On Wed, Apr 08, 2020 at 09:54:42AM -0400, James Coleman wrote:
On Wed, Apr 8, 2020 at 9:43 AM Tomas Vondra
<tomas.von...@2ndquadrant.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.
Maybe, but I'd much rather tweak the data so that we test both the
costing and execution part.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
