Re: [Proposal] Expose internal MultiXact member count function for efficient monitoring

Xuneng Zhou <xunengzhou@gmail.com>

From: Xuneng Zhou <xunengzhou@gmail.com>

To: torikoshia <torikoshia@oss.nttdata.com>, Naga Appani <nagnrik@gmail.com>

Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Michael Paquier <michael@paquier.xyz>, Kirill Reshke <reshkekirill@gmail.com>, pgsql-hackers@postgresql.org

Date: 2025-10-17T02:10:12Z

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 →

Add pg_get_multixact_stats()
- 97b101776ce2 19 (unreleased) landed
Add MultiXactOffsetStorageSize() to multixact_internal.h
- 0e3ad4b96aed 19 (unreleased) landed
Change GetMultiXactInfo() to return the next multixact offset
- 9cf746a453c1 19 (unreleased) landed
Widen MultiXactOffset to 64 bits
- bd8d9c9bdfa0 19 (unreleased) cited
Refactor ReadMultiXactCounts() into GetMultiXactInfo()
- a977e419ee6e 19 (unreleased) landed
Move SQL-callable code related to multixacts into its own file
- df9133fa6384 19 (unreleased) landed
Split func.sgml into more manageable pieces
- 4e23c9ef65ac 19 (unreleased) cited

Attachments

v10-0001-Add-pg_get_multixact_stats-function-for-monitori.patch (application/octet-stream) patch v10-0001

Hi,

On Fri, Oct 17, 2025 at 8:28 AM torikoshia <torikoshia@oss.nttdata.com> wrote:
>
> On 2025-09-15 14:47, Naga Appani wrote:
>
> > With these updates in v9, I believe the patch is now in good shape to
> > be marked RFC. I’ll go ahead and update the CommitFest entry.
>
> As shown in the commitfest app, v9 patch fails to build:
>
>    multixactfuncs.c:129:28: error: call to undeclared function
> 'heap_form_tuple'; ISO C99 and later do not support implicit function
> declarations [-Wimplicit-function-declaration]
>    129 |                 return
> HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls));
>        |                                          ^
>    multixactfuncs.c:129:28: note: did you mean 'brin_form_tuple'?
> ../../../../src/include/access/brin_tuple.h:96:19: note:
> 'brin_form_tuple' declared here
>     96 | extern BrinTuple *brin_form_tuple(BrinDesc *brdesc, BlockNumber
> blkno,
>        |                   ^
>    multixactfuncs.c:129:28: error: incompatible integer to pointer
> conversion passing 'int' to parameter of type 'const HeapTupleData *'
> (aka 'const struct HeapTupleData *') [-Wint-conversion]
>    129 |                 return
> HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls));
>        |
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    ../../../../src/include/funcapi.h:230:40: note: passing argument to
> parameter 'tuple' here
>    230 | HeapTupleGetDatum(const HeapTupleData *tuple)
>        |                                        ^
>    2 errors generated.
>
> Could you please update the patch to fix this?

Here’s the updated v10 patch, now including access/htup_details.h in
src/backend/utils/adt/multixactfuncs.c. I’m also interested in this
patch and plan to review it.

Best,
Xuneng