Presents your 
SQL SERVER E-NEWSLETTER for December 3, 2002

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EXAMINE THE PITFALLS OF A NONREPEATABLE READ

The READ UNCOMMITTED transaction isolation level is great for a
read-only or reporting database where transactions are nonexistent or 
extremely limited. In addition, the READ UNCOMMITTED transaction isolation 
level canincrease performance on the client by reducing the locking overhead 
that SQL Server would have to do in a more restrictive transaction isolation
level.

However, a nonrepeatable read can occur when the transaction isolation
level is set to READ UNCOMMITTED. This is the least restrictive transaction 
isolation level, allowing you to read data that may or may not be in
the middle of a modification. It won't establish locks on the data and will
allow others to access the same data at the same time. Therefore, using
this method and making decisions based on the data may not be dependable.

The potential for data inconsistency when the transaction isolation
level is not restricted can cause inconsistent query results if modifications
are made during a transaction. The READ UNCOMMITTED transaction
isolation level should be restricted to specific situations where the 
potential for nonrepeatable reads is minimized.

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