Horton

Re: pg_stat_replication.*_lag sometimes shows NULL during active replication

Shinya Kato <shinya11.kato@gmail.com>

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From: Shinya Kato <shinya11.kato@gmail.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-03-21T02:04:32Z
Lists: pgsql-hackers 
On Fri, Mar 20, 2026 at 2:13 AM Fujii Masao <masao.fujii@gmail.com> wrote:
> I think the issue occurs when the positions in the first message point to
> the same LSN (e.g., 0/030D5230), and the second message reports the same but
> larger LSN (e.g., 0/030D52E0).

Thanks for the explanation!

> I've updated the patch to address this. It removes fullyAppliedLastTime,
> tracks the positions from the previous reply, and clears the lag values only
> when the positions remain unchanged across two consecutive messages.
>
> Patch attached. Could you test and review this updated patch?

The patch works properly. I think it looks nice to me, except for the
typo I sent in the previous message.


-- 
Best regards,
Shinya Kato
NTT OSS Center

Commits

  1. Avoid sending duplicate WAL locations in standby status replies

  2. Fix premature NULL lag reporting in pg_stat_replication