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Subject: Re: Replication slot WAL reservation
From: Christophe Pettus <xof@thebuild.com>
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Date: Tue, 25 Mar 2025 21:32:26 -0700
Cc: pgsql-general@postgresql.org
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To: Phillip Diffley <phillip6402@gmail.com>
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> On Mar 25, 2025, at 20:56, Phillip Diffley <phillip6402@gmail.com> =
wrote:
>=20
> Is there a message type that is used to confirm what logs have been =
successfully consumed?

You're looking for Standby Status Update:

	=
https://www.postgresql.org/docs/current/protocol-replication.html#PROTOCOL=
-REPLICATION-STANDBY-STATUS-UPDATE

The logical replication protocol is a superset of the binary replication =
protocol, so many of the same messages are used.

> The part I am uncertain about is what "after" means here, since LSNs =
are not presented in order, and the order of data streamed over the =
replication slot does not match the order of the data in the WAL.=20

I think there's a misunderstanding here (possibly my fault).  =
Transactions are always presented to the output plugin in commit order, =
and LSNs can be reliably used to determine the time ordering of commits. =
 LSNs are exactly what is used to determine how far into the WAL the =
replication slot has gotten.=