On Mon, Mar 13, 2017 at 4:59 AM, Amit Khandekar <amitdkhan...@gmail.com> wrote: > I agree that we should preferably have the non-partial plans started > first. But I am not sure if it is really worth ordering the partial > plans by cost. The reason we ended up not keeping track of the > per-subplan parallel_worker, is because it would not matter much , > and we would just equally distribute the workers among all regardless > of how big the subplans are. Even if smaller plans get more worker, > they will finish faster, and workers would be available to larger > subplans sooner.
Imagine that the plan costs are 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, and 10 and you have 2 workers. If you move that 10 to the front, this will finish in 10 time units. If you leave it at the end, it will take 15 time units. -- 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