Distributed divergence control for epsilon serializability

Epsilon serializability (ESR) allows for more concurrency by permitting nonserializable interleavings of database operations among epsilon transactions (ETs). The authors present the design of distributed divergence control (DDC) algorithms for ESR in homogeneous and heterogeneous distributed databases. They first present a strict two-phase locking DDC algorithm (S2PLDDC) and an optimistic DDC algorithm (ODDC) for homogeneous distributed databases, where the local orderings of all the sub-ETs of a distributed ET are the same, and the total inconsistency of a distributed ET is simply the sum of that of all its sub-ETs. A superdatabase DDC algorithm is described for heterogeneous distributed databases, where the local orderings of all the sub-ETs of a distributed ET may not be the same, and the total inconsistency of a distributed ET may be greater than the sum of that of all its sub-ETs. As a result, in addition to local divergence control in each site, a global mechanism is needed to guarantee ESR