Re: [PATCH] Add pg_current_vxact_id() function to expose virtual transaction IDs

Hi Pavlo, Robert,

Responding to both of you in one mail since the points are related.

== To Pavlo, on v3 ==

On Thu, Feb 5, 2026 at 10:13 AM Pavlo Golub <pavlo.golub@cybertec.at> wrote:
> I've prepared v3 of the patch addrressing Henson's code review:
> - Added #define VXID_FMT "%d/%u" to lock.h
> - Updated lockfuncs.c, elog.c, and xid8funcs.c to use it
> - Use "localXID" (not "localTransactionId") in user docs

Thanks.  All three items from my v2 review are addressed in v3:

  1. VXID_FMT macro                 -- OK
  2. VXID_FMT applied to 3 files    -- OK
  3. "localXID" in func-info.sgml   -- OK

The patch applies cleanly on master and "make check-world" passes on
my machine (macOS/arm64).

> My main concern though is about semantic clarity. I see a huge problem
> that one needs to query pg_locks to get VXID. Why would I want to
> query the lock subsystem to get transaction ID? That's very confusing.

Agreed.  The asymmetry with pg_backend_pid() / pg_current_xact_id() is
the part I find most persuasive too -- regardless of performance,
having to enter the lock subsystem to ask "what is my transaction's
identity?" is an odd shape for the API.

== To Robert ==

On Sat, Feb 14, 2026 at 2:16 AM Robert Haas <robertmhaas@gmail.com> wrote:
> I agree with this and would be inclined to accept the patch. I have
> reviewed the v3 patch and I didn't see anything wrong with it.

Thanks for taking a look.  I'll leave the empirical side of the
performance argument to Pavlo if he wants to follow up on it; my own
endorsement rests mainly on the API-shape point above.

== One nit on v3 ==

Running src/tools/pgindent/pgindent over the touched C/H files
produces one small rewrap in xid8funcs.c (no semantic change, just a
comment reflow):

    - * Check if we have a valid vxid.  The vxid format matches what's used
    - * in elog.c for the %v placeholder and in pg_locks.virtualtransaction.
    + * Check if we have a valid vxid.  The vxid format matches what's used
in
    + * elog.c for the %v placeholder and in pg_locks.virtualtransaction.

Pavlo, could you fold that into a v4?  Other than that I have nothing
more to add, and with v4 in place I would mark the patch Ready for
Committer.

Best regards,
Henson Choi