On Mon, Feb 14, 2022 at 10:32:43PM -0800, Peter Geoghegan wrote: > On Wed, Jan 19, 2022 at 11:32 AM John Naylor > <john.nay...@enterprisedb.com> wrote: > > I don't have anything really profound to say here, but in the last > > year I did on a couple occasions recommend clients to raise > > hash_mem_multiplier to 2.0 to fix performance problems. > > I would like to push ahead with an increase in the default for > Postgres 15, to 2.0. > > Any objections to that plan?
The only reason not to is that a single-node hash-aggregate plan will now use 2x work_mem. Which won't make sense to someone who doesn't deal with complicated plans (and who doesn't know that work_mem is per-node and can be used multiplicitively). I don't see how one could address that other than to change hash_mem_multiplier to nonhash_mem_divider. It'll be in the release notes, so should be fine. -- Justin
