Figuring out which session is blocking a query on Microsoft SQL Server (query suspended)

I was recently debugging a case where a customer’s installation was hanging due to a database lock. The issue turned out to be that the database was not set to a default transaction level of READ COMMITTED SNAPSHOT, which the product expects. Regardless, while troubleshooting the issue, I stumbled upon a very useful SQL query that I needed to save somewhere, so here goes.

The following query lists which SQL session is blocked by which other session:

OBJECT_NAME(p.OBJECT_ID) BlockedObjectName,
h1.TEXT AS RequestingText,
h2.TEXT AS BlockingTest,
FROM sys.dm_tran_locks AS tl
INNER JOIN sys.databases db ON db.database_id = tl.resource_database_id
INNER JOIN sys.dm_os_waiting_tasks AS wt ON tl.lock_owner_address = wt.resource_address
INNER JOIN sys.partitions AS p ON p.hobt_id = tl.resource_associated_entity_id
INNER JOIN sys.dm_exec_connections ec1 ON ec1.session_id = tl.request_session_id
INNER JOIN sys.dm_exec_connections ec2 ON ec2.session_id = wt.blocking_session_id
CROSS APPLY sys.dm_exec_sql_text(ec1.most_recent_sql_handle) AS h1
CROSS APPLY sys.dm_exec_sql_text(ec2.most_recent_sql_handle) AS h2
ORDER BY tl.request_session_id

…and by following the tree (X blocked by Y, blocked by Z, etc..) one can see which session is responsible for the mess.

Other interesting queries:

sp_who2 Shows sessions connected to the database, how much time they’ve spent, as well as several other stats
select cmd,* from sys.sysprocesses
where blocked > 0
Shows currently blocked queries


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