Horton

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

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: James Coleman <jtc331@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Michael Paquier <michael@paquier.xyz>, Rafia Sabih <rafia.pghackers@gmail.com>, Peter Geoghegan <pg@bowt.ie>, Simon Riggs <simon@2ndquadrant.com>, Shaun Thomas <shaun.thomas@2ndquadrant.com>, Dmitry Dolgov <9erthalion6@gmail.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>, Andreas Karlsson <andreas@proxel.se>
Date: 2020-04-08T13:43:35Z
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

Commits

  1. Further adjustments to Hashagg EXPLAIN ANALYZE output

  2. Rework EXPLAIN format for incremental sort

  3. Fix typos and improve incremental sort comments

  4. Stabilize incremental_sort tests

  5. Minor improvements in Incremental Sort explain

  6. Consider Incremental Sort paths at additional places

  7. Fix representation of SORT_TYPE_STILL_IN_PROGRESS.

  8. Fix failures in incremental_sort due to number of workers

  9. Fix show_incremental_sort_info with force_parallel_mode

  10. Implement Incremental Sort

  11. Fix handling of "Subplans Removed" field in EXPLAIN output.

  12. Fix EXPLAIN (SETTINGS) to follow policy about when to print empty fields.

  13. Ensure plpgsql result tuples have the right composite type marking.

  14. Propagate sort instrumentation from workers back to leader.

  15. Make new regression test case parallel-safe, and improve its output.

  16. Push limit through subqueries to underlying sort, where possible.

  17. Fix inappropriate printing of never-measured times in EXPLAIN.

  18. Fix some infelicities in EXPLAIN output for parallel query plans.