> 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.
