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Description:
This wait type is when a thread is waiting for access to a thread-safe data structure in Query Store.
(Books Online description: “Internal use only.”)
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Added in SQL Server version:
2014
Removed in SQL Server version:
N/A
Extended Events wait_type value:
The map_key value in sys.dm_xe_map_values is 981 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):
- Waiting for access to add a database to the QDS database list, in this case while starting up an instance
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):
- SOS_Task::PostWait+0x6f
WaitableBase::Wait+0x178
SOS_Mutex::Wait+0x75
CQDSManager::AddQDSDB+0x51e
CQDSManager::StartupDB+0x147
DBTABLE::StartupInDatabase+0x72a
DBTABLE::Startup+0x1b4e
DBMgr::StartupDB+0x7c9
DBMgr::StartDBsInParallel+0x5c0
DBMgr::ParallelDbStartupEntryPoint+0xf7
SOS_Task::Param::Execute+0x232
SOS_Scheduler::RunTask+0xa5