RE: Handle infinite recursion in logical replication setup

Dear Vignesh,

Thank you for updating your patch!

> Let's consider an existing Multi master logical replication setup
> between Node1 and Node2 that is created using the following steps:
> a) Node1 - Publication publishing employee table - pub1
> b) Node2 - Subscription subscribing from publication pub1 with
> publish_local_only - sub1_pub1_node1
> c) Node2 - Publication publishing employee table - pub2
> d) Node1 - Subscription subscribing from publication pub2 with
> publish_local_only - sub2_pub2_node2
>
> To create a subscription in node3, we will be using the following steps:
> a) Node2 - Publication publishing employee table. - pub3
> b) Node3 - Subscription subscribing from publication in Node2 with
> publish_local_only - sub3_pub3_node2
>
> When we create a subscription in Node3, Node3 will connect to
> Node2(this will not be done in Node3) and check if the employee table
> is present in pg_subscription_rel, in our case Node2 will have
> employee table present in pg_subscription_rel (sub1_pub1_node1
> subscribing to employee table from pub1 in Node1). As employee table
> is being subscribed in node2 from node1, we will throw an error like
> below:
> postgres=# create subscription sub2 CONNECTION 'dbname =postgres port
> = 9999' publication pub2 with (publish_local_only=on);
> ERROR: CREATE/ALTER SUBSCRIPTION with publish_local_only and
> copy_data as true is not allowed when the publisher might have
> replicated data, table:public.t1 might have replicated data in the
> publisher
> HINT: Use CREATE/ALTER SUBSCRIPTION with copy_data = off or force

Thanks for kind explanation.
I read above and your doc in 0002, and I put some comments.

1. alter_subscription.sgml

```
- <term><literal>copy_data</literal> (<type>boolean</type>)</term>
+ <term><literal>copy_data</literal> (<type>boolean</type> | <literal>force</literal>)</term>
```

I thought that it should be written as enum. For example, huge_pages GUC parameter
can accept {on, off, try}, and it has been written as enum.

2. create_subscription.sgml

```
- <term><literal>copy_data</literal> (<type>boolean</type>)</term>
+ <term><literal>copy_data</literal> (<type>boolean</type> | <literal>force</literal>)</term>
```

Same as above.

3. create_subscription.sgml

```
+
+ <para>
+ If the publication tables were also subscribing data in the publisher
+ from other publishers, it will affect the
+ <command>CREATE SUBSCRIPTION</command> based on the value specified
+ for <literal>publish_local_only</literal> option. Refer to the
+ <xref linkend="sql-createsubscription-notes" /> for details.
+ </para>
```

I seeked docs, but the words " publication tables " have not seen.
How about "tables in the publication"?

4. create_subscription.sgml - about your example

In the first section, we should describe about 2-nodes case more detail
like Amit mentioned in [1]. I thought that Option-3 can be resolved by defining
subscriptions in both nodes with publish_local_only = true and copy_data = force.

> I was initially planning to add srreplicateddata field but I have
> changed it slightly to keep the design simple. Now we just check if
> the relation is present in pg_subscription_rel and throw an error if
> copy_data and publish_local_only option is specified. The changes for
> the same are available at [1].
>
> [1] -
> https://www.postgresql.org/message-id/CALDaNm0V%2B%3Db%3DCeZJNAAU
> O2PmSXH5QzNX3jADXb-0hGO_jVj0vA%40mail.gmail.com
> Thoughts?

Actually I doubted that the column is really needed, so it is good.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED