Pro SQL Server Internals by Dmitri Korotkevitch

Author:Dmitri Korotkevitch
Language: eng
Format: epub, pdf
Publisher: Apress, Berkeley, CA

3. Use the lowest transaction isolation level that provides the required data consistency. This reduces the time that shared (S) locks are held. Even if you swapped SELECT and UPDATE statements in our example, you could still have a deadlock in the REPEATABLE READ or SERIALIZABLE isolation levels. With those isolation levels, you would have shared (S) locks held until the end of the transaction, and they would block UPDATE statements. In READ COMMITTED mode, shared (S) locks are released after a row is read and UPDATE statements would not be blocked. In some cases, you can switch to optimistic isolation levels, which we will discuss in Chapter 22.

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