Horton

Re: POC: make mxidoff 64 bits

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Pavel Borisov <pashkin.elfe@gmail.com>
Cc: Maxim Orlov <orlovmg@gmail.com>, Alexander Korotkov <aekorotkov@gmail.com>, wenhui qiu <qiuwenhuifx@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-09-12T13:14:08Z
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.

On 2024-Sep-12, Pavel Borisov wrote:

> Hi, Maxim!
> 
> Previously we accessed offsets in shared MultiXactState without locks as
> 32-bit read is always atomic. But I'm not sure it's so when offset become
> 64-bit.
> E.g. GetNewMultiXactId():
> 
> nextOffset = MultiXactState->nextOffset;
> is outside lock.

Good though.  But fortunately I think it's not a problem.  The one you
say is with MultiXactGetLock held in shared mode -- and that works OK,
as the assignment (in line 1263 at the bottom of the same routine) is
done with exclusive lock held.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/