Single-site and distributed optimistic protocols for concurrency control

The authors consider that, in spite of their advantage in removing the overhead of lock maintenance and deadlock handling, optimistic concurrency control methods have been applied less in practice than locking schemes. Two complementary approaches are introduced that may help render the optimistic approach practically viable. For the high-level approach, integration schemes can be utilized so that the database management system is provided with a variety of synchronization methods each of which can be applied to the appropriate class of transactions. The low-level approach seeks to increase the concurrency of the original optimistic method and improve its performance. The author examines the low-level approach in depth, and presents algorithms that aim at reducing back-ups and improve throughput. Both the single-site and distributed networks are considered. Optimistic schemes using time-stamps for fully duplicated and partially duplicated database networks are presented, with emphasis on performance enhancement and on reducing the overall cost of implementation