Horton

Re: Default setting for enable_hashagg_disk

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>, Tom Lane <tgl@sss.pgh.pa.us>, Jeff Davis <pgsql@j-davis.com>, 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: 2020-07-13T19:57:27Z
Lists: pgsql-hackers, pgsql-docs 
On Mon, Jul 13, 2020 at 11:50 AM Peter Geoghegan <pg@bowt.ie> wrote:

>
> Primarily in favor of escape hatch:
>
> Jeff,
> DavidR,
> Pavel,
> Andres,
> Robert ??,
> Amit ??
>
>
To be clear, by "escape hatch" you mean "add a GUC that instructs the
PostgreSQL executor to ignore hash_mem when deciding whether to spill the
contents of the hash table to disk - IOW to never spill the contents of a
hash table to disk"?  If so that seems separate from whether to add a
hash_mem GUC to provide finer grained control - people may well want both.

Primarily in favor of hash_mem/hash_mem_multiplier:
>
> PeterG,
> Tom,
> Alvaro,
> Tomas,
> Justin,
> DavidG,
> Jonathan Katz
>
>
I would prefer DavidJ as an abbreviation - my middle initial can be dropped
when referring to me.

David J.

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.