Distributed management of transactions in heterogeneous distributed database systems

Abstract

In the two phase commit protocol, the coordinator decides to commit the distributed transaction if all its subtransactions are in a state called the “prepared state”. We have increased the semantics of the two phase commit protocols by replacing the prepared state by more restrictive states called the “source state” and the “serializable state”. The source state ensures that the execution of committed distributed transactions is not only atomic but also serializable. It also ensures that distributed transactions cannot interfere with other distributed transactions through local transactions, but it does not ensure a serializable view of the distributed database if local transactions are taken into account. The serializable state ensures that the execution is serializable also if local transactions are taken into account. Which of the two correctness criteria is appropriate for global concurrency control depends on the distributed applications of the system. In the proposed mechanism, each interconnected site supports the source state or the serializable state. Various methods of supporting these states are presented. Which method is appropriate for a site depends on the concurrency control method and the autonomy requirements of the site.