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: David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>
Cc: Peter Geoghegan <pg@bowt.ie>, Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@2ndquadrant.com>, 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: 2020-07-13T14:51:03Z
Lists: pgsql-hackers, pgsql-docs 
On Tue, 2020-07-14 at 02:25 +1200, David Rowley wrote:
> Updated summary:
> * For hash_mem = Tomas [7], Justin [16]
> * For hash_mem_multiplier with a default > 1.0 = DavidG [21]
> * For hash_mem_multiplier with default = 1.0 =  PeterG [15][0], Tom
> [20][24]

I am OK with these options, but I still prefer a simple escape hatch.

> * Maybe do nothing until we see how things go during beta = Bruce
> [3], Amit [10]
> * Just let users set work_mem = Stephen [21], Alvaro [4] (Alvaro
> changed his mind after Andres pointed out that changes other nodes in
> the plan too [25])

I am not on board with these options.

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.