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: David Rowley <dgrowleyml@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>, "David G. Johnston" <david.g.johnston@gmail.com>, Stephen Frost <sfrost@snowman.net>, 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: 2020-07-11T14:27:02Z
Lists: pgsql-hackers, pgsql-docs 
David Rowley <dgrowleyml@gmail.com> writes:
> hmm yeah. It's unfortunate, but I'm not sure how I'd have implemented
> it differently.  The problem is made worse by the fact that we'll only
> release the memory for the hash table during ExecEndHashJoin(). If the
> planner had some ability to provide the executor with knowledge that
> the node would never be rescanned, then the executor could release the
> memory for the hash table after the join is complete.

EXEC_FLAG_REWIND seems to fit the bill already?

			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.