Re: Defer selection of asynchronous subplans until the executor initialization stage

On Mon, May 10, 2021 at 8:45 PM Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>
wrote:

> On 7/5/21 21:05, Etsuro Fujita wrote:
> > I think it would be better to start a new thread for this, and add the
> > patch to the next CF so that it doesn’t get lost.
>
> Current implementation of async append choose asynchronous subplans at
> the phase of an append plan creation. This is safe approach, but we
> loose some optimizations, such of flattening trivial subqueries and
> can't execute some simple queries asynchronously. For example:
>
> EXPLAIN (ANALYZE, TIMING OFF, SUMMARY OFF, COSTS OFF)
> (SELECT * FROM f1 WHERE a < 10) UNION ALL
> (SELECT * FROM f2 WHERE a < 10);
>
> But, as I could understand, we can choose these subplans later, at the
> init append phase when all optimizations already passed.
> In attachment - implementation of the proposed approach.
>
> Initial script for the example see in the parent thread [1].
>
>
> [1]
>
> https://www.postgresql.org/message-id/a38bb206-8340-9528-5ef6-37de2d5cb1a3%40postgrespro.ru
>
>
> --
> regards,
> Andrey Lepikhov
> Postgres Professional
>
Hi,

+ /* Check to see if subplan can be executed asynchronously */
+ if (subplan->async_capable)
+ {
+ subplan->async_capable = false;

It seems the if statement is not needed: you can directly assign false
to subplan->async_capable.

Cheers