Optimal granularity and degree of multiprogramming in a distributed database system

The optimal choices of granularity (size of a physical lock) and the degree of multiprogramming (maximum number of transactions allowed to run concurrently) for a single-site database system (SDBS) using a locking mechanism for concurrency control have been investigated by many researchers, but the case for a distributed database system (DDBS) has not been examined. Using a simulation model, we study the problem for a DDBS in various application and system environments. In particular, we have considered: the preclaim, and the claim-as-needed locking policies; three different granule placements; two different transaction sizes; and two different communication delays. Conclusions concerning the optimal choices of granularity and the degree of multiprogramming in different environments are then drawn to provide guidelines in achieving good performance in a DDBS.