Horton

Re: Default setting for enable_hashagg_disk

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Jeff Davis <pgsql@j-davis.com>, Stephen Frost <sfrost@snowman.net>, Alvaro Herrera <alvherre@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, Bruce Momjian <bruce@momjian.us>, Robert Haas <robertmhaas@gmail.com>, David Rowley <dgrowleyml@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: 2020-07-10T21:30:41Z
Lists: pgsql-hackers, pgsql-docs 
Peter Geoghegan <pg@bowt.ie> writes:
> It now seems likely that the hash_mem/hash_mem_multiplier proposal has
> the support it needs to get into Postgres 13. Assuming that the
> proposal doesn't lose momentum, then it's about time to return to the
> original question you posed at the start of the thread:

> What should we do with the hashagg_avoid_disk_plan GUC (formerly known
> as the enable_hashagg_disk GUC), if anything?

> I myself think that there is a case to be made for removing it
> entirely.

+0.5 or so for removing it.  It seems too confusing and dubiously
useful.

			regards, tom lane

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.