Granularity of locks and degrees of consistency in a shared data base

The problem of choosing the appropriate Hranularit ~ (size) of lockable objects is introduced and the tradeoff between concurrency and overhead is discusseS. A locking protocol which allows simultaneous locking at various granularities by different transactions is presented. It is based on the introduction of additional lock modes besides the conventional share mode an5 exclusive mode. A proof is given of the equivalence of this protocol to a conventional one. Next the issue of consistency in a shared environment is analyze~. This discussion is motivated by the realization that some existing data base systems use automatic lock protocols which insure protection only from certain types of inconsistencies (for instance those arising from transaction backup), thereby automatically providing