Horton

Re: Default setting for enable_hashagg_disk

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Jeff Davis <pgsql@j-davis.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>, Andres Freund <andres@anarazel.de>, Bruce Momjian <bruce@momjian.us>, Justin Pryzby <pryzby@telsasoft.com>, Melanie Plageman <melanieplageman@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2020-07-27T15:38:21Z
Lists: pgsql-hackers, pgsql-docs 
On Sun, Jul 26, 2020 at 11:34 AM Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> That's 1.6GB, if I read it right. Which is more than 200MB ;-)

Sigh. That solves that "mystery": the behavior that my sorted vs
random example exhibited is a known limitation in hash aggs that spill
(and an acceptable one). The memory usage is reported on accurately by
EXPLAIN ANALYZE.

-- 
Peter Geoghegan

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.