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: Zhihong Yu <zyu@yugabyte.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: 2022-04-04T04:06:40Z
Lists: pgsql-hackers 
Hi Zhihong,

On Sun, Apr 3, 2022 at 11:38 PM Zhihong Yu <zyu@yugabyte.com> wrote:
> +   WRITE_ENUM_FIELD(status, SubqueryScanStatus);
>
> Looks like the new field can be named subquerystatus - this way its purpose is clearer.

I agree that “status” is too general.  “subquerystatus” might be good,
but I’d like to propose “scanstatus” instead, because I think this
would be consistent with the naming of the RowMarkType-enum member
“markType” in PlanRowMark defined in the same file.

> + * mark_async_capable_plan
> + *     Check whether a given Path node is async-capable, and if so, mark the
> + *     Plan node created from it as such.
>
> Please add comment explaining what the return value means.

Ok, how about something like this?

“Check whether a given Path node is async-capable, and if so, mark the
Plan node created from it as such and return true; otherwise, return
false.”

> +           if (!IsA(plan, Result) &&
> +               mark_async_capable_plan(plan,
> +                                       ((ProjectionPath *) path)->subpath))
> +               return true;
>
> by returning true, `plan->async_capable = true;` is skipped.
> Is that intentional ?

That is intentional; we don’t need to set the async_capable flag
because in that case the flag would already have been set by the above
mark_async_capable_plan().  Note that we pass “plan” to that function.

Thanks for reviewing!

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.