Towards an Isolation Level Standard

This paper proposes a new set of isolation level characterizations that are portable across implementations. That is, these characterizations are applicable to locking implementations of the ANSI-SQL isolation levels as well as optimistic concurrency control schemes. The paper also provides definitions of some additional levels that are weaker than serializability. These include the multi-version isolation level known as Snapshot Isolation, which is provided as a fundamental method by Oracle, as well as a new level that provides consistent reads without serializability. We believe the isolation level characterizations offered here could form the basis of a new ANSI SQL standard, and we are investigating this possibility. Furthermore, our definitional approach is also a contribution, since it can be easily used to achieve definitions of isolation levels that are both precise and implementation-independent.