Re: Parallel Append implementation

On Mon, Mar 13, 2017 at 7:46 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Mon, Mar 13, 2017 at 4:59 AM, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)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.

Oh, never mind. You were only asking whether we should sort partial
plans. That's a lot less important, and maybe not important at all.
The only consideration there is whether we might try to avoid having
the leader start in on a plan with a large startup cost.

--
Robert Haas
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