Horton

Re: new heapcheck contrib module

x4mmm@yandex-team.ru

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From: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, Amul Sul <sulamul@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Geoghegan <pg@bowt.ie>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2020-08-29T10:27:03Z
Lists: pgsql-hackers 

> 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 (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.

Commits

  1. Add pg_amcheck, a CLI for contrib/amcheck.

  2. Refactor and generalize the ParallelSlot machinery.

  3. Generalize parallel slot result handling.

  4. Move some code from src/bin/scripts to src/fe_utils to permit reuse.

  5. Factor pattern-construction logic out of processSQLNamePattern.

  6. Doc: clean up verify_heapam() documentation.

  7. Fix more portability issues in new amcheck code.

  8. Fix portability issues in new amcheck test.

  9. Try to avoid a compiler warning about using fxid uninitialized.

  10. Extend amcheck to check heap pages.

  11. Adjust walsender usage of xlogreader, simplify APIs

  12. Improve checking of child pages in contrib/amcheck.

  13. Sanitize line pointers within contrib/amcheck.

  14. Fix possible sorting error when aborting use of abbreviated keys.