Re: HOT chain validation in verify_heapam()

On Tue, Nov 15, 2022 at 3:32 AM Andres Freund <andres(at)anarazel(dot)de> wrote:

>
> > Furthermore, it is
> > possible that successor[x] = successor[x'] since the page might be
> corrupted
> > and we haven't checked otherwise.
> >
> > predecessor[y] = x means that successor[x] = y but in addition we've
> > checked that y is sane, and that x.xmax=y.xmin. If there are multiple
> > tuples for which these conditions hold, we've issued complaints about
> > all but one and entered the last into the predecessor array.
>
> As shown by the isolationtester test I just posted, this doesn't quite work
> right now. Probably fixable.
>
> I don't think we can follow non-HOT ctid chains if they're older than the
> xmin
> horizon, including all cases of xmin being frozen. There's just nothing
> guaranteeing that the tuples are actually "related".
>
> I understand the problem with frozen tuples but don't understand the
concern with non-HOT chains,
could you please help with some explanation around it?

--
Regards,
Himanshu Upadhyaya
EnterpriseDB: http://www.enterprisedb.com