Microsoft® SQL Server 2008 R2 Unleashed

Optimistic Locking

With many applications, clients need to fetch the data to browse through it, make modifications to one or more rows, and then post the changes back to the database in SQL Server. These human-speed operations are slow in comparison to machine-speed operations, and the time lag between the fetch and post might be significant. (Consider a user who goes to lunch after retrieving the data.)

For these applications, you would not want to use normal locking schemes such as SERIALIZABLE or HOLDLOCK to lock the data so it can’t be changed from the time the user retrieves it to the time he or she applies any updates. This would violate one of the key rules for minimizing locking contention and deadlocks that you should not allow user ...