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Description:
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:
2012
Removed in SQL Server version:
N/A
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.
Other information:
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):
- SOS_Task::PostWait+90
EventInternal<SuspendQueueSLock>::Wait+2c6
SOS_RecursiveMutex::Wait+a9
TAutoMutex<SOS_RecursiveMutex,4294967295>::GetAccess+d9
SOS_MemoryTopLevelBlockAllocator::AllocateBlock+ad
SOS_MemoryBlockAllocator::GetNewActiveBlockFromParent+271
SOS_MemoryBlockAllocator::AllocateBlockInt+17f
SOS_MemoryBlockAllocator::GetNewActiveBlockFromParent+99
SOS_MemoryBlockAllocator::AllocateBlockInt+17f
SOS_MemoryBlockAllocator::GetNewActiveBlockFromParent+99
SOS_MemoryBlockAllocator::AllocateBlockInt+17f
SOS_MemoryBlockAllocator::GetNewActiveBlockFromParent+99
SOS_MemoryBlockAllocator::AllocateBlockInt+17f
SOS_MemoryBlockAllocator::AllocateBlock+31e
SOS_MemoryWorkSpace::AllocatePage+270
MemoryClerkInternal::AllocateReservedPages+83
BPool::Steal+334
PbufGetGrantedBufs+7e
soGetBuf+ac
soAllocRecBuf+3e8
RowsetSorted::InsertRow+2b97
RowsetChangeSort::InsertRow+19