Distributed lock manager: Difference between revisions

Revision as of 10:32, 25 June 2006

Revision as of 12:19, 25 June 2006

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A lock value block is associated with each resource. This can be read by any process that has obtained a lock on the resource (other than a null lock) and can be updated by a process that has obtained a protected update or exclusive lock on it.

It can be used to hold any information about the resource that the application designer chooses. A typical use is to hold a ''version number'' of the resource. Each time the associated entity (e.g. a database record) is updated, the holder of the lock increments the lock value block. When another process wishes to read the resource, it obtains the appropriate lock and compares the current lock value with the value it had last time the process locked the resource. ItIf the value is the same, the process knows that the associated entity has not been updated since last time it read it, and therefore it is unnecessary to read it again. Hence, this technique can be used to implement various types of [[cache]] in a database or similar application.

===Deadlock detection===