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help / color / mirror / Atom feedFrom: Shinya Kato <[email protected]>
To: Fujii Masao <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: pg_stat_replication.*_lag sometimes shows NULL during active replication
Date: Thu, 19 Mar 2026 22:58:18 +0900
Message-ID: <CAOzEurRV117N2neo1N_O+xWPv=-R7qou+i7k-h79JjTP9sO1Fg@mail.gmail.com> (raw)
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On Tue, Mar 17, 2026 at 11:00 AM Fujii Masao <[email protected]> wrote:
>
> On Mon, Mar 16, 2026 at 9:26 AM Shinya Kato <[email protected]> wrote:
> > Thank you for the v4 patch. I think this approach is better than mine.
> > I tested the patch and confirmed that the issue no longer reproduces
> > with physical replication. However, with logical replication, the lag
> > columns in pg_stat_replication still show NULL periodically at
> > wal_receiver_status_interval, since send_feedback() in worker.c can
> > still send duplicate positions.
>
> I was thinking that if a feedback message triggered by
> wal_receiver_status_interval has the same LSNs as the previous message,
> it's expected for the lag columns to become NULL. But you see it differently,
> don't you? Sorry, I failed to understand your point...
Sorry for the confusion. I ran a script inserting one row every 0.5
seconds under logical replication and confirmed that NULL still
appears in the lag columns even while replication is actively running.
I was initially mistaken that this was tied to
wal_receiver_status_interval timing — that turned out to be unrelated.
I haven't had time to investigate further, but my current impression
is that the existing approach may not be sufficient for logical
replication.
--
Best regards,
Shinya Kato
NTT OSS Center
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Subject: Re: pg_stat_replication.*_lag sometimes shows NULL during active replication
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