GENERALIZED OPTIONAL LOCKING IN DISTRIBUTED SYSTEMS

We present optional locking as a method for significantly speeding up distributed locks, and we generalize it to mul-tiple lock types obeying a conflict relation. The generalized version can simulate the message passing paradigm on top of Distributed Shared Memory (DSM) with no more mes-sages than explicit message passing would need. Thus we argue that message passing can be viewed as a true spe-cial case of optional locking. As a consequence, the attrac-tiveness of DSM programming models should increase sig-nificantly due to well-recognized advantages such as sim-plicity and reduced software engineering cost; mixtures of both message passing and shared data access patterns can be treated uniformly. Measurements and simulations based on database benchmarks indicate a substantial performance improvement of optional locking over conventional locking even in presence of multiple lock types