From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Himanshu Upadhyaya <upadhyaya(dot)himanshu(at)gmail(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Aleksander Alekseev <aleksander(at)timescale(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: HOT chain validation in verify_heapam() |
Date: | 2022-11-17 17:53:52 |
Message-ID: | 20221117175352.okhfekc7b6aymmra@awork3.anarazel.de |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Hi,
On 2022-11-17 21:33:17 +0530, Himanshu Upadhyaya wrote:
> 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?
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
From | Date | Subject | |
---|---|---|---|
Next Message | Andres Freund | 2022-11-17 18:37:49 | Re: TAP output format in pg_regress |
Previous Message | Tom Lane | 2022-11-17 17:51:28 | Re: CREATE UNLOGGED TABLE seq faults when debug_discard_caches=1 |