Concurrency Control and Recovery in Transactional

The uniied theory of concurrency control and recovery integrates atomicity and isolation within a common framework, thereby avoiding many of the shortcomings resulting from treating them as orthogonal problems. This theory can be applied to the traditional read/write model as well as to semantically rich operations. In this paper, we extend the uniied theory by applying it to generalized process structures , i.e., arbitrary partially ordered sequences of transaction invocations. Using the extended uniied theory, our goal is to provide a more exible handling of concurrent processes while allowing as much parallelism as possible. Unlike in the original uniied theory, we take into account that not all activities of a process might be compensatable and the fact that these process structures require transactional properties more general than in traditional ACID transactions. We provide a correctness criterion for transactional processes and identify the key points in which the more ex-ible structure of transactional processes implies diierences from traditional transactions. 1 Introduction In conventional databases, concurrency control and recovery are well understood problems. Unfortunately, this is not the case when transactions are grouped into entities with higher level semantics, such as transactional processes Alo97]. Some initial work has been done in this direction: studying atomicity (spheres of joint compensation Ley95], or exible transactions ELLR90, ZNBB94]) in a single process and analyzing concurrency control without considering recovery AAHD97]. Practical experience, however, shows that concurrency control and recovery are related problems and they both need to be solved in order to produce complete , feasible solutions. In this paper, we present a rst attempt to develop a theoretical framework in which to reason about concurrency