The objective of this research is to develop concurrency control algorithms for transactions in distributed database systems which achieve high throughput and low response time. Data replication is a mechanism that has been proposed for this purpose. Unfortunately, the requirement that transactions behave serializably forces considerable synchronization among replica sites and hence adversely impacts throughput and response time. This work will consider the tradeoff between serializability and throughput/response time by allowing bounded violations of the database's integrity constraints. Such violations occur when conflicting transactions are not synchronized. Under these circumstances a transaction is ignorant of the effects of some prior transactions, and so the results it returns and the modifications it makes to the database are based on incomplete information. Both the deviation from serializable behavior and the throughput/response time are directly related to the extent of ignorance. Concurrency control algorithms which bound the extent to which a transaction can be ignorant of conflicting transaction will bound the deviation from serializable behavior. Since violations of integrity constraints are not permissible in all applications, the research involves study of the characteristics of applications in which violations can be tolerated.
