On Thu, Oct 5, 2017 at 6:29 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: > Okay, but can't we try to pick the cheapest partial path for master > backend and maybe master backend can try to work on a partial path > which is already picked up by some worker.
Well, the master backend is typically going to be the first process to arrive at the Parallel Append because it's already running, whereas the workers have to start. So in the case that really matters, no paths will have been picked yet. Later on, we could have the master try to choose a path on which some other worker is already working, but I really doubt that's optimal. Either the workers are generating a lot of tuples (in which case the leader probably won't do much work on any path because it will be busy reading tuples) or they are generating only a few tuples (in which case the leader is probably better off working on an a path not yet chosen, to reduce contention). -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers