On Tue, 31 Dec 2024 at 10:11, James Hunter <james.hunter...@gmail.com> wrote: > Does PostgreSQL currently rescan Hash Joins when they are "no longer > needed," to free work_mem early? If so, then I would try to reuse this > existing logic to decide which nodes need work_mem concurrently. > > If not, then all nodes that use work_mem actually use it > "concurrently," because we don't free that work_mem until we call > ExecutorEnd().
The problem with that statement is that Hash Join isn't the only node type that uses work_mem. Plenty of other node types do. Have a look at MultiExecBitmapOr(). You can see logic there that does tbm_free() after the tbm_union() call. Going by that, it seems there is at least one place where we might free some work_mem memory before allocating another lot. David
