Multiple-tickets ordering scheme for transaction scheduling in multidatabase systems

Abstract

We proposed a new ticket-based global concurrency control scheme, multiple-tickets ordering scheme (MTOS). Unlike the previous schemes, MTOS employs multiple tickets at each site and uses the intrinsic conflicts using the intrinsic characteristics between global transactions. Multidatabase system (MDBS) allows users or applications to access data located in multiple local database systems (LDBSs), each of which is autonomously operated. The concurrency control problem in an MDBS is inherently difficult. Its inherent difficulties stem from the requirement that each local DBMS operate autonomously and that local transactions are permitted to execute outside of the MDBS system control. Several practical MDBS concurrency control schemes have been proposed without compromising local autonomy. However, for the purpose of ensuring the global serializability, each scheme could cause the drawbacks of global restarts, high wastage of system resources, global deadlocks, or low throughput for global/local transactions. In the previous single ticket-based scheme, the overhead incurred by the use of a single ticket for each site is considered to be severe, since global subtransactions may be either blocked or aborted at the time for them to access a ticket due to its unavailability. In contrast, using multiple tickets at each LDBS, MTOS could provide high concurrency, reduce the wastage of local resources, and prevent subtransaction abortions. In addition, MTOS uses the local order consistent with predefined global order, and then enforce conflicts that order at LDBS level. Thus, MTOS reduces the problem of ensuring global serializability in an MDBS to the problem of ensuring that the serialization order of subtransactions is consistent with the local order in a LDBS. MTOS accordingly prevents global restarts and global deadlocks. Based on the results of the performance evaluation, we conclude that MTOS outperforms the previous single ticket-based scheme.