Database transaction isolation in MVCC model

Question

I have read about transaction isolation in MVCC model here and 2 questions arose.

• Does MVCC use locks? As far as I understood -- no, if so --
• What does this table mean?

Answer 1

The author of the table confused guarantees from isolation levels with the mechanism used to implement them. It is not required to implement isolation using locks.

Optimistic models like MVCC can provide the same guarantees without locks. They can even provide serializability by validating the read and write sets at commit time (this isn't implement in any RDBMS AFAIK, but SQL Server Hekaton will use this technique).