On Thu, Jul 2, 2020 at 09:46:49PM -0500, Justin Pryzby wrote: > On Thu, Jul 02, 2020 at 07:05:48PM -0700, Peter Geoghegan wrote: > > anything else). I still think that the new GUC should work as a > > multiplier of work_mem, or something else along those lines, though > > for now it's just an independent work_mem used for hashing. I bring it > > up again because I'm concerned about users that upgrade to Postgres 13 > > incautiously, and find that hashing uses *less* memory than before. > > Many users probably get away with setting work_mem quite high across > > the board. At the very least, hash_mem should be ignored when it's set > > to below work_mem (which isn't what the patch does). > > I feel it should same as work_mem, as it's written, and not a multiplier. > > And actually I don't think a lower value should be ignored: "mechanism not > policy". Do we refuse atypical values of maintenance_work_mem < work_mem ? > > I assumed that hash_mem would default to -1, which would mean "fall back to > work_mem". We'd then advise users to increase it if they have an issue in v13 > with performance of hashes spilled to disk. (And maybe in other cases, too.)
Uh, with this patch, don't we really have sort_mem and hash_mem, but hash_mem default to sort_mem, or something like that. If hash_mem is a multiplier, it would make more sense to keep the work_mem name. -- Bruce Momjian <br...@momjian.us> https://momjian.us EnterpriseDB https://enterprisedb.com The usefulness of a cup is in its emptiness, Bruce Lee
