more effort.
>
> That's not my experience. Even just raising it to 100 multiplies the number of
> rows ANALYZE has to read by 10. And the arrays for every column become ten
> times larger. Eventually they start being toasted...

+1. From the tests I did on our new server, I set the
default_statistict_target to 30. Those tests were mainly based on the
ANALYZE time though, not the planner overhead introduced by larger
statistics - with higher values, I considered the ANALYZE time too
high for the benefits. I set it higher on a per column basis only if I
see it can lead to better stats but from all the tests I did so far,
it was sufficient for our data set.

--
Guillaume