CONTEXT-SPECIFIC SYNCHRONIZATION FOR ATOMIC DATA-TYPES IN OBJECT-BASED DATABASES

Highly concurrent and reliable atomic data types are crucial for objec t-based databases. Deferred update (DU) and update-in-place (UIP) are two common recovery strategies for implementing atomic data types. The se two strategies place incomparable constraints on the conflict relat ions between concurrent operations resulting in incomparable synchroni zation protocols. Also, the conflict relations used are usually static in the sense that they depend only on the operation types, and the al gorithms do not use the context-specific information that may be avail able in the system. In this paper, a new synchronization mechanism tha t employs a hybrid scheme by using both DU and UIP is proposed. Furthe rmore, the protocol is dynamic in the sense that context-specific info rmation is also used to determine conflict relations among concurrent operations. Another extension is the use of ordered shared relationshi ps between locks to execute conflicting operations concurrently. The e xecution of operations is never delayed in the proposed protocol, howe ver, the commitment of the transactions invoking these operations may be delayed due to the restriction imposed by the ordered shared relati onships between locks. It is demonstrated that the sets of histories a ccepted by the two phase locking protocols using DU or UIP are proper subsets of the set of histories accepted by the proposed protocol.