Horton

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

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Rushabh Lathia <rushabh.lathia@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Pg Hackers <pgsql-hackers@postgresql.org>, Corey Huinker <corey.huinker@gmail.com>
Date: 2018-01-18T18:30:46Z
Lists: pgsql-hackers 
On Thu, Jan 18, 2018 at 6:14 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> I see your point.  OTOH, I think we should have something for testing
> purpose as that helps in catching the bugs and makes it easy to write
> tests that cover worker part of the code.

This is about the question of whether or not we want to allow
parallel_leader_participation to prevent or allow a parallel CREATE
INDEX that has 1 parallel worker that does all the sorting, with the
leader simply consuming its output without doing any merging (a
"degenerate paralllel CREATE INDEX"). It is perhaps only secondarily
about the question of ripping out parallel_leader_participation
entirely.

> Can you please elaborate what part of optimizer are you talking about
> where without leader participation partial path will always lose to a
> serial sequential scan path?

See my remarks to Robert just now.

-- 
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