So, I can use WAL-shipping replication from Primary to the Secundary server, but it's only for full replication.
Yes.
Let's call " P " the provider/primary/master and " S " the subscriber/secundary/slave one. For partial replication (not all the tables), the solutions should use a third (intermediate / middle) server which could have both ways flow with the server P but only one way flow towards the server S. For example, a logical replication (pglogical or logical Postgresql replication) between server P and the middle server and then a WAL-shipping replication between middle server and server S. Is that right ?
That could work.
About the " FDW " solution in " an external server " (a middle one), is it possible to integrate the FDW in the P server to avoid the " external server " ?
Not sure I understand where you're going here.
=> What about the trigger-based replication systems like Slony or Londiste ; is it really necessary to have a connection or flow from the server S towards the server P ?
As far as I remember, with Slony, P must be able to connect to S, and S must be able to connect to P.
