Replicators can have one of two main roles, Extractor(master) or Applier(slave)
A replicator in a master role
extracts data from a source database (for example, by reading the
binary log from a MySQL server), and generates THL. As a
master the replicator also
provides the THL to other replicators over the network connection.
A slave replicator pulls THL
data from a master and then
applies that data to a target database.