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KILL (Transact-SQL)

  • Article

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric

Ends a user process that is based on the session ID or unit of work (UOW). If the specified session ID or UOW has much work to undo, the KILL statement can take some time to complete. The process takes longer to complete particularly when the process involves rolling back a long transaction.

KILL ends a normal connection, which internally stops the transactions that are associated with the specified session ID. At times, Microsoft Distributed Transaction Coordinator (MS DTC) might be in use. If MS DTC is in use, you can also use the statement to end orphaned and in-doubt distributed transactions.

Transact-SQL syntax conventions

Syntax

Syntax for SQL Server, Azure SQL Database, and Azure SQL Managed Instance:

KILL { session_id [ WITH STATUSONLY ] | UOW [ WITH STATUSONLY | COMMIT | ROLLBACK ] }
[ ; ]

Syntax for Azure Synapse Analytics, Analytics Platform System (PDW), and Microsoft Fabric:

KILL 'session_id'
[ ; ]

Arguments

session_id

The session ID of the process to end. session_id is a unique int that is assigned to each user connection when the connection is made. The session ID value is tied to the connection for the duration of the connection. When the connection ends, the integer value is released and can be reassigned to a new connection.

The following query can help you identify the session_id that you want to kill:

 SELECT conn.session_id, host_name, program_name,
     nt_domain, login_name, connect_time, last_request_end_time
FROM sys.dm_exec_sessions AS sess
JOIN sys.dm_exec_connections AS conn
    ON sess.session_id = conn.session_id;

UOW

Identifies the unit of work ID (UOW) of distributed transactions. UOW is a GUID that might be obtained from the request_owner_guid column of the sys.dm_tran_locks dynamic management view. UOW also can be obtained from the error log or through the MS DTC monitor. For more information about monitoring distributed transactions, see the MS DTC documentation.

Use KILL <UOW> to stop unresolved distributed transactions. These transactions aren't associated with any real session ID, but instead are associated artificially with session ID = -2. This session ID makes it easier to identify unresolved transactions by querying the session ID column in sys.dm_tran_locks, sys.dm_exec_sessions, or sys.dm_exec_requests dynamic management views.

WITH STATUSONLY

Used to generate a progress report for a specified UOW or session_id that is being rolled back because of an earlier KILL statement. KILL WITH STATUSONLY doesn't end or roll back the UOW or session ID. The command only displays the current progress of the rollback.

WITH COMMIT

Used to kill an unresolved distributed transaction with commit. Only applicable to distributed transactions, you must specify a UOW to use this option. For more information, see distributed transactions.

WITH ROLLBACK

Used to kill an unresolved distributed transaction with rollback. Only applicable to distributed transactions, you must specify a UOW to use this option. For more information, see distributed transactions.

Remarks

KILL is commonly used to end a process that is blocking other important processes with locks. KILL can also be used to stop a process that is executing a query that is using necessary system resources. System processes and processes running an extended stored procedure can't be ended.

Use KILL carefully, especially when critical processes are running. You can't kill your own process. You also shouldn't kill the following processes:

  • AWAITING COMMAND
  • CHECKPOINT SLEEP
  • LAZY WRITER
  • LOCK MONITOR
  • SIGNAL HANDLER

Use @@SPID to display the session ID value for the current session.

To obtain a report of active session ID values, query the session_id column of the sys.dm_tran_locks, sys.dm_exec_sessions, and sys.dm_exec_requests dynamic management views. You can also view the SPID column that the sp_who system stored procedure returns. If a rollback is in progress for a specific SPID, the cmd column in the sp_who result set for that SPID indicates KILLED/ROLLBACK.

When a particular connection has a lock on a database resource and blocks the progress of another connection, the session ID of the blocking connection shows up in the blocking_session_id column of sys.dm_exec_requests or the blk column returned by sp_who.

The KILL command can be used to resolve in-doubt distributed transactions. These transactions are unresolved distributed transactions that occur because of unplanned restarts of the database server or MS DTC coordinator. For more information about in-doubt transactions, see the "Two-Phase Commit" section in Use Marked Transactions to Recover Related Databases Consistently.

Use WITH STATUSONLY

KILL WITH STATUSONLY generates a report if the session ID or UOW rolls back because of a previous KILL <session ID> or KILL <UOW> statement. The progress report states the amount of rollback completed (in percent) and the estimated length of time left (in seconds). The report states it in the following form:

Spid|UOW <xxx>: Transaction rollback in progress. Estimated rollback completion: <yy>% Estimated time left: <zz> seconds

If the rollback of the session ID or UOW finishes before the KILL <session ID> WITH STATUSONLY or KILL <UOW> WITH STATUSONLY statement runs, KILL ... WITH STATUSONLY returns the following error:

"Msg 6120, Level 16, State 1, Line 1"
"Status report cannot be obtained. Rollback operation for Process ID <session ID> is not in progress."

This error also occurs if no session ID or UOW is being rolled back.

The same status report can be obtained by repeating the same KILL statement without using the WITH STATUSONLY option. However, we don't recommend repeating the option this way. If you repeat a KILL <session_id> statement, the new process might stop if the rollback finishes and the session ID is reassigned to a new task before the new KILL statement runs. Prevent the new process from stopping by specifying WITH STATUSONLY.

Permissions

SQL Server: Requires the ALTER ANY CONNECTION permission. ALTER ANY CONNECTION is included with membership in the sysadmin or processadmin fixed server roles.

SQL Database: Requires the KILL DATABASE CONNECTION permission. The server-level principal login has the KILL DATABASE CONNECTION permission.

Microsoft Fabric: Requires Admin permissions.

Azure Synapse Analytics: Requires Admin permissions.

Examples

A. Use KILL to stop a session

The following example shows how to stop session ID 53.

KILL 53;
GO

B. Use KILL session ID WITH STATUSONLY to obtain a progress report

The following example generates a status of the rollback process for the specific session ID.

KILL 54;
KILL 54 WITH STATUSONLY;
GO

Here's the result set.

spid 54: Transaction rollback in progress. Estimated rollback completion: 80% Estimated time left: 10 seconds.

C. Use KILL to stop an orphaned distributed transaction

The following example shows how to stop an orphaned distributed transaction (session ID = -2) with a UOW of D5499C66-E398-45CA-BF7E-DC9C194B48CF.

KILL 'D5499C66-E398-45CA-BF7E-DC9C194B48CF';

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