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From: Fujii Masao <[email protected]>
To: Shinya Kato <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: pg_stat_replication.*_lag sometimes shows NULL during active replication
Date: Tue, 17 Mar 2026 11:00:38 +0900
Message-ID: <CAHGQGwFzg9J_z71kwnjXOxaoO3upMW8RdT4ieE8MBLq6h-ojZg@mail.gmail.com> (raw)
In-Reply-To: <CAOzEurSDzFsRXjofhq7mbNgoL8HaVbNeEhWBm7m9_K2ZNQnaBw@mail.gmail.com>
References: <CAOzEurTzcUrEzrH97DD7+Yz=HGPU81kzWQonKZvqBwYhx2G9_A@mail.gmail.com>
	<CAHGQGwE=kyQ+YnGPn8zpZ959+3ywg8OR_Nu__uXxxuE0E+Y_Zg@mail.gmail.com>
	<CAOzEurRGiGE2Dfe+ySpb=+93ku=7ZC6RgAbHtLC6Xsq3g2XexA@mail.gmail.com>
	<CAHGQGwH2h_R7FWPvEs3+NWLwHZoj9r96tUyRKi5haqxMc6FXiQ@mail.gmail.com>
	<CAOzEurQiP3uebd1GMiC1Dzf5VJwF4ZBEpJ6QYQFE6Y+rVjxqNA@mail.gmail.com>
	<CAHGQGwEmMBBAE0RG-R3_LacfT4fbB55qGE6n9O5mNwrqvbNBtw@mail.gmail.com>
	<CAOzEurRF+OWcMZpfE=NV_Wcm6CFFGOnuxC6L9WWCjOMN0_eZMQ@mail.gmail.com>
	<CAHGQGwGPg20Rw2PydBDXiKHgn55s--E14-qRy7t3M+DHreCJww@mail.gmail.com>
	<CAOzEurSDzFsRXjofhq7mbNgoL8HaVbNeEhWBm7m9_K2ZNQnaBw@mail.gmail.com>

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...

Regards,

-- 
Fujii Masao





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