Horton

Re: Default setting for enable_hashagg_disk

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Jeff Davis <pgsql@j-davis.com>, David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>, Peter Geoghegan <pg@bowt.ie>, Andres Freund <andres@anarazel.de>, Bruce Momjian <bruce@momjian.us>, Robert Haas <robertmhaas@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Melanie Plageman <melanieplageman@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2020-07-13T18:38:23Z
Lists: pgsql-hackers, pgsql-docs 
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> I'm in favor of hash_mem_multiplier.  I think a >1 default is more
> sensible than =1 in the long run, but if strategic vote is what we're
> doing, then I support the =1 option.

FWIW, I also think that we'll eventually end up with >1 default.
But the evidence to support that isn't really there yet, so
I'm good with 1.0 default to start with.

			regards, tom lane

Commits

  1. Add hash_mem_multiplier GUC.

  2. HashAgg: use better cardinality estimate for recursive spilling.

  3. Remove hashagg_avoid_disk_plan GUC.

  4. Doc fixup for hashagg_avoid_disk_plan GUC.

  5. Rework HashAgg GUCs.

  6. Disk-based Hash Aggregation.

  7. Implement partition-wise grouping/aggregation.

  8. Defer creation of partially-grouped relation until it's needed.