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This wait type is when the background control task in SQL Server is waiting to be told to shut the instance down. There will only be one wait of this type, which will show up with a zero wait time in sys.dm_os_wait_stats, but SPID 7 will show this wait type in sys.dm_os_waiting_tasks and sys.dm_exec_requests with an increasing wait time since the instance started.

(Books Online description: “Used by the service control task while waiting for requests from the Service Control Manager. Long waits are expected and do not indicate a problem.”)

Questions/comments on this wait type? Click here to send Paul an email, especially if you have any information to add to this topic.

Added in SQL Server version:


Removed in SQL Server version:


Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 157 in 2008 and 2008 R2, and 161 in 2012 and 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

I have not seen this wait type be a noticeable point of contention.

This wait type is one that I usually filter out as a benign wait when doing wait statistics analysis.

Known occurrences in SQL Server (list number matches call stack list):

  1. Waiting for the signal to shut down SQL Server

Abbreviated call stacks (list number matches known occurrences list):

  1. SOS_Task::PostWait+9e