Horton

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

Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>

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From: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
To: Naga Appani <nagnrik@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>, Xuneng Zhou <xunengzhou@gmail.com>, torikoshia <torikoshia@oss.nttdata.com>, Michael Paquier <michael@paquier.xyz>, Kirill Reshke <reshkekirill@gmail.com>, pgsql-hackers@postgresql.org
Date: 2025-12-08T04:40:16Z
Lists: pgsql-hackers 
On Sat, Dec 6, 2025 at 11:23 PM Naga Appani <nagnrik@gmail.com> wrote:
>
> Hi Ashutosh,
>
> Thanks for the review!
>
> I agree - comparing the exposed members_size against the documented
> thresholds is sufficient for monitoring purposes.
>
> This aligns with the approach taken in v11: exposing the current usage in
> a way consistent with other PostgreSQL counters (e.g., XIDs, OIDs), without
> introducing user-visible remaining-capacity calculations whose behavior is
> inconsistent and difficult to interpret externally. In the same spirit, I
> removed oldest_offset: as we discussed, it is internal and does not
> provide an actionable signal to users.
>
> If this addresses the concerns raised so far, I would appreciate
> consideration in moving v11 forward for commit.

The patch at [1] changes the function used to fetch mxid related
information. With that we will get rid of awkwardness around
non-availability of the statistics. It's better to wait for those
changes to get committed before moving this forward.

-- 
Best Wishes,
Ashutosh Bapat