This post was written by Seppo Jaakola, CEO of Codership.
There appears to be great misunderstanding as to what MySQL transaction isolation levels Galera CLuster actually supports and how. This blog post tries to give answer to those uncertainties.
Galera Cluster provides SNAPSHOT ISOLATION between transactions running on separate cluster nodes. Transactions running on the same node are isolated by whatever was configured as the transaction isolation level in the MySQL configuration. So, if you have configured the default REPEATABLE READ isolation, transactions issued on the same node will behave under REPEATABLE READ semantics. However, for transactions issued on separate cluster nodes, the ‘first committer wins’ rule of SNAPSHOT ISOLATION is provided, and this will fix the lost update problem that generally hurts REPEATABLE READ isolation.
Therefore, it is not safe for the application to rely on SNAPSHOT …[Read more]