Horton

Re: Default setting for enable_hashagg_disk

Stephen Frost <sfrost@snowman.net>

View thread View on postgr.es
From: Stephen Frost <sfrost@snowman.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Peter Geoghegan <pg@bowt.ie>, 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>, 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: 2020-07-10T21:52:02Z
Lists: pgsql-hackers, pgsql-docs 
Greetings,

* Tom Lane (tgl@sss.pgh.pa.us) wrote:
> 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.

I agree that it shouldn't exist.

Thanks,

Stephen

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.