Horton

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

Fujii Masao <masao.fujii@gmail.com>

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From: Fujii Masao <masao.fujii@gmail.com>
To: Shinya Kato <shinya11.kato@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2026-03-25T15:30:42Z
Lists: pgsql-hackers

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On Wed, Mar 25, 2026 at 4:03 PM Shinya Kato <shinya11.kato@gmail.com> wrote:
> Thanks for the updated patch. LGTM.
>
> Regarding the backpatch, I'd personally appreciate it if the walsender.c changes were backpatched to stable branches. As you noted, it don't fully solve the reported issue, but they do help reduce the cases where lag columns in pg_stat_replication unexpectedly become NULL.
>
> Even a partial mitigation in the back branches would be valuable for users running stable releases.

+1

I've split the changes into two patches.

Patch 0001 fixes premature NULL lag reporting in walsender. I will commit it
and backpatch it to all supported branches.

Patch 0002 avoids sending duplicate WAL locations in standby status replies.
I will commit this to master only.

Regards,

-- 
Fujii Masao

Commits

  1. Avoid sending duplicate WAL locations in standby status replies

  2. Fix premature NULL lag reporting in pg_stat_replication