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From: Mark Dilger <mark.dilger@enterprisedb.com>
To: Andrey M. Borodin <x4mmm@yandex-team.ru>
Cc: Amul Sul <sulamul@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: new heapcheck contrib module
Date: Fri, 28 Aug 2020 08:12:44 -0700
Message-ID: <D8186B59-3A44-4E2F-AC9B-BD7DA6EC06B0@enterprisedb.com> (raw)
In-Reply-To: <47D0EC13-0B9A-4D97-9435-0846B0DA2916@yandex-team.ru>
References: <12ED3DA8-25F0-4B68-937D-D907CFBF08E7@enterprisedb.com>
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	<47D0EC13-0B9A-4D97-9435-0846B0DA2916@yandex-team.ru>



> On Aug 27, 2020, at 10:07 PM, Andrey M. Borodin <x4mmm@yandex-team.ru> wrote:
> 
> 
> 
>> 25 авг. 2020 г., в 19:36, Mark Dilger <mark.dilger@enterprisedb.com> написал(а):
> 
> Hi Mark!
> 
> Thanks for working on this important feature.
> 
> I was experimenting a bit with our internal heapcheck and found out that it's not helping with truncated CLOG anyhow.
> Will your module be able to gather tid's of similar corruptions?
> 
> server/db M # select * from heap_check('pg_toast.pg_toast_4848601');
> ERROR:  58P01: could not access status of transaction 636558742
> DETAIL:  Could not open file "pg_xact/025F": No such file or directory.
> LOCATION:  SlruReportIOError, slru.c:913
> Time: 3439.915 ms (00:03.440)

The design principle for verify_heapam.c is, if the rest of the system is not corrupt, corruption in the table being checked should not cause a crash during the table check. This is a very limited principle.  Even corruption in the associated toast table or toast index could cause a crash.  That is why checking against the toast table is optional, and false by default.

Perhaps a more extensive effort could be made later.  I think it is out of scope for this release cycle.  It is a very interesting area for further research, though.

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company








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