A two snapshot algorithm for concurrency control in multi-level secure databases

A concurrency control algorithm for replicated, secure, multilevel databases is presented. Multiversion and replicated databases can avoid starvation problems without introducing indirect channels by maintaining stable copies of old low-level data values for use by high-level transactions. The algorithm presented improves on two comparable techniques, a direct multiversion approach of T. F. Keefe and W. T. Tsai and the full replication scheme of S. Jajodia and B. Kogan (both in Proc. 1990 IEEE Symp. on Res. In Security & Privacy, May 1990). In the latter, each security level has a container that holds a copy of all lower-level data. It is shown that only a constant number of old copies (two, as it turns out) must be maintained. The correctness of the algorithm is argued, and it is demonstrated that the algorithm is free of indirect channels and starvation