Horton

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

Etsuro Fujita <etsuro.fujita@gmail.com>

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From: Etsuro Fujita <etsuro.fujita@gmail.com>
To: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
Cc: Zhihong Yu <zyu@yugabyte.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-08-30T09:52:12Z
Lists: pgsql-hackers

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On Mon, Aug 30, 2021 at 5:36 PM Andrey V. Lepikhov
<a.lepikhov@postgrespro.ru> wrote:
> On 8/23/21 2:18 PM, Etsuro Fujita wrote:
> > To just execute what was planned at execution time, I think we should
> > return to the patch in [1].  The patch was created for Horiguchi-san’s
> > async-execution patch, so I modified it to work with HEAD, and added a
> > simplified version of your test cases.  Please find attached a patch.

> > [1] https://www.postgresql.org/message-id/7fe10f95-ac6c-c81d-a9d3-227493eb9055@postgrespro.ru

> I agree, this way is more safe. I tried to search for another approach,
> because here isn't general solution: for each plan node we should
> implement support of asynchronous behaviour.

I think so too.

> But for practical use, for small set of nodes, it will work good. I
> haven't any objections for this patch.

OK

To allow async execution in a bit more cases, I modified the patch a
bit further: a ProjectionPath put directly above an async-capable
ForeignPath would also be considered async-capable as ForeignScan can
project and no separate Result is needed in that case, so I modified
mark_async_capable_plan() as such, and added test cases to the
postgres_fdw regression test.  Attached is an updated version of the
patch.

Thanks for the review!

Best regards,
Etsuro Fujita

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.