Date: Sun, 10 Apr 2022 21:41:01 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Etsuro Fujita <etsuro.fujita@gmail.com>, 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>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: Defer selection of asynchronous subplans until the executor
 initialization stage
Message-ID: <20220411024101.GC26620@telsasoft.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALNJ-vRF1fw9dh-2sZW9bETqwcttOMw4ptLp6sOrzVUSw=Ycvw@mail.gmail.com>
 <CAPmGK15NkuaVo0Fu_0TfoCpPPJaJi4OMLzEQtkE6Bt6YT52fPQ@mail.gmail.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Archived-At: <https://www.postgresql.org/message-id/20220411024101.GC26620%40telsasoft.com>
Precedence: bulk

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.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.

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())

-- 
Justin