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This wait type is a general wait indicating that a thread is waiting for some event to occur, including background task scheduling, during hash spills to tempdb, during a buffer pool free list stall, and for some query plan exchange operators where the wait isn’t tracked by either CXPACKET or EXECSYNC waits.
(Books Online description: “Occurs when a task sleeps while waiting for a generic event to occur.”)
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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 105 in 2008 and 2008 R2, and 109 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.
Although this is generally a benign wait type that is usually filtered out of the results from sys.dm_os_wait_stats, you may see this wait type while looking at sys.dm_os_waiting_tasks output (using my script). If that’s the case, look for hash spills happening and troubleshoot those.
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):
- Waiting for an exchange event during a scan
- Waiting for an exchange event during a stream aggregate
- Waiting for a small amount of time while trying to create a new page for the version store, and the buffer pool has no available buffers
- Waiting to determine whether to put the ghost cleanup task to sleep or to carry on using the processor if it’s idle
And many other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):