RE: Forget close an open relation in ReorderBufferProcessTXN()

On Saturday, April 17, 2021 4:13 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Sat, Apr 17, 2021 at 12:05 PM Japin Li <japinli@hotmail.com> wrote:
> >
> > On Sat, 17 Apr 2021 at 14:09, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> > > On Thu, Apr 15, 2021 at 4:53 PM Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> > >>
> > >> On Thu, Apr 15, 2021 at 4:00 PM Japin Li <japinli@hotmail.com> wrote:
> > >> >
> > >> > The RelationIdGetRelation() comment says:
> > >> >
> > >> > > Caller should eventually decrement count. (Usually, that
> > >> > > happens by calling RelationClose().)
> > >> >
> > >> > However, it doesn't do it in ReorderBufferProcessTXN().
> > >> > I think we should close it, here is a patch that fixes it. Thoughts?
> > >> >
> > >>
> > >> +1. Your fix looks correct to me but can we test it in some way?
> > >>
> > >
> > > I have tried to find a test but not able to find one. I have tried
> > > with a foreign table but we don't log truncate for it, see
> > > ExecuteTruncate. It has a check that it will log for relids where
> > > RelationIsLogicallyLogged. If that is the case, it is not clear to
> > > me how we can ever hit this condition? Have you tried to find the test?
> >
> > I also don't find a test for this.  It is introduced in 5dfd1e5a6696,
> > wrote by Simon Riggs, Marco Nenciarini and Peter Eisentraut.  Maybe
> > they can explain when we can enter this condition?
> 
> My guess is that this has been copied from the code a few lines above to
> handle insert/update/delete where it is required to handle some DDL ops like
> Alter Table but I think we don't need it here (for Truncate op). If that
> understanding turns out to be true then we should either have an Assert for
> this or an elog message.
In this thread, we are discussing 3 topics below...

(1) necessity of the check for REORDER_BUFFER_CHANGE_TRUNCATE in ReorderBufferProcessTXN()
(2) discussion of whether we disallow decoding of operations on user catalog tables or not
(3) memory leak of maybe_send_schema() (patch already provided)

Let's address those one by one.
In terms of (1), which was close to the motivation of this thread,
first of all, I traced the truncate processing
and I think the check is done by truncate command side as well.
I preferred Assert rather than never called elog,
but it's OK to choose elog if someone has strong opinion on it.
Attached the patch for this.

Best Regards,
	Takamichi Osumi