I already touched on replication issues in previous chapters, showing how the problems discussed in each chapter can affect replicated environments. This chapter focuses on issues specific to replication itself. These are mostly replication failures due to errors or slowdowns, such as a slave that lags several hours behind the master.
MySQL’s replication is asynchronous. This means the master does not care whether data on the slave is consistent. Although circular multiple master replication can be set up, in a practical sense it is a chain of servers, with each of them serving as a slave and a master at the same time.