Re: Default setting for enable_hashagg_disk (hash_mem)

On Tue, Jul 7, 2020 at 10:12 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> I think it makes no too much sense to plan invent something like
> hash_mem for v13, it's clearly too much work. That's a seperate
> discussion from having something like it for v14.

Can you explain why you believe that to be the case? It seems quite
possible that there is some subtlety that I missed in grouping sets or
something like that. I would like to know the specifics, if there are
any specifics.

> My conclusion about this topic is that I think we'll be doing our users
> a disservice by not providing an escape hatch, but that I also don't
> have the energy / time to fight for it further. This is a long thread
> already, and I sense little movement towards a conclusion.

An escape hatch seems necessary. I accept that a hard disabling of
spilling at execution time meets that standard, and that may be enough
for Postgres 13. But I am concerned that an uncomfortably large
proportion of our users will end up needing this. (Perhaps I should
say a large proportion of the subset of users that might be affected
either way. You get the idea.)

I have to wonder if this escape hatch is an escape hatch for our
users, or an escape hatch for us. There is a difference.

--
Peter Geoghegan