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Introduce a new GUC 'standby_slot_names'.

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This patch provides a way to ensure that physical standbys that are
potential failover candidates have received and flushed changes before
the primary server making them visible to subscribers. Doing so guarantees
that the promoted standby server is not lagging behind the subscribers
when a failover is necessary.

The logical walsender now guarantees that all local changes are sent and
flushed to the standby servers corresponding to the replication slots
specified in 'standby_slot_names' before sending those changes to the
subscriber.

Additionally, the SQL functions pg_logical_slot_get_changes,
pg_logical_slot_peek_changes and pg_replication_slot_advance are modified
to ensure that they process changes for failover slots only after physical
slots specified in 'standby_slot_names' have confirmed WAL receipt for those.

Author: Hou Zhijie and Shveta Malik
Reviewed-by: Masahiko Sawada, Peter Smith, Bertrand Drouvot, Ajin Cherian, Nisha Moond, Amit Kapila
Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com
This commit is contained in:
Amit Kapila
2024-03-08 08:10:45 +05:30
parent 453c468737
commit bf279ddd1c
18 changed files with 918 additions and 27 deletions
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12
doc/src/sgml/logicaldecoding.sgml
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@@ -384,6 +384,18 @@ postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NU
must be enabled on the standby. It is also necessary to specify a valid
<literal>dbname</literal> in the
<link linkend="guc-primary-conninfo"><varname>primary_conninfo</varname></link>.
It's highly recommended that the said physical replication slot is named in
<link linkend="guc-standby-slot-names"><varname>standby_slot_names</varname></link>
list on the primary, to prevent the subscriber from consuming changes
faster than the hot standby. Even when correctly configured, some latency
is expected when sending changes to logical subscribers due to the waiting
on slots named in
<link linkend="guc-standby-slot-names"><varname>standby_slot_names</varname></link>.
When <varname>standby_slot_names</varname> is utilized, the
primary server will not completely shut down until the corresponding
standbys, associated with the physical replication slots specified
in <varname>standby_slot_names</varname>, have confirmed
receiving the WAL up to the latest flushed position on the primary server.
</para>
<para>