Publication

Abstract : Software Transactional Memory Systems (STM) are a promising alternative for concurrency control in shared memory systems. Multiversion STM systems maintain multiple versions for each t-object. The advantage of storing multiple versions is that it facilitates successful execution of higher number of read operations than otherwise. Multi-Version permissiveness (mv-permissiveness) is a progress condition for multi-version STMs that states that a read-only transaction never aborts. Recently a STM system was proposed that maintains only a single version but is mv-permissive. This raises a natural question: how much concurrency can be achieved by multi-version STM. We show that fewer transactions are aborted in multi-version STMs than single-version systems. We also show that any STM system that is permissive w.r.t opacity must maintain at least as many versions as the number of live transactions. A direct implication of this result is that no single-version STM can be permissive w.r.t opacity.