RE: speed up a logical replica setup

Dear Vignesh,

> Few comments regarding the documentation:
> 1) max_replication_slots information seems to be present couple of times:
>
> + <para>
> + The target instance must have
> + <link
> linkend="guc-max-replication-slots"><varname>max_replication_slots</varna
> me></link>
> + and <link
> linkend="guc-max-logical-replication-workers"><varname>max_logical_replica
> tion_workers</varname></link>
> + configured to a value greater than or equal to the number of target
> + databases.
> + </para>
>
> + <listitem>
> + <para>
> + The target instance must have
> + <link
> linkend="guc-max-replication-slots"><varname>max_replication_slots</varna
> me></link>
> + configured to a value greater than or equal to the number of target
> + databases and replication slots.
> + </para>
> + </listitem>

Fixed.

> 2) Can we add an id to prerequisites and use it instead of referring
> to r1-app-pg_createsubscriber-1:
> - <application>pg_createsubscriber</application> checks if the
> given target data
> - directory has the same system identifier than the source data directory.
> - Since it uses the recovery process as one of the steps, it starts the
> - target server as a replica from the source server. If the system
> - identifier is not the same,
> <application>pg_createsubscriber</application> will
> - terminate with an error.
> + Checks the target can be converted. In particular, things listed in
> + <link linkend="r1-app-pg_createsubscriber-1">above section</link>
> would be
> + checked. If these are not met
> <application>pg_createsubscriber</application>
> + will terminate with an error.
> </para>

Changed.

> 3) The code also checks the following:
> Verify if a PostgreSQL binary (progname) is available in the same
> directory as pg_createsubscriber.
>
> But this is not present in the pre-requisites of documentation.

I think it is quite trivial so that I did not add.

> 4) Here we mention that the target server should be stopped, but the
> same is not mentioned in prerequisites:
> + Here is an example of using
> <application>pg_createsubscriber</application>.
> + Before running the command, please make sure target server is stopped.
> +<screen>
> +<prompt>$</prompt> <userinput>pg_ctl -D /usr/local/pgsql/data
> stop</userinput>
> +</screen>
> +

Oh, it is opposite, it should NOT be stopped. Fixed.

> 5) If there is an error during any of the pg_createsubscriber
> operation like if create subscription fails, it might not be possible
> to rollback to the earlier state which had physical-standby
> replication. I felt we should document this and also add it to the
> console message like how we do in case of pg_upgrade.

Added.

New version can be available in [1]

[1]: https://www.postgresql.org/message-id/TYCPR01MB12077CD333376B53F9CAE7AC0F5562%40TYCPR01MB12077.jpnprd01.prod.outlook.com

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/