Horton

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

Zhihong Yu <zyu@yugabyte.com>

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From: Zhihong Yu <zyu@yugabyte.com>
To: Etsuro Fujita <etsuro.fujita@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Alexander Pyhalov <a.pyhalov@postgrespro.ru>, "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2022-04-19T17:08:41Z
Lists: pgsql-hackers 
On Tue, Apr 19, 2022 at 2:01 AM Etsuro Fujita <etsuro.fujita@gmail.com>
wrote:

> Hi,
>
> On Sun, Apr 17, 2022 at 7:30 PM Zhihong Yu <zyu@yugabyte.com> wrote:
> > On Sun, Apr 17, 2022 at 1:48 AM Etsuro Fujita <etsuro.fujita@gmail.com>
> wrote:
> >> I think we might support more cases in the switch statement in the
> >> future.  My concern about your proposal is that it might make it hard
> >> to add new cases to the statement.  I agree that what I proposed has a
> >> bit of redundant code, but writing code inside each case independently
> >> would make it easy to add them, making code consistent across branches
> >> and thus making back-patching easy.
>
> > When a new case arises where the plan is not a Result node, this func
> can be rewritten.
> > If there is only one such new case, the check at the beginning of the
> func can be tuned to exclude that case.
>
> Sorry, I don't agree with you.
>
> > I still think the check should be lifted to the beginning of the func
> (given the current cases).
>
> The given path isn't limited to SubqueryScanPath, ForeignPath and
> ProjectionPath, so another concern is extra cycles needed when the
> path is other path type that is projection-capable (e.g., Path for
> sequential scan, IndexPath, NestPath, ...).  Assume that the given
> path is a Path (that doesn't contain pseudoconstant quals).  In that
> case the given SeqScan plan node wouldn't contain a gating Result
> node, so if we put the if test at the top of the function, we need to
> execute not only the test but the switch statement for the given
> path/plan nodes.  But if we put the if test inside each case block, we
> only need to execute the switch statement, without executing the test.
> In the latter case I think we can save cycles for normal cases.
>
> In short: I don't think it's a great idea to put the if test at the
> top of the function.
>
> Best regards,
> Etsuro Fujita
>
Hi,
It is okay to keep the formation in your patch.

Cheers

Commits

  1. Improve comments for trivial_subqueryscan().

  2. Disable asynchronous execution if using gating Result nodes.

  3. Allow asynchronous execution in more cases.

  4. Doc: Further update documentation for asynchronous execution.

  5. Fix rescanning of async-aware Append nodes.

  6. Doc: Update documentation for asynchronous execution.

  7. Fix EXPLAIN ANALYZE for async-capable nodes.

  8. Minor code cleanup in asynchronous execution support.

  9. Adjust input value to WaitEventSetWait() in ExecAppendAsyncEventWait().

  10. Add support for asynchronous execution.