Efficient Global Transaction Management in Multidatabase Systems

Abstract

Concurrency control schemes for ensuring global serializability in a multidatabase system (MDBS) environment are complicated due to the autonomy of local database management systems (DBMSs). In order to develop concurrency control schemes that are simple, permit a high degree of concurrency and incur minimal overhead, we carry out a detailed study of two classes of MDBSs: trivial and semi-trivial. In a trivial MDBS, the global transaction manager (GTM) does not delay any operations and simply submits them to the local DBMSs in the order in which they arrive. In a semi-trivial MDBS, the GTM may delay the submission of commit operations belonging to global transactions, while all other operations are submitted for execution with no delay. We identify restrictions on the local DBMSs that ensure that global serializability is maintained in trivial and semi-trivial MDBSs. These restrictions are both necessary and sufficient to guarantee serializability. We also develop concurrency control schemes that preserve global serializability in semi-trivial MDBSs in the presence as well as absence of failures, and address the problem of detecting and resolving deadlocks. Our proposed schemes are simple and require only minimal information from the participating local DBMSs.