Re: new heapcheck contrib module

> On Aug 27, 2020, at 10:07 PM, Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
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>
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>> 25 авг. 2020 г., в 19:36, Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> написал(а):
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> 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