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

On Sun, Apr 10, 2022 at 3:42 AM Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com>
wrote:

> On Sat, Apr 9, 2022 at 1:58 AM Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com>
> wrote:
> > On Fri, Apr 8, 2022 at 9:43 PM Justin Pryzby <pryzby(at)telsasoft(dot)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