What is a Relay Log in My SQL? Please reference the question. Solution The dictionary definition of relay is to recieve and pass on. It is similar in MySQL. When the server wants to replicate, it creates many logs that store the binary log events from master to slave. It contains the set of events that change the data or structure of the database. There are two parts to it: > Set of relay log files > Index file of all relay log files The step by step process of replication can be described as follows: The master is connected to IO Thread by reading the binary log events and these are replicated in the relay log.This way a new copy of the events is created..