Monitoring Locking in SQL Server

SQL Server 2005 or later has a specific dynamic management view (DMV) which provides detailed information regarding the active locks within the SQL Server instance that is, locks that have been already granted or they are waiting to be granted. The DMV is called: sys.dm_tran_locks.

The following T-SQL query uses sys.dm_tran_locks in order to return useful information:

SELECT
 resource_type, 
 resource_database_id,
 (select [name] from master.sys.databases where database_id =resource_database_id) as [DBName],
 (case resource_type when ‘OBJECT’ then  object_name(resource_associated_entity_id,resource_database_id) else NULL end) as ObjectName,
 resource_associated_entity_id,
 request_status, request_mode,request_session_id,
 resource_description
FROM sys.dm_tran_locks

A sample output of the above query would look like the one below:


An alternative way of monitoring the active locks is to use the “Activity Monitor” module in SQL Server Management Studio (SSMS) 2005 or later.
By joining the records returned by sys.dm_tran_locks and sys.dm_os_waiting_tasks DMVs you can get blocking information:
SELECT
 t1.resource_type,
 t1.resource_database_id,
 (select [name] from master.sys.databases where database_id =resource_database_id) as [DBName],
 t1.resource_associated_entity_id,
 (case resource_type when ‘OBJECT’ then  object_name(resource_associated_entity_id,resource_database_id) else NULL end) as ObjectName,
 t1.request_mode,
 t1.request_session_id,
 t2.blocking_session_id
FROM sys.dm_tran_locks as t1, sys.dm_os_waiting_tasks as t2
WHERE t1.lock_owner_address = t2.resource_address

The above two queries provide you with information on active locks and blocking cases and can help you identify incidents that might need manual intervention (i.e. in cases of a bad database design and when the database is accessed concurrently).