RE: Disallow changing slot's failover option in transaction block

Dear Hou,

> Kuroda-San reported an issue off-list that:
>
> If user execute ALTER SUBSCRIPTION SET (failover) command inside a txn block
> and rollback, only the subscription option change can be rolled back, while the
> replication slot's failover change is preserved.
>
> This is because ALTER SUBSCRIPTION SET (failover) command internally
> executes
> the replication command ALTER_REPLICATION_SLOT to change the replication
> slot's
> failover property, but this replication command execution cannot be
> rollback.
>
> To fix it, I think we can prevent user from executing ALTER SUBSCRIPTION set
> (failover) inside a txn block, which is also consistent to the ALTER
> SUBSCRIPTION REFRESH/DROP SUBSCRIPTION command. Attach a small
> patch to address this.

Thanks for posting the patch, the fix is same as my expectation.
Also, should we add the restriction to the doc? I feel [1] can be updated.

[1]:https://www.postgresql.org/docs/devel/sql-altersubscription.html#SQL-ALTERSUBSCRIPTION-PARAMS-SET

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