Re: pg_amcheck contrib application

> On Mar 17, 2021, at 9:00 PM, Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> wrote:
>
> Of the toast pointer fields:
>
> int32 va_rawsize; /* Original data size (includes header) */
> int32 va_extsize; /* External saved size (doesn't) */
> Oid va_valueid; /* Unique ID of value within TOAST table */
> Oid va_toastrelid; /* RelID of TOAST table containing it */
>
> all seem worth getting as part of any toast error message, even if these fields themselves are not corrupt. It just makes it easier to understand the context of the error you're looking at. At first I tried putting these into each message, but it is very wordy to say things like "toast pointer with rawsize %u and extsize %u pointing at relation with oid %u" and such. It made more sense to just add these four fields to the verify_heapam tuple format. That saves putting them in the message text itself, and has the benefit that you could filter the rows coming from verify_heapam() for ones where valueid is or is not null, for example. This changes the external interface of verify_heapam, but I didn't bother with a amcheck--1.3--1.4.sql because amcheck--1.2--1.3. sql was added as part of the v14 development work and has not yet been released. My assumption is that I can just change it, rather than making a new upgrade file.
>
> These patches fix the visibility rules and add extra toast checking.

These new patches address the same issues as v9 (which was never committed), and v10 (which was never even posted to this list), with some changes.

Rather than print out all four toast pointer fields for each toast failure, va_rawsize, va_extsize, and va_toastrelid are only mentioned in the corruption message if they are related to the specific corruption. Otherwise, just the va_valueid is mentioned in the corruption message.

The visibility rules fix is different in v11, relying on a visibility check which more closely follows the implementation of HeapTupleSatisfiesVacuumHorizon.