Thread

Re: could sent_lsn be lower than write/flush/replay_lsn?

Jaime Casanova <jcasanov@systemguards.com.ec> — 2025-12-31T01:42:16Z

On Mon, Dec 29, 2025 at 2:13 AM Ashutosh Bapat
<ashutosh.bapat.oss@gmail.com> wrote:
>
> On Sat, Dec 27, 2025 at 1:18 PM cca5507 <2624345507@qq.com> wrote:
> >
> > The sent_lsn is just where the wal sender currently reading, so it could be lower than
> > write/flush/replay_lsn.
>
> +1.
>
> I guess, the logical replication is restarting in a loop. If that's
> the case, you will find multiple errors happening in the loop. Another
> guess is it's because of the walsender/receiver timeout. Do you see
> timeout error from the corresponding background workers? What's
> downstream?
>

Thanks both of you for clarifying this, it was actually a timeout
error. It seems for some reason all the subscriber got disconnected
from provider and for a problem we had some years ago (when using
pglogical in this same customer) wal_sender_timeout was set to 1
hour... which AFAIU made the wal_sender process keep active for 1 hour
while the subscriber tried to reconnect ans saw a walsender already
connected to another (the oldest already died) PID.

We returned wal_sender_timeout to its original value and everything
started to flow...


-- 
Jaime Casanova
SYSTEMGUARDS S.A.