Sql server® 2012 t-sql fundamentals

Locks and Blocking

SQL Server uses locks to enforce the isolation property of transactions. The following sections provide 

details about locking and explain how to troubleshoot blocking situations that are caused by conflict-

ing lock requests.

Locks

Locks are control resources obtained by a transaction to guard data resources, preventing conflicting 

or incompatible access by other transactions. I’ll first cover the important lock modes supported by 

SQL Server and their compatibility, and then I’ll describe the lockable resource types.