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doc: clarify how logical replication takes its initial snapshot

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Reported-by: Koen De Groote

Discussion: https://postgr.es/m/171606613152.686.7693963105919927503@wrigleys.postgresql.org

Backpatch-through: master
This commit is contained in:
Bruce Momjian 2024-11-21 17:14:33 -05:00
parent 53dcba9be5
commit 4c4aaa19a6
1 changed files with 6 additions and 14 deletions
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20
doc/src/sgml/logical-replication.sgml
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@ -24,10 +24,11 @@
</para> </para>
<para> <para>
Logical replication of a table typically starts with taking a snapshot When logical replication of a table typically starts, PostgreSQL takes
of the data on the publisher database and copying that to the subscriber. a snapshot of the table's data on the publisher database and copies it
Once that is done, the changes on the publisher are sent to the subscriber to the subscriber. Once complete, changes on the publisher since the
as they occur in real-time. The subscriber applies the data in the same initial copy are sent continually to the subscriber. The subscriber
applies the data in the same
order as the publisher so that transactional consistency is guaranteed for order as the publisher so that transactional consistency is guaranteed for
publications within a single subscription. This method of data replication publications within a single subscription. This method of data replication
is sometimes referred to as transactional replication. is sometimes referred to as transactional replication.
@ -165,7 +166,7 @@
The individual tables can be added and removed dynamically using The individual tables can be added and removed dynamically using
<link linkend="sql-alterpublication"><command>ALTER PUBLICATION</command></link>. Both the <literal>ADD <link linkend="sql-alterpublication"><command>ALTER PUBLICATION</command></link>. Both the <literal>ADD
TABLE</literal> and <literal>DROP TABLE</literal> operations are TABLE</literal> and <literal>DROP TABLE</literal> operations are
transactional; so the table will start or stop replicating at the correct transactional, so the table will start or stop replicating at the correct
snapshot once the transaction has committed. snapshot once the transaction has committed.
</para> </para>
</sect1> </sect1>
@ -1954,15 +1955,6 @@ CONTEXT: processing remote data for replication origin "pg_16395" during "INSER
<sect1 id="logical-replication-architecture"> <sect1 id="logical-replication-architecture">
<title>Architecture</title> <title>Architecture</title>
<para>
Logical replication starts by copying a snapshot of the data on the
publisher database. Once that is done, changes on the publisher are sent
to the subscriber as they occur in real time. The subscriber applies data
in the order in which commits were made on the publisher so that
transactional consistency is guaranteed for the publications within any
single subscription.
</para>
<para> <para>
Logical replication is built with an architecture similar to physical Logical replication is built with an architecture similar to physical
streaming replication (see <xref linkend="streaming-replication"/>). It is streaming replication (see <xref linkend="streaming-replication"/>). It is