Replication Technologies Figure 18.1 MySQL Asynchronous Replication There is also semisynchronous replication, which adds one synchronization step to the protocol. This means that the primary waits, at apply time, for the secondary to acknowledge that it has  received  the transaction. Only then does the primary resume the commit operation. Figure 18.2 MySQL Semisynchronous Replication In the two pictures there is a diagram of the classic asynchronous MySQL Replication protocol (and its semisynchronous variant as well). The arrows between the different instances represent messages exchanged between servers or messages exchanged between servers and the client application. Group Replication is a technique that can be used to implement fault-tolerant systems. The replication group is a set of servers that each have their own entire copy of the data (a shared-nothing replication 3690 18.1.1.2 Group Replication