On Wed, Mar 8, 2017 at 5:33 PM, Robert Haas <robertmh...@gmail.com> wrote: >> pg_restore will avoid parallelism (that will happen by setting >> "max_parallel_workers_maintenance = 0" when it runs), not because it >> cannot trust the cost model, but because it prefers to parallelize >> things its own way (with multiple restore jobs), and because execution >> speed may not be the top priority for pg_restore, unlike a live >> production system. > > This part I'm not sure about. I think people care quite a lot about > pg_restore speed, because they are often down when they're running it. > And they may have oodles mode CPUs that parallel restore can use > without help from parallel query. I would be inclined to leave > pg_restore alone and let the chips fall where they may.
I thought that we might want to err on the side of preserving the existing behavior, but arguably that's actually what I failed to do. That is, since we don't currently have a pg_restore flag that controls the maintenance_work_mem used by pg_restore, "let the chips fall where they may" is arguably the standard that I didn't uphold. It might still make sense to take a leaf out of the parallel query book on this question. That is, add an open item along the lines of "review behavior of pg_restore with parallel CREATE INDEX" that we plan to deal with close to the release of Postgres 10.0, when feedback from beta testing is in. There are a number of options, none of which are difficult to write code for. The hard part is determining what makes most sense for users on balance. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers