Chapter 9. Understanding Concurrency and Locking
In a multiuser environment, a database system must ensure that data can be accessed concurrently by the users. Access should be granted while guaranteeing integrity of the data and good performance. For example, if three different users try to update the same row of data at the same time, how should the database system behave? DB2 utilizes locking mechanisms to handle such scenarios. A DB2 user can choose different locking behaviors depending on the needs of his application—an application that requires estimated values would have a different locking behavior than one that requires precise values. Locking behaviors are controlled in DB2 by using different isolation levels. DB2 uses four isolation ...
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