Horton

Re: Default setting for enable_hashagg_disk

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>, Peter Geoghegan <pg@bowt.ie>, 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: 2020-07-13T16:47:36Z
Lists: pgsql-hackers, pgsql-docs 
On 2020-Jul-13, Jeff Davis wrote:

> 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.

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.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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.