| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | James Coleman <jtc331(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Shaun Thomas <shaun(dot)thomas(at)2ndquadrant(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andreas Karlsson <andreas(at)proxel(dot)se> |
| Subject: | Re: [PATCH] Incremental sort (was: PoC: Partial sort) |
| Date: | 2020-04-08 13:43:35 |
| Message-ID: | 20200408134335.arf7tgzhmm3mpxbl@development |
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| Lists: | pgsql-hackers |
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.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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