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This wait type is when a thread is waiting for access to a critical section of code inside the memory allocator that steals memory from the buffer pool.
(Books Online description: N/A)
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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 128 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.
There have been cases where this wait type becomes prevalent if the server runs out of Virtual Address Space and the memory allocator takes a long time to allocate large chunks of memory. There was a bug in 2012 and 2014 that would cause this wait type – see KB article 3074434.
Known occurrences in SQL Server (list number matches call stack list):
- Waiting for the memory allocator mutex (in this case, while stealing memory from the buffer pool to give to a sort operation)
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):