Re: new heapcheck contrib module

> 29 авг. 2020 г., в 00:56, Robert Haas <robertmhaas@gmail.com> написал(а):
>
> On Fri, Aug 28, 2020 at 2:10 PM Andrey M. Borodin <x4mmm@yandex-team.ru> wrote:
>> I don't think so. ISTM It's the same problem of xmax<relfrozenxid actually, just hidden behind detoasing.
>> Our regular heap_check was checking xmin\xmax invariants for tables, but failed to recognise the problem in toast
(whiletoast was accessible until CLOG truncation). 
>
> The code can (and should, and I think does) refrain from looking up
> XIDs that are out of the range thought to be valid -- but how do you
> propose that it avoid looking up XIDs that ought to have clog data
> associated with them despite being >= relfrozenxid and < nextxid?
> TransactionIdDidCommit() does not have a suppress-errors flag, adding
> one would be quite invasive, yet we cannot safely perform a
> significant number of checks without knowing whether the inserting
> transaction committed.

What you write seems completely correct to me. I agree that CLOG thresholds lookup seems unnecessary.

But I have a real corruption at hand (on testing site). If I have proposed here heapcheck. And I have pg_surgery from
thethread nearby. Yet I cannot fix the problem, because cannot list affected tuples. These tools do not solve the
problemneglected for long enough. It would be supercool if they could. 

This corruption like a caries had 3 stages:
1. incorrect VM flag that page do not need vacuum
2. xmin and xmax < relfrozenxid
3. CLOG truncated

Stage 2 is curable with proposed toolset, stage 3 is not. But they are not that different.

Thanks!

Best regards, Andrey Borodin.