Propagation of update sets is typically handled by the rather involved script invoked by snodb.perl -update_database. This script performs a variety of actions and checks to insure that a given update set is properly processed: updates are gathered up from all the slave nodes, checked on the master node, inserted into the official copy of the database on the master node, and finally propagated out to each slave node. This last step includes an email message sent to the local database maintainers, informing them that an update set is ready to be processed (which can be done via process_updates, see Sec. 8). The code is well documented and interested individuals are welcome to look at update_database.pl for more details.