Horton

Re: Parallel tuplesort (for parallel B-Tree index creation)

Peter Geoghegan <pg@heroku.com>

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From: Peter Geoghegan <pg@heroku.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Robert Haas <robertmhaas@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>, Corey Huinker <corey.huinker@gmail.com>
Date: 2016-09-07T05:40:20Z
Lists: pgsql-hackers 
On Tue, Sep 6, 2016 at 10:36 PM, Peter Geoghegan <pg@heroku.com> wrote:
> Well, maybe, but the whole idea behind replacement_sort_tuples (by
> which I mean the continued occasional use of replacement selection by
> Postgres) was that we hope to avoid a merge step *entirely*. This new
> merge shift down heap patch could make the merge step so cheap as to
> be next to free anyway (in the even of presorted input)

I mean: Cheaper than just processing the tuples to return to caller
without comparisons/merging (within the TSS_SORTEDONTAPE path). I do
not mean free in an absolute sense, of course.

-- 
Peter Geoghegan

Commits

  1. Support parallel btree index builds.

  2. Report an ERROR if a parallel worker fails to start properly.

  3. Transfer state pertaining to pending REINDEX operations to workers.

  4. Add a barrier primitive for synchronizing backends.

  5. Allow DML commands that create tables to use parallel query.

  6. Refactor GetOldestXmin() to use flags

  7. Fix regression in parallel planning against inheritance tables.

  8. Don't create "holes" in BufFiles, in the new logtape code.

  9. Simplify the code for logical tape read buffers.

  10. Fix excessive memory consumption in the new sort pre-reading code.

  11. Implement binary heap replace-top operation in a smarter way.

  12. Cosmetic code cleanup in commands/extension.c.

  13. Speed up planner's scanning for parallel-query hazards.

  14. Read from the same worker repeatedly until it returns no tuple.

  15. Improve tuplesort.c to support variable merge order. The original coding