Horton

Re: Default setting for enable_hashagg_disk (hash_mem)

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Jeff Davis <pgsql@j-davis.com>, Bruce Momjian <bruce@momjian.us>, Peter Geoghegan <pg@bowt.ie>, Justin Pryzby <pryzby@telsasoft.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, David Rowley <dgrowleyml@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-07-07T20:18:21Z
Lists: pgsql-hackers, pgsql-docs 
On 2020-Jul-07, Amit Kapila wrote:

> I don't think this is true.  We seem to have introduced three new guc
> variables in a 9.3.3 minor release.

Yeah, backporting GUCs is not a big deal.  Sure, the GUC won't appear in
postgresql.conf files generated by initdb prior to the release that
introduces it.  But users that need it can just edit their .confs and
add the appropriate line, or just do ALTER SYSTEM after the minor
upgrade.  For people that don't need it, it would have a reasonable
default (probably work_mem, so that behavior doesn't change on the minor
upgrade).

-- 
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.