Horton

Re: Default setting for enable_hashagg_disk

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Peter Geoghegan <pg@bowt.ie>, Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2020-07-28T00:10:41Z
Lists: pgsql-hackers, pgsql-docs 
On Mon, 2020-07-27 at 11:30 -0700, Peter Geoghegan wrote:
> The v4-0001-Remove-hashagg_avoid_disk_plan-GUC.patch changes are
> surprisingly complicated. It would be nice if you could take a look
> at
> that aspect (or confirm that it's included in your review).

I noticed that one of the conditionals, "cheapest_total_path != NULL",
was already redundant with the outer conditional before your patch. I
guess that was just a mistake which your patch corrects along the way?

Anyway, the patch looks good to me. We can have a separate discussion
about pessimizing the costing, if necessary.

Regards,
	Jeff Davis

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.