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

On Sun, Apr 10, 2022 at 7:41 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:

> On Sun, Apr 10, 2022 at 07:43:48PM +0900, Etsuro Fujita 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.
>
> Thanks - this seems to resolve the issue.
>
> On Sun, Apr 10, 2022 at 06:46:25AM -0700, Zhihong Yu wrote:
> > 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.
>
> I think you misread it - the other branch says: if (*not* IsA())
>
> No, I didn't misread:

if (!IsA(plan, Result) &&
mark_async_capable_plan(plan,
((ProjectionPath *) path)->subpath))
return true;
return false;

If the plan is Result node, false would be returned.
So the check can be lifted to the beginning of the func.

Cheers