Design and analysis of concurrency control schemes for Heterogeneous Database Systems

Abstract

In Heterogeneous Database Systems (HDBS), concurrency control presents a new problem since serializability at the local level does not guarantee serializability at the global level. Several approaches have been proposed to solve the concurrency control problem in HDBS. However, most of the approaches either require some modification of the existing DBMS or put some restrictions on execution of the global transactions. The performance of these schemes are not studied very well. We propose a new scheme based on two phase processing of global transactions. In the first phase, the global transaction obtains all the locks for the data items to be accessed. The actual processing is performed in the second phase. Global locking is used to resolve direct conflicts between the global transactions and indirect conflicts are handled by controlling the subtransactions using static locking for all the locking sites. Subtransactions are submitted to the timestamping sites only when other subtransactions for the locking site get all necessary locks. When lock predeclaration is possible, our scheme shows superior performance compared to other schemes. Even for the cases when locks cannot be predeclared, our scheme shows better performance if the DBM S provides enough database cache space. In addition to a detailed simulation model for the concurrency control performance, we present an analytic model for our scheme.