Subject: Re[2]: [PATCH] Add pg_current_vxact_id() function to expose virtual transaction IDs

From: "Pavlo Golub" <[email-masked]>
Date: Tue, 06 Jan 2026 13:32:16 +0000

Hello.

Thanks for the review.

>
>Only pg_locks has it. And you can already get your VXID from there:
>
>   SELECT virtualtransaction FROM pg_locks
>   WHERE pid = pg_backend_pid() LIMIT 1;
While it is true that pg_locks contains the virtual transaction 
information, I believe there are strong technical reasons to expose this 
directly via a function.
First of all, querying pg_locks is expensive. By contrast, 
pg_current_vxact_id() is a practically free O(1) read from MyProc.
The %v log placeholder is the specific identifier for individual 
transaction executions (including read-only ones where no permanent XID 
is assigned). PIDs (%p) are session-scoped and too coarse for helping 
debug specific transactions in connection-pooled environments. This 
function allows applications to easily obtain the ID needed to correlate 
with server logs.
We already provide fast accessors for other identifiers like 
pg_backend_pid() and pg_current_xact_id(). Additionally, PostgreSQL 
often provides utility functions that overlap with other commands or 
views to improve developer experience (e.g., pg_notify() vs NOTIFY, 
pg_sleep() vs pg_sleep_for() vs pg_sleep_until()). It feels consistent 
to offer a simple accessor rather than requiring a complex query against 
a system view.

Best regards,
Pavlo Golub

---

From: Henson Choi <[email-masked]>
Date: Fri, 9 Jan 2026 09:03:55 +0900

Hi Pavlo,

> information, I believe there are strong technical reasons to expose this

Agreed.

> pg_current_vxact_id() is a practically free O(1) read from MyProc.

Yes, this is a significant advantage. The function simply reads from
MyProc without any locking or iteration.

> function allows applications to easily obtain the ID needed to correlate

This is a compelling use case. In connection-pooled environments,
correlating application-side logs with server logs by VXID is much
more precise than using PIDs.

> to offer a simple accessor rather than requiring a complex query against
I agree. This follows established PostgreSQL patterns.

> Pavlo Golub
Additionally, the implementation is minimal (~20 lines), so the binary
size impact is negligible. And since it's a leaf function called only
when explicitly invoked by users, it has no impact on the main code
path performance.

Best regards,
Henson