Modular Synchronization in Distributed, Multiversion Databases: Version Control and Concurrency Control

A version control mechanism is proposed that enhances the modularity and extensibility of multiversion concurrency control algorithms. We decouple the multiversion algorithms into two components: version control and concurrency control. This permits modular development of multiversion protocols, and simplifies the task of proving the correctness of these protocols. A set of procedures for version control is described that defines the interface to the version control component. We show that the same interface can be used by the database actions of both two-phase locking and time-stamp concurrency control protocols to access multiversion data. An interesting feature of our framework is that the execution of read-only transactions becomes completely independent of the underlying concurrency control implementation. Unlike other multiversion algorithms, read-only transactions in this scheme do not modify any version related information, and therefore, do not interfere with the execution of read-write transactions. Finally, the extension of the multiversion algorithms to a distributed environment becomes very simple.