On Fri, Nov 17, 2017 at 3:23 PM, Robert Haas <robertmh...@gmail.com> wrote: > Hmm. I wonder if you are correct that hashing is the special case. > Hashing and sorting are of course the two main operations -- but > there's materialize and anything else that uses a CTE, and maybe other > stuff I'm not thinking about right now. You might be right that hash > is the one where it really matters, but it's probably worth a bit more > reflection on where it matters most and for what reasons.
I'd rather be approximately correct than precisely wrong. I think that the current work_mem model is precisely wrong. I'm conscious of the fact that we are loathe to create new GUCs (I sometimes think that we're a bit too averse to doing so), but maybe there is room for adding a second work_mem-alike GUC. For now, I admit that I am applying fuzzy criteria, and that I could easily have missed an important subtlety. Creating hash_mem instead of sort_mem is a direction that is entirely debatable, and should actually be debated. OTOH, it seems like a real problem that we don't allow hashing to take full advantage of available main memory, and *some* interim solution seems preferable to what we have now. -- Peter Geoghegan
