Re: speed up a logical replica setup

I found some issues and fixed those issues with top up patches

v23-0012 and v23-0013

1.

Suppose there is a cascade physical replication node1->node2->node3.

Now if we run pg_createsubscriber with node1 as primary and node2 as

standby, pg_createsubscriber will be successful but the connection

between node2 and node3 will not be retained and log og node3 will

give error:

2024-02-20 12:32:12.340 IST [277664] FATAL:  database system

identifier differs between the primary and standby

2024-02-20 12:32:12.340 IST [277664] DETAIL:  The primary's identifier

is 7337575856950914038, the standby's identifier is

7337575783125171076.

2024-02-20 12:32:12.341 IST [277491] LOG:  waiting for WAL to become

available at 0/3000F10

To fix this I am avoiding pg_createsubscriber to run if the standby

node is primary to any other server.

Made the change in v23-0012 patch

2.

While checking 'max_replication_slots' in 'check_publisher' function,

we are not considering the temporary slot in the check:

+   if (max_repslots - cur_repslots < num_dbs)

+   {

+       pg_log_error("publisher requires %d replication slots, but

only %d remain",

+                    num_dbs, max_repslots - cur_repslots);

+       pg_log_error_hint("Consider increasing max_replication_slots

to at least %d.",

+                         cur_repslots + num_dbs);

+       return false;

+   }

Fixed this in v23-0013