Horton

Re: [HACKERS] [PATCH] Incremental sort

Teodor Sigaev <teodor@sigaev.ru>

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From: Teodor Sigaev <teodor@sigaev.ru>
To: Tom Lane <tgl@sss.pgh.pa.us>, Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Darafei Komяpa Praliaskouski <me@komzpa.net>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Antonin Houska <ah@cybertec.at>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2018-04-07T16:18:00Z
Lists: pgsql-hackers 
> I dunno, how would you estimate whether this is actually a win or not?
> I don't think our model of sort costs is anywhere near refined enough
> or accurate enough to reliably predict whether this is better than
> just doing it in one step.  Even if the cost model is good, it's not
> going to be better than our statistics about the number/size of the
> groups in the first column(s), and that's a notoriously unreliable stat.
I think that improvement in cost calculation of sort should be a 
separate patch, not directly connected to this one. Postpone patches 
till other part will be ready to get max improvement for postponed ones 
doesn't seem to me very good, especially if it suggests some improvement 
right now.


-- 
Teodor Sigaev                      E-mail: teodor@sigaev.ru
                                       WWW: http://www.sigaev.ru/

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.