Re: Default setting for enable_hashagg_disk

On Mon, Jul 13, 2020 at 12:57 PM David G. Johnston
<david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
> To be clear, by "escape hatch" you mean "add a GUC that instructs the PostgreSQL executor to ignore hash_mem when deciding whether to spill the contents of the hash table to disk - IOW to never spill the contents of a hash table to disk"?

Yes, that's what that means.

> If so that seems separate from whether to add a hash_mem GUC to provide finer grained control - people may well want both.

They might want the escape hatch too, as an additional measure, but my
assumption is that anybody in favor of the
hash_mem/hash_mem_multiplier proposal takes that position because they
think that it's the principled solution. That's the kind of subtlety
that is bound to get lost when summarizing general sentiment at a high
level. In any case no individual has seriously argued that there is a
simultaneous need for both -- at least not yet.

This thread is already enormous, and very hard to keep up with. I'm
trying to draw a line under the discussion. For my part, I have
compromised on the important question of the default value of
hash_mem_multiplier -- I am writing a new version of the patch that
makes the default 1.0 (i.e. no behavioral changes by default).

> I would prefer DavidJ as an abbreviation - my middle initial can be dropped when referring to me.

Sorry about that.

--
Peter Geoghegan