Re: POC: make mxidoff 64 bits

Heikki Linnakangas <hlinnaka@iki.fi>

From: Heikki Linnakangas <hlinnaka@iki.fi>

To: Maxim Orlov <orlovmg@gmail.com>, Postgres hackers <pgsql-hackers@lists.postgresql.org>

Date: 2024-04-23T09:37:40Z

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 →

Fix partial read handling in pg_upgrade's multixact conversion
- ac94ce8194e5 19 (unreleased) landed
Increase timeout in multixid_conversion upgrade test
- bd43940b02b2 19 (unreleased) landed
Improve sanity checks on multixid members length
- ecb553ae8211 19 (unreleased) landed
Clarify comment on multixid offset wraparound check
- 170361d7b869 14.21 landed
- b0b52b7123ae 15.16 landed
- 7d42e2367c6b 16.12 landed
- cd1a887fe9bf 17.8 landed
- 3fbad030a24d 18.2 landed
- 366dcdaf5779 19 (unreleased) landed
Never store 0 as the nextMXact
- 87a350e1f284 19 (unreleased) landed
Add runtime checks for bogus multixact offsets
- d4b7bde4183b 19 (unreleased) landed
Widen MultiXactOffset to 64 bits
- bd8d9c9bdfa0 19 (unreleased) landed
Move pg_multixact SLRU page format definitions to a separate header
- bb3b1c4f6462 19 (unreleased) landed
Convert confusing macros in multixact.c to static inline functions
- 0099b9408e8c 17.0 landed
Index SLRUs by 64-bit integers rather than by 32-bit integers
- 4ed8f0913bfd 17.0 cited
Cope with possible failure of the oldest MultiXact to exist.
- b6a3444fa635 9.4.4 cited

On 23/04/2024 11:23, Maxim Orlov wrote:
> PROPOSAL
> Make multixact offsets 64 bit.

+1, this is a good next step and useful regardless of 64-bit XIDs.

> @@ -156,7 +148,7 @@
>  		((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
>  
>  /* page in which a member is to be found */
> -#define MXOffsetToMemberPage(xid) ((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
> +#define MXOffsetToMemberPage(xid) ((xid) / (MultiXactOffset) MULTIXACT_MEMBERS_PER_PAGE)
>  #define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) / SLRU_PAGES_PER_SEGMENT)
>  
>  /* Location (byte offset within page) of flag word for a given member */

This is really a bug fix. It didn't matter when TransactionId and 
MultiXactOffset were both typedefs of uint32, but it was always wrong. 
The argument name 'xid' is also misleading.

I think there are some more like that, MXOffsetToFlagsBitShift for example.

-- 
Heikki Linnakangas
Neon (https://neon.tech)