An Agent Based Transaction Manager for Multidatabase Systems

A multidatabase system (MDBMS) is a facility that allows users to access data located in multiple autonomous database management systems (DBMSs) at different sites. To ensure global atomicity for multidatabase transactions, a reliable global atomic commitment protocol is a possible solution. In this protocol a centralized transaction manager (TM) receives global transactions, submits subtransactions to the appropriate sites via AGENTS. An AGENT is a component of MDBS that runs on each site; AGENTS after receiving subtransactions from the transaction manager perform the transaction and send the results back to TM. We have presented a unique proof-of-concept, a JAVA application for an Agent Based Transaction Manager that preserves global atomicity. It provides a user friendly interface through which reliable atomic commitment protocol for global transaction execution in multidatabase environment can be visualized. We demonstrated with three different test case scenarios how the protocol works. This is useful in further research in this area where atomicity of transactions can be verified for protocol correctness

A comparative study of transaction management services in multidatabase heterogeneous systems

Multidatabases are being actively researched as a relatively new area in which many aspects are not yet fully understood. This area of transaction management in multidatabase systems still has many unresolved problems. The problem areas which this dissertation addresses are classification of multidatabase systems, global concurrency control, correctness criterion in a multidatabase environment, global deadlock detection, atomic commitment and crash recovery. A core group of research addressing these problems was identified and studied. The dissertation contributes to the multidatabase transaction management topic by introducing an alternative classification method for such multiple database systems; assessing existing research into transaction management schemes and based on this assessment, proposes a transaction processing model founded on the optimal properties of transaction management identified during the course of this research.ComputingM. Sc. (Computer Science

Coping with value dependency for failure recovery in multidatabase systems

Local autonomy is the main impediment to achieving failure atomicity in a multidatabase system since it allows a local database to unilaterally commit or abort a subtransaction. Compensating a committed subtransaction is in general hard to realize due to the complication arising from the propagation of the committed effects. Resubmitting an aborted subtransaction is more realistic since the problems arising from inter-subtransaction dependencies are more predictable than those from propagation of committed effects. However, if such a dependency is cyclic or if it not only involves values but also data items, then the problem becomes more complicated. In this thesis, a failure recovery scheme¹ using resubmission is proposed. The scheme is based on distinguishing the subtransactions into two different types, and employing different strategies for them. As a result, the scheme allows an aborted subtransaction to be restarted. Compared with other failure recovery schemes which also do not rely on compensation, the scheme compromises local autonomy to a lesser extent. In this thesis, different kinds of dependencies are also studied, their impact on the correctness of resubmission method discussed and solutions proposed