A publication can be defined on any physical replication primary. The node where a publication is defined is referred to as publisher. A publication is a set of changes generated from a table or a group of tables, and might also be described as a change set or replication set. Each publication exists in only one database.
   Publications are different from schemas and do not affect how the table is
   accessed.  Each table can be added to multiple publications if needed.
   Publications may currently only contain tables and all tables in schema.
   Objects must be added explicitly, except when a publication is created for
   ALL TABLES.
  
   Publications can choose to limit the changes they produce to
   any combination of INSERT, UPDATE,
   DELETE, and TRUNCATE, similar to how triggers are fired by
   particular event types. By default, all operation types are replicated.
   These publication specifications apply only for DML operations; they do not affect the initial
   data synchronization copy. (Row filters have no effect for
   TRUNCATE. See Section 29.4).
  
   A published table must have a replica identity configured in
   order to be able to replicate UPDATE
   and DELETE operations, so that appropriate rows to
   update or delete can be identified on the subscriber side.  By default,
   this is the primary key, if there is one.  Another unique index (with
   certain additional requirements) can also be set to be the replica
   identity.  If the table does not have any suitable key, then it can be set
   to replica identity FULL, which means the entire row becomes
   the key.  When replica identity FULL is specified,
   indexes can be used on the subscriber side for searching the rows.  Candidate
   indexes must be btree or hash, non-partial, and the leftmost index field must
   be a column (not an expression) that references the published table column.
   These restrictions on the non-unique index properties adhere to some of the
   restrictions that are enforced for primary keys.  If there are no such
   suitable indexes, the search on the subscriber side can be very inefficient,
   therefore replica identity FULL should only be used as a
   fallback if no other solution is possible.  If a replica identity other
   than FULL is set on the publisher side, a replica identity
   comprising the same or fewer columns must also be set on the subscriber
   side.  See REPLICA IDENTITY for details on
   how to set the replica identity.  If a table without a replica identity is
   added to a publication that replicates UPDATE
   or DELETE operations then
   subsequent UPDATE or DELETE
   operations will cause an error on the publisher.  INSERT
   operations can proceed regardless of any replica identity.
  
Every publication can have multiple subscribers.
   A publication is created using the CREATE PUBLICATION
   command and may later be altered or dropped using corresponding commands.
  
   The individual tables can be added and removed dynamically using
   ALTER PUBLICATION.  Both the ADD
   TABLE and DROP TABLE operations are
   transactional; so the table will start or stop replicating at the correct
   snapshot once the transaction has committed.