Horton

Re: Asynchronous Append on postgres_fdw nodes.

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: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-05-06T06:45:06Z
Lists: pgsql-hackers

Attachments

On Tue, Apr 27, 2021 at 9:31 PM Etsuro Fujita <etsuro.fujita@gmail.com> wrote:
> On Mon, Apr 26, 2021 at 7:35 PM Andrey V. Lepikhov
> <a.lepikhov@postgrespro.ru> wrote:
> > Small mistake i found. If no tuple was received from a foreign
> > partition, explain shows that we never executed node.

> > The patch in the attachment fixes this.
>
> Will look into this.

The patch fixes the issue, but I don’t think it’s the right way to go,
because it requires an extra ExecProcNode() call, which wouldn’t be
efficient.  Also, the patch wouldn’t address another issue I noticed
in EXPLAIN ANALYZE for async-capable nodes that the command wouldn’t
measure the time spent in such nodes accurately.  For the case of
async-capable node using postgres_fdw, it only measures the time spent
in ExecProcNode() in ExecAsyncRequest()/ExecAsyncNotify(), missing the
time spent in other things such as creating a cursor in
ExecAsyncRequest().  :-(.  To address both issues, I’d like to propose
the attached, in which I added instrumentation support to
ExecAsyncRequest()/ExecAsyncConfigureWait()/ExecAsyncNotify().  I
think this would not only address the reported issue more efficiently,
but allow to collect timing for async-capable nodes more accurately.

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.