i want to be sure that mysql does not send ALL data every time the databases synchronize
In that case, you are in luck. MySQL native replication always, only, ever sends "incremental" updates. In fact, it doesn't have a way to automatically send the whole thing. To initially configure replication, you have to manually copy a snapshot of the data from master to slave. After that, only the changes are transferred, in an ordered stream of change events referred to as the binary log, sometimes also called the "binlog."
Replication is based on the master server keeping track of all changes to its databases (updates, deletes, and so on) in its binary log. The binary log serves as a written record of all events that modify database structure or content (data) from the moment the server was started. Typically, SELECT statements are not recorded because they modify neither database structure nor content.
Each slave that connects to the master requests a copy of the binary log. That is, it pulls the data from the master, rather than the master pushing the data to the slave. The slave also executes the events from the binary log that it receives. This has the effect of repeating the original changes just as they were made on the master.