Horton

Re: pg_stat_database.checksum_failures vs shared relations

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, pgsql-hackers@postgresql.org, Magnus Hagander <magnus@hagander.net>, Julien Rouhaud <rjuju123@gmail.com>
Date: 2025-03-28T00:44:58Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix mis-attribution of checksum failure stats to the wrong database

  2. Return NULL for checksum failures if checksums are not enabled

  3. Show shared object statistics in pg_stat_database

On Thu, Mar 27, 2025 at 12:06:45PM -0400, Robert Haas wrote:
> On Thu, Mar 27, 2025 at 11:58 AM Andres Freund <andres@anarazel.de> wrote:
> > So, today we have the weird situation that *some* checksum errors on shared
> > relations get attributed to the current database (if they happen in a backend
> > normally accessing a shared relation), whereas others get reported to the
> > "shared relations" "database" (if they happen during a base backup).  That
> > seems ... not optimal.
> >
> > One question is whether we consider this a bug that should be backpatched.
> 
> I think it would be defensible if pg_basebackup reported all errors
> with OID 0 and backend connections reported all errors with OID
> MyDatabaseId, but it seems hard to justify having pg_basebackup take
> care to report things using the correct database OID and individual
> backend connections not take care to do the same thing. So I think
> this is a bug. If fixing it in the back-branches is too annoying, I
> think it would be reasonable to fix it only in master, but
> back-patching seems OK too.

Being able to get a better reporting for shared relations in back
branches would be nice, but that's going to require some invasive
chirurgy, isn't it?

We don't know currently the OID of the relation whose block is
corrupted with only PageIsVerifiedExtended().  There are two callers
of PIV_REPORT_STAT on HEAD:
- The checksum reports from RelationCopyStorage() know the
SMgrRelation.
- ReadBuffersOperation() has an optional Relation and a
SMgrRelationData.

We could just refactor PageIsVerifiedExtended() so as it reports a
state about why the verification failed and let the callers report the
checksum failure with a relation OID, splitting the data for shared
and non-shared relations? 
--
Michael