Horton

Re: POC: make mxidoff 64 bits

Maxim Orlov <orlovmg@gmail.com>

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From: Maxim Orlov <orlovmg@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: wenhui qiu <qiuwenhuifx@gmail.com>, Alexander Korotkov <aekorotkov@gmail.com>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-12-27T17:09:56Z
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 partial read handling in pg_upgrade's multixact conversion

  2. Increase timeout in multixid_conversion upgrade test

  3. Improve sanity checks on multixid members length

  4. Clarify comment on multixid offset wraparound check

  5. Never store 0 as the nextMXact

  6. Add runtime checks for bogus multixact offsets

  7. Widen MultiXactOffset to 64 bits

  8. Move pg_multixact SLRU page format definitions to a separate header

  9. Convert confusing macros in multixact.c to static inline functions

  10. Index SLRUs by 64-bit integers rather than by 32-bit integers

  11. Cope with possible failure of the oldest MultiXact to exist.

Attachments

On Wed, 18 Dec 2024 at 13:21, Heikki Linnakangas <hlinnaka@iki.fi> wrote:

>
> Attached is some more cleanup on top of patch set v9, removing more dead
> stuff related to wraparound. I also removed the oldestOffsetKnown
> variable and related code. It was needed to deal with clusters upgraded
> from buggy 9.3 and 9.4 era versions, but now that pg_upgrade will
> rewrite the SLRUs, it's no longer needed.
>
Yep, multixact.c looks correct to me. As for "XXX could use
SimpleLruTruncate()", yes, for sure.
Actually, xl_multixact_truncate.startTruncMemb is also no longer needed, is
it?


> Does the pg_upgrade code work though, if you have that buggy situation
> where oldestOffsetKnown == false ?
>
> >
> >               if (!TransactionIdIsValid(*xactptr))
> >               {
> >                       /* Corner case 3: we must be looking at unused
> slot zero */
> >                       Assert(offset == 0);
> >                       continue;
> >               }
>
> After upgrade, this corner case 3 would *not* happen on offset == 0. So
> looks like we're still missing test coverage for this upgrade corner case.
>
Am I understanding correctly that you want to have a test corresponding to
the buggy 9.3 and 9.4 era versions?
Do you think we could imitate this scenario on a current master branch like
that:
1) generate a couple of offsets segments for the first table;
2) generate more segments for a second table;
3) drop first table;
4) stop pg cluster;
5) remove pg_multixact/offsets/0000
6) upgrade?

PFA, v10-0016-TEST-try-to-replicate-buggy-oldest-offset.patch
This test will fail now, for an obvious reason, but is this case a relevant
one?

-- 
Best regards,
Maxim Orlov.