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What is Locking (Pessimistic, Optimistic)

Chapter 16
Encyclopedia of E-Collaboration
A software lock is associated with each shared object. One must acquire a lock before updating a shared object, and must release the lock once the update is completed. In pessimistic locking, a user must wait until the lock is granted explicitly before updating an object. In optimistic locking, the user can access the shared object as soon as a tentative approval is granted. If the lock request is eventually denied in optimistic locking, the object state must be restored.
Published in Chapter:
Concurrency Control in Real-Time E-Collaboration Systems
Wenbing Zhao (Cleveland State University, USA)
Copyright: © 2008 |Pages: 7
DOI: 10.4018/978-1-59904-000-4.ch015
Abstract
For all e-collaboration systems, some degree of concurrency control is needed so that two people do not step on each other’s foot. The demand for good concurrency control is especially high for the tightly coupled, real-time e-collaboration systems. Such systems require quick responses to user’s actions, and typically require a WYSIWIS (what you see is what I see) graphical user interface (Ellis, Gibbs, & Rein, 1991). This requirement, together with the fact that users are often separated geographically across wide-area networks, favors a decentralized system design where the system state is replicated at each user’s site. This places further challenges on the design of concurrency control for these systems.
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