Maintaining HDDBS consistence: The Quasi Serializability approach

In this paper, we introduce quasi serializability, a correctness criterion for concurrency control in heterogeneous distributed database systems (HDDBSs). Quasi serializability is a weaker criterion than serializability in that it only controls execution of global transactions. Quasi serializability is suited to HDDBS applications where local concurrency controllers (LCCs) maintain serializability of local executions. Quasi serializable executions maintain HDDBS
consistency if local transactions at different sites do not affect each other. We propose a concurrency control mechanism that generates quasi serializable executions only. The mechanism imposes no restriction on and requires no information about LCCs. It also provides a higher degree of concurrency than that based on serializability.