Horton

Re: Default setting for enable_hashagg_disk

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: Bruce Momjian <bruce@momjian.us>, Jeff Davis <pgsql@j-davis.com>, 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: 2020-06-25T22:58:53Z
Lists: pgsql-hackers, pgsql-docs 
On 2020-Jun-25, Andres Freund wrote:

> >My point here is that maybe we don't need to offer a GUC to explicitly
> >turn spilling off; it seems sufficient to let users change work_mem so
> >that spilling will naturally not occur.  Why do we need more?
> 
> That's not really a useful escape hatch, because I'll often lead to
> other nodes using more memory.

Ah -- other nodes in the same query -- you're right, that's not good.

-- 
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.