The cord approach to Extensible Concurrency Control

Abstract

Database management systems (DBMSs) have been increasingly used for advanced application do- mains, such as software development environments, network management, workflow management systems, computer-aided design and manufacturing, and managed healthcare. In these domains, the standard cor- rectness model of serializability is often too restrictive. We introduce the notion of a Concurrency Control Language (CCL) that allows a database application designer to specify concurrency control policies to tailor the behavior of a transaction manager. A well-crafted set of policies defines an extended transaction model. The necessary semantic information required by the CCL run-time engine is extracted from a task manager, a (logical) module by definition included in all advanced applications. This module stores task models that encode the semantic information about the transactions submitted to the DBMS. We have designed a rule- based CCL, called cord, and have implemented a run-time engine that can be hooked to a conventional transaction manager to implement the sophisticated concurrency control required by advanced database applications. We present an architecture for systems based on cord and describe how we integrated the cord engine with the Exodus Storage Manager to implement Altruistic Locking