On Fri, Mar 13, 2020 at 8:34 AM Andrew Gierth <and...@tao11.riddles.org.uk> wrote:
> >>>>> "Justin" == Justin Pryzby <pry...@telsasoft.com> writes: > > > On Thu, Mar 12, 2020 at 12:16:26PM -0700, Andres Freund wrote: > >> Indeed, that's incorrect. Causes the number of buckets for the > >> hashtable to be set higher - the size is just used for that. I'm a > >> bit wary of changing this in the stable branches - could cause > >> performance changes? > > I think (offhand, not tested) that the number of buckets would only be > affected if the (planner-supplied) numGroups value would cause work_mem > to be exceeded; the planner doesn't plan a hashagg at all in that case > unless forced to (grouping by a hashable but not sortable column). Note > that for various reasons the planner tends to over-estimate the memory > requirement anyway. > > That makes sense, thanks
