During replication, a slave server creates several files that hold the binary log events relayed from the master to the slave, and to record information about the current status and location within the relay log. There are three file types used in the process:
The relay log consists of the events read from the binary log of the master and written by the slave I/O thread. Events in the relay log are executed on the slave as part of the SQL thread.
The master.info file contains the status and current configuration information for the slave's connectivity to the master. The file holds information on the master host name, login credentials, and coordinates indicating how far the slave has read from the master's binary log.
The relay-log.info file holds the status information about the execution point within the slave's relay log.