> 29 авг. 2020 г., в 00:56, Robert Haas <[email protected]> написал(а):
>
> On Fri, Aug 28, 2020 at 2:10 PM Andrey M. Borodin <[email protected]>
> 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 (while toast 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 the thread nearby. Yet I cannot fix the
problem, because cannot list affected tuples. These tools do not solve the
problem neglected 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.
