Isolation levels are a rare subject in MySQL literature. The documentation provides a terse description and focuses mainly on locking issues, but does not discuss the semantics of each isolation level. This is not only a problem that affects MySQL documentation but also the SQL standard itself.
Both the lack of documentation and the absence of a deeper description of the expected behavior in the SQL standard make isolation levels a topic that is more assumed than known by database administrators and developers. In this blog post, I aim to help you understand how the default isolation level in MySQL works and show you some surprising facts about it.
But first let’s see how isolation levels are described in the standard: “The transaction isolation level of a SQL-transaction defines the degree to which the operations on SQL-data, or schemas in that SQL-transaction are affected by the effects of and can affect operations on …[Read more]