ASEP: A secure and flexible commit protocol for MLS distributed database systems
The classical Early Prepare commit protocol (EP), used in many commercial systems, is not suitable for use in multilevel secure distributed databases systems that employ a locking protocol for concurrency control. This is because EP requires that read locks are not released by a participant during its window of uncertainty; however, it is not possible for a locking protocol to provide this guarantee in a multilevel secure system (since the read lock of a higher-level transaction on a lower-level data object must be released whenever a lower-level transaction wants to write the same data). The only available work in the literature, namely the Secure Early Prepare protocol (SEP), overcomes this difficulty by aborting those distributed transactions that release their low-level read locks prematurely. We see this approach as being too restrictive. One of the major benefits of distributed processing is its robustness to failures, and SEP fails to take advantage of this. In this work, we propose the Advanced Secure Early Prepare commit protocol (ASEP) to solve the above problem together with a number of language primitives that can be used as system calls in distributed transactions. These primitives permit features like partial rollback and forward recovery to be incorporated within the transaction model, and allow a distributed transaction to proceed even when a participant has released its low-level read locks prematurely. This not only offers flexibility, but can also be used, if desired, by a sophisticated programmer to trade off consistency for atomicity of the distributed transaction.
security commit protocol distributed databases multilevel security database management systems transaction processing