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: 2022-04-10T13:46:25Z
Lists: pgsql-hackers 
On Sun, Apr 10, 2022 at 3:42 AM Etsuro Fujita <etsuro.fujita@gmail.com>
wrote:

> On Sat, Apr 9, 2022 at 1:58 AM Etsuro Fujita <etsuro.fujita@gmail.com>
> wrote:
> > On Fri, Apr 8, 2022 at 9:43 PM Justin Pryzby <pryzby@telsasoft.com>
> wrote:
> > > This patch seems to be causing the planner to crash.
> > > Here's a query reduced from sqlsmith.
> > >
> > > | explain SELECT 1 FROM information_schema.constraint_column_usage
> WHERE 1 <= pg_trigger_depth();
> > >
> > > Program terminated with signal SIGSEGV, Segmentation fault.
> >
> > Reproduced.  Will look into this.
>
> I think the cause of this is that mark_async_capable_plan() failed to
> take into account that when the given path is a SubqueryScanPath or
> ForeignPath, the given corresponding plan might include a gating
> Result node that evaluates pseudoconstant quals.  My oversight.  :-(
> Attached is a patch for fixing that.  I think v14 has the same issue,
> so I think we need backpatching.
>
> Best regards,
> Etsuro Fujita
>
Hi,
Looking at the second hunk of the patch:
                FdwRoutine *fdwroutine = path->parent->fdwroutine;
...
+               if (IsA(plan, Result))
+                   return false;

It seems the check of whether plan is a Result node can be lifted ahead of
the switch statement (i.e. to the beginning of mark_async_capable_plan).

This way, we don't have to check for every case in the switch statement.

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.