Affairs in the end is isolated or not isolated?

In a very long time before, the transaction isolation mechanisms are confined to the "back" of the word, but the underlying implementation of a series of questions about how repeatable read and phantom read, etc. to solve or foggy. This article is mainly about the non-repeatable reads at isolation level, to achieve consistency between the reading and the current reading of multiple transactions as well as details of the principles of multi-version concurrency control affairs in order to deepen the understanding of mysql isolation mechanism, of course, later also introduce problems for mysql locks, indexing mechanism and so on, and slowly come!