Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: James Coleman <jtc331@gmail.com>
Cc: Tomas Vondra <tomas.vondra@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>, Alvaro Herrera <alvherre@2ndquadrant.com>
Date: 2020-03-13T17:36:44Z
Lists: pgsql-hackers 
James Coleman <jtc331@gmail.com> writes:
> On Tue, Mar 10, 2020 at 10:44 PM Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
>> 1) I see a bunch of failures in the regression test, due to minor
>> differences in the explain output. All the differences are about minor
>> changes in memory usage, like this:
>> 
>> -               "Sort Space Used": 30,                             +
>> +               "Sort Space Used": 29,                             +
>> 
>> I'm not sure if it happens on my machine only, but maybe the test is not
>> entirely stable.

> make check passes on multiple machines for me; what arch/distro are you using?

I think there's exactly zero chance of such output being stable across
different platforms, particularly 32-vs-64-bit.  You'll need to either
drop that test or find some way to mask the variability.

> Is there a better way to test these? I would prefer these code paths
> have test coverage, but the standard SQL tests don't leave a good way
> to handle stuff like this.

In some places we use plpgsql code to filter the EXPLAIN output.

			regards, tom lane

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.