Locking Primitives in a Database System

Locking ~s a frequently used concurrency control mechamsm m database systems. Most systems offer one or more lock modes, usually read and write modes. Here, one operatwnal lock mode is assumed for each database operation, and a criterion for "good" lock compatibdlty functions, called maximal permtssiveness, is gtven Operatmnal modes are used as a basis to define generalized update modes that correspond to arbitrary lock conversions. The notion of intention modes from System R is extended to arbnrary lock modes, and the mteractmn among the classes of lock modes thus created is studied.