Locks

SQL Server uses locks to maintain data consistency in a multiuser environment. SQL Server automatically handles locking behavior, and starting with SQL Server 7.0, locking automatically escalates and de-escalates on an as-needed basis.

To help understand why locks are important, look at the banking example shown in Figure 20.1. Suppose that you decide to transfer $100 from checking to savings. Your bank decides to run a report that shows your combined balance for checking and savings. What happens if the report is run while the transfer is in progress? Would the report show a balance of $200 or $100?

Figure 20.1. How locks maintain data consistency.

The answer resides in how SQL Server uses locks to maintain data consistency. When the transaction ...

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