is pg_log_standby_snapshot() really needed?

Hi,

I'm testing the ability to have a logical replica subscribed from a standby.

Of course, I'm doing this in a laboratory with no activity so
everything get stuck after creating the subscription (the main slot).
This is clearly because every time it will create a temp slot for copy
a table it needs the running xacts from the primary.

Now, I was solving this by executing CHECKPOINT on the primary, and
also noted that pg_switch_wal() works too. After that, I read about
pg_log_standby_snapshot().

So, I wonder if that function is really needed because as I said I
solved it with already existing functionality. Or if it is really
needed maybe it is a bug that a CHECKPOINT and pg_switch_wal() have
the same effect?

-- 
Jaime Casanova
Director de Servicios Profesionales
SYSTEMGUARDS - Consultores de PostgreSQL