Horton

Re: [PATCH] Incremental sort

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Mithun Cy <mithun.cy@enterprisedb.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-04-27T14:06:52Z
Lists: pgsql-hackers 
On Wed, Apr 26, 2017 at 11:39 AM, Alexander Korotkov
<a.korotkov@postgrespro.ru> wrote:
> But I'd like to make incremental sort not slower than quicksort in case of
> presorted data.  New idea about it comes to my mind.  Since cause of
> incremental sort slowness in this case is too frequent reset of tuplesort,
> then what if we would artificially put data in larger groups.  Attached
> revision of patch implements this: it doesn't stop to accumulate tuples to
> tuplesort until we have MIN_GROUP_SIZE tuples.
>
> Now, incremental sort is not slower than quicksort.  And this seems to be
> cool.
> However, in the LIMIT case we will pay the price of fetching some extra
> tuples from outer node.  But, that doesn't seem to hurt us too much.
>
> Any thoughts?

Nice idea.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.