Horton

Re: Proposal : Parallel Merge Join

Peter Geoghegan <pg@heroku.com>

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From: Peter Geoghegan <pg@heroku.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-12-11T02:44:02Z
Lists: pgsql-hackers 
On Sat, Dec 10, 2016 at 4:59 AM, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> 3. 20_patch.out  : Explain analyze output with patch (median of 3 runs)

I noticed that the partially parallelized Merge Join EXPLAIN ANALYZE
that you attach has a big misestimation:

->  Merge Join  (cost=3405052.45..3676948.66 rows=320 width=32)
(actual time=21165.849..37814.551 rows=1357812 loops=4)

Is this the best test case to show off the patch? This node is the
immediate outer child of a Nested Loop Semi Join, and so I'm concerned
that we measuring the wrong thing.

-- 
Peter Geoghegan

Commits

  1. Consider parallel merge joins.

  2. Preparatory refactoring for parallel merge join support.

  3. Fix parallel hash join path search.