pg_createsubscriber: creates a new logical replica from a standby server

It must be run on the target server and should be able to connect to
the source server (publisher) and the target server (subscriber).  All
tables in the specified database(s) are included in the logical
replication setup.  A pair of publication and subscription objects are
created for each database.

The main advantage of pg_createsubscriber over the common logical
replication setup is the initial data copy.  It also reduces the
catchup phase.

Some prerequisites must be met to successfully run it.  It is
basically the logical replication requirements.  It starts creating a
publication using FOR ALL TABLES and a replication slot for each
specified database.  Write recovery parameters into the target data
directory and start the target server.  It specifies the LSN of the
last replication slot (replication start point) up to which the
recovery will proceed.  Wait until the target server is promoted.
Create one subscription per specified database (using publication and
replication slot created in a previous step) on the target server.
Set the replication progress to the replication start point for each
subscription.  Enable the subscription for each specified database on
the target server.  And finally, change the system identifier on the
target server.

Author: Euler Taveira <euler.taveira@enterprisedb.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Shlok Kyal <shlok.kyal.oss@gmail.com>
Reviewed-by: Vignesh C <vignesh21@gmail.com>
Reviewed-by: Shubham Khanna <khannashubham1197@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://www.postgresql.org/message-id/flat/5ac50071-f2ed-4ace-a8fd-b892cffd33eb@www.fastmail.com

Author: petere

doc/src/sgml/ref/allfiles.sgml

@@ -205,6 +205,7 @@ Complete list of usable sgml source files in this directory.
 <!ENTITY pgCombinebackup    SYSTEM "pg_combinebackup.sgml">
 <!ENTITY pgConfig           SYSTEM "pg_config-ref.sgml">
 <!ENTITY pgControldata      SYSTEM "pg_controldata.sgml">
+<!ENTITY pgCreateSubscriber SYSTEM "pg_createsubscriber.sgml">
 <!ENTITY pgCtl              SYSTEM "pg_ctl-ref.sgml">
 <!ENTITY pgDump             SYSTEM "pg_dump.sgml">
 <!ENTITY pgDumpall          SYSTEM "pg_dumpall.sgml">