Horton

Re: Default setting for enable_hashagg_disk

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Jeff Davis <pgsql@j-davis.com>, David Rowley <dgrowleyml@gmail.com>, Stephen Frost <sfrost@snowman.net>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2020-07-27T18:24:36Z
Lists: pgsql-hackers, pgsql-docs 
On 2020-Jul-27, Peter Geoghegan wrote:

> On Mon, Jul 27, 2020 at 10:30 AM Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:
> > On 2020-Jul-23, Peter Geoghegan wrote:
> > I notice you put the prototype for get_hash_mem in nodeHash.h.  This
> > would be fine if not for the fact that optimizer needs to call the
> > function too, which means now optimizer have to include executor headers
> > -- not a great thing.  I'd move the prototype elsewhere to avoid this,
> > and I think miscadmin.h is a decent place for the prototype, next to
> > work_mem and m_w_m.
> 
> The location of get_hash_mem() is awkward,

Yes.

> but there is no obvious alternative.

Agreed.

> Are you proposing that I just put the prototype in miscadmin.h, while
> leaving the implementation where it is (in nodeHash.c)?

Yes, that's in the part of my reply you didn't quote:

: It remains strange to have the function in executor
: implementation, but I don't offhand see a better place, so maybe it's
: okay where it is.

> [...] moving the implementation of get_hash_mem() to either of those
> two files seems worse to me.

Sure.

-- 
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.