@Criss Isolation levels are used to specify semantics only. DBMS is free to implement them in different ways. Take a look at this VLDB 2012 paper about optimist

@Criss Isolation levels are used to specify semantics only. DBMS is free to implement them in different ways. Take a look at this VLDB 2012 paper about optimistic concurrent control in main memory databases, like MemSQL, which also describes implementation of isolation levels: http://arxiv.org/pdf/1201.0228v1.pdf http://arxiv.org/pdf/1201.0228v1.pdf