On Wed, Jun 24, 2020 at 3:14 PM Andres Freund <and...@anarazel.de> wrote: > FWIW, my gut feeling is that we'll end up have to separate the > "execution time" spilling from using plain work mem, because it'll > trigger spilling too often. E.g. if the plan isn't expected to spill, > only spill at 10 x work_mem or something like that. Or we'll need > better management of temp file data when there's plenty memory > available.
So, I don't think we can wire in a constant like 10x. That's really unprincipled and I think it's a bad idea. What we could do, though, is replace the existing Boolean-valued GUC with a new GUC that controls the size at which the aggregate spills. The default could be -1, meaning work_mem, but a user could configure a larger value if desired (presumably, we would just treat a value smaller than work_mem as work_mem, and document the same). I think that's actually pretty appealing. Separating the memory we plan to use from the memory we're willing to use before spilling seems like a good idea in general, and I think we should probably also do it in other places - like sorts. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
