Concurrency control and locking

Concurrency control and locking is the mechanism used by DBMSs for the sharing of data. Atomicity, consistency, and isolation are achieved through concurrency control and locking. See ACID properties (new window).

When many people may be reading the same data item at the same time, it is usually necessary to ensure that only one application at a time can change a data item. Locking is a way to do this. Because of locking, all changes to a particular data item will be made in the correct order in a transaction. See isolation (new window). 

The amount of data that can be locked with the single instance or groups of instances defines the granularity of the lock. The types of granularity are illustrated here are:

Additional information on this subject along with examples of multi-user considerations can be found in the Object Database Handbook (new window).

More detail for the current topic: Concurrency control and locking
	Page locking
	Cluster locking
	Class or table locking
	Object or instance locking

More on the general topic: Basic concepts for using a DBMS
	ACID properties

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ACID properties Concurrency control and locking

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