Re: Performance degradation in Bitmapscan (commit 75ae538bc3168bf44475240d4e0487ee2f3bb376)

On 2017-01-06 11:01:32 -0500, Robert Haas wrote:
> On Fri, Jan 6, 2017 at 10:43 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On 2016-12-16 09:34:31 -0800, Andres Freund wrote:
> >> > To fix his issue, we need something like your 0001. Are you going to
> >> > polish that up soon here?
> >>
> >> Yes.
> >
> > I've two versions of a fix for this. One of them basically increases the
> > "spread" of buckets when the density goes up too much. It does so by
> > basically shifting the bucket number to the left (e.g. only every second
> > bucket can be the "primary" bucket for a hash value). The other
> > basically just replaces the magic constants in my previous POC patch
> > with slightly better documented constants. For me the latter works just
> > as well as the former, even though aesthetically/theoretically the
> > former sounds better. I'm inclined to commit the latter, at least for
> > now.
>
> Did you intend to attach the patches?

No, I hadn't. You're interested in the "spreading" version?

Andres