Re: Assertion failure in SnapBuildInitialSnapshot()

On Thu, Nov 17, 2022 at 11:15 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2022-11-17 10:44:18 +0530, Amit Kapila wrote:
> > On Wed, Nov 16, 2022 at 11:56 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > On 2022-11-16 14:22:01 +0530, Amit Kapila wrote:
> > > > On Wed, Nov 16, 2022 at 7:30 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > > > On 2022-11-15 16:20:00 +0530, Amit Kapila wrote:
> > > > > > On Tue, Nov 15, 2022 at 8:08 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > I don't think that'd catch a catalog snapshot. But perhaps the better answer
> > > for the catalog snapshot is to just invalidate it explicitly. The user doesn't
> > > have control over the catalog snapshot being taken, and it's not too hard to
> > > imagine the walsender code triggering one somewhere.
> > >
> > > So maybe we should add something like:
> > >
> > > InvalidateCatalogSnapshot(); /* about to overwrite MyProc->xmin */
> > >
> >
> > The comment "/* about to overwrite MyProc->xmin */" is unclear to me.
> > We already have a check (/* so we don't overwrite the existing value
> > */
> > if (TransactionIdIsValid(MyProc->xmin))) in SnapBuildInitialSnapshot()
> > which ensures that we don't overwrite MyProc->xmin, so the above
> > comment seems contradictory to me.
>
> The point is that catalog snapshots could easily end up setting MyProc->xmin,
> even though the caller hasn't done anything wrong. So the
> InvalidateCatalogSnapshot() would avoid erroring out in a number of scenarios.
>

Okay, updated the patch accordingly.

--
With Regards,
Amit Kapila.