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

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