| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Justin Pryzby <pryzby(at)telsasoft(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, David Rowley <dgrowleyml(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Default setting for enable_hashagg_disk |
| Date: | 2020-06-24 18:40:50 |
| Message-ID: | 2217145.1593024050@sss.pgh.pa.us |
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| Lists: | pgsql-docs pgsql-hackers |
Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> On Wed, Jun 24, 2020 at 01:29:56PM -0400, Tom Lane wrote:
>> If we feel we need something to let people have the v12 behavior
>> back, let's have
>> (1) enable_hashagg on/off --- controls planner, same as it ever was
>> (2) enable_hashagg_spill on/off --- controls executor by disabling spill
> What if a user specifies
> enable_hashagg = on
> enable_hashagg_spill = off
It would probably be reasonable for the planner to behave as it did
pre-v13, that is not choose hashagg if it estimates that work_mem
would be exceeded. (So, okay, that means enable_hashagg_spill
affects both planner and executor ... but ISTM it's just one
behavior not two.)
regards, tom lane
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