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: Alexander Pyhalov <a.pyhalov@postgrespro.ru>, "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-06-02T16:09:03Z
Lists: pgsql-hackers 
On Thu, Jun 2, 2022 at 5:08 AM Etsuro Fujita <etsuro.fujita@gmail.com>
wrote:

> On Wed, Apr 6, 2022 at 3:58 PM Etsuro Fujita <etsuro.fujita@gmail.com>
> wrote:
> > I have committed the patch after modifying it as such.
>
> The patch calls trivial_subqueryscan() during create_append_plan() to
> determine the triviality of a SubqueryScan that is a child of an
> Append node.  Unlike when calling it from
> set_subqueryscan_references(), this is done before some
> post-processing such as set_plan_references() on the subquery.  The
> reason why this is safe wouldn't be that obvious, so I added to
> trivial_subqueryscan() comments explaining this.  Attached is a patch
> for that.
>
> Best regards,
> Etsuro Fujita
>
Hi,
Suggestion on formatting the comment:

+ * node (or that for any plan node in the subplan tree), 2)
+ * set_plan_references() modifies the tlist for every plan node in the

It would be more readable if `2)` is put at the beginning of the second
line above.

+ * preserves the length and order of the tlist, and 3)
set_plan_references()
+ * might delete the topmost plan node like an Append or MergeAppend from
the

Similarly you can move `3) set_plan_references()` to the beginning of the
next line.

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.