Hi, On 2022-11-17 21:33:17 +0530, Himanshu Upadhyaya wrote: > On Tue, Nov 15, 2022 at 3:32 AM Andres Freund <and...@anarazel.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?
I think there might be cases where following non-HOT ctid-chains across tuples within a page will trigger spurious errors, if the tuple versions are older than the xmin horizon. But it's a bit hard to say without seeing the code with a bunch of the other bugs fixed. Greetings, Andres Freund
