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LCK_M_U

Short Description

Occurs when a task is waiting to acquire an Update lock.

Detailed Description​

This is an Update lock - your session is waiting to perform an update and is being blocked by another thread that holds a lock an incompatible mode.

For a lock compatibility matrix, see sys.dm_tran_locks (Transact-SQL).

How to reduce this wait​

  • In SQL Server Management Studio (SSMS) Object Explorer, right-click the top-level server object, expand Reports, expand Standard Reports, and then select Activity – All Blocking Transactions. This report shows current transactions at the head of a blocking chain. If you expand the transaction, the report will show the transactions that are blocked by the head transaction. This report will also show the Blocking SQL Statement and the Blocked SQL Statement.
  • Ensure your application uses SQL Server's locking mechanism in an efficient way and investigate why there has been a sudden change in locking.
  • Has there been a software release?
  • and lastly - examine the lock hierarchy to see if one thread is blocking your application are if it is safe do to so, kill the session. I reiterate, this is not something you should do lightly.

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