Re: [PATCH] Incremental sort (was: PoC: Partial sort)

On Wed, Apr 8, 2020 at 9:43 AM Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>
> On Wed, Apr 08, 2020 at 12:51:05PM +0200, Tomas Vondra wrote:
> >On Tue, Apr 07, 2020 at 11:54:23PM -0400, Tom Lane wrote:
> >>hyrax is not too happy with this test:
> >>
> >>https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2020-04-07%2004%3A55%3A15
> >>
> >>It's not too clear to me why CLOBBER_CACHE_ALWAYS would be breaking
> >>EXPLAIN output, but it evidently is.
> >>
> >
> >Thanks, I'll investigate. It's not clear to me either what might be
> >causing this, but I guess something must have gone wrong in
> >estimation/planning.
> >
>
> OK, I know what's going on - it's a rather embarassing issue in the
> regression test. There's no analyze on the test tables, so it uses
> default estimates for number of groups etc. But with clobber cache the
> test runs long enough for autoanalyze to kick in and collect stats, so
> we generate better estimates which changes the plan.
>
> I'll get this fixed - explicit analyze and tweaking the data a bit
> should do the trick.

Looking at the tests that failed, I think we should consider just adding:
set enable_sort = off;
because several of those tests have very specific amounts of data to
ensure we test the transition points around the different modes in the
incremental sort node.

James