CS

CS (the default isolation level) provides the best balance between concurrency and consistency in multiple-client environments.

RS

RS provides less consistency than RR but allows more concurrency.

RR

RR provides greatest consistency.

UR

UR provides maximum concurrency, if uncommitted values are allowed in the query. It is typically used if approximate results are acceptable.

See "Types and Scope of Locks in Systems" in the for more information.