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This wait is when an SOS Task is entered into the queue for an SOS Node. The wait ends when the task either starts running or the enqueue times out.

(Books Online description: “Occurs when a task is started in a synchronous manner. Most tasks in SQL Server are started in an asynchronous manner, in which control returns to the starter immediately after the task request has been placed on the work queue.”)

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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 278 in 2008 and 2008 R2, 285 in 2012, and 292 in 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 contention point.

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

  1. Starting a CLR task, which will either start running or timeout after 5 seconds

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

  1. SOS_Task::PostWait+4d