An efficient multiversion algorithm for secure servicing of transaction reads

We propose an efficient multiversion algorithm for servicing read requests in secure multilevel databases. Rather than keep an arbitrary number of versions of a datum, as standard multiversion algorithms do, the algorithm presented here maintains only a small fixed number of versions—up to three—for a modified datum. Each version corresponds to the state of the datum at the end of an externally defined version period. The algorithm avoids both covert channels and starvation of high transactions, and applies to security structures that are arbitrary partial orders. The algorithm also offers long-read transactions at any security level conflict-free access to a consistent, though slightly dated, view of any authorized portion of the database. We derive constraints sufficient to guarantee one-copy serializability of executions histories, and then exhibit an algorithm that satisfies these constraints.