MEMORY_ALLOCATION_EXT

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Description:

This wait type is when a thread is switching to preemptive mode while allocating memory. The preemptive switch is so that the code being executed does not have to check for quantum exhaustion.

(Books Online description: N/A)

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Added in SQL Server version:

2016

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 1100 in 2016 RTM. After 2016 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, but this post explains a case where it seems to be a bottleneck when using the HASHBYTES functionality that was introduced in SQL Server 2017.

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

1. Allocating memory (in this case, while running the background FILESTREAM garbage collector)
2. Allocating memory (in this case, while creating a new page to hold a blob value)
3. Allocating memory (in this case, while creating a new page as part of a page split operation)
4. Allocating memory (in this case, while pulling data from the MDW collection set table snapshots.performance_counter_value

And many more similar call stacks.

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

1. SOS_Task::PopWait+0xb4
   MemoryClerkInternal::AllocatePagesWithFailureMode+0x18c
   MemoryClerkInternal::AllocatePages+0x2b
   CMemThread<CMemObj>::PbGetNewPages+0x63
   TVarPageMgr<0>::PviNewVarPage+0x36
   TVarPageMgr<0>::PbAllocate+0x1dd
   CMemThread<CMemObj>::Alloc+0xa8
   SetFilter+0x5bd
   IndexDataSetSession::SetFilterInternal+0x6e
   RowsetNewSS::SetFilter+0x2f0
   CMEDScan::StartSearch+0x492
   CMIterObjects::StartIteration+0x2b1
   FsTombstoneTableAccessor::Open+0xe2
   FsGarbageCollector::CollectGarbageIteration+0x23a
   FsGarbageCollector::CollectGarbage+0x128
   FsGarbageCollector::ProcessFsGarbageCollectionForDB+0x381
   FsGarbageCollector::ProcessFsGarbageCollection+0x22f
   PeriodicTimerTask::ProcessTskPkt+0x79
   TaskReqPktTimer::ExecuteTask+0x69
   OnDemandTaskContext::ProcessTskPkt+0x31f
   SystemTaskEntryPoint+0x3d2
   OnDemandTaskContext::FuncEntryPoint+0x25
2. SOS_Task::PopWait+0xb4
   MemoryClerkInternal::AllocatePagesWithFailureMode+0x18c
   MemoryClerkInternal::AllocatePages+0x22
   BPool::Steal+0x52b
   BPool::NewPage+0x661
   PageRef::FormatInternal+0x83
   CompactSpaceAllocator::AllocateAndFixPage+0x4b9
   CompactSpaceAllocator::AllocateAndFixPageInternal+0xb1
   CompactSpaceAllocator::FindSpaceAndFixPage+0x144
   BlobBase::AllocDataNode+0x284
   Blob::InsertNonFull+0x2e4
   Blob::InsertWholePage+0x159
   Blob::Insert+0x236
   BlobManager::ReplaceAtWithILB+0x59b
   LockBytesSS::ReplaceAtWithILB+0x17
   CMainIlb::ReplaceAtWithILB+0x90
   CBlobHandleFactories::CopyIlbRaiseError+0x70
   CBlobHandleHelper::CopyBlobHandleIntoTempOrInlined+0x1ff
   CBlobHandleManagerCommon::PxvarPreprocessInternal+0x11b
   CValRowNoHrow::SetDataX+0x28
   CEsExec::FastMoveEval+0x160
   CQScanSortNew::PushRow+0x2e
3. SOS_Task::PopWait+0xb4
   MemoryClerkInternal::AllocatePagesWithFailureMode+0x18c
   MemoryClerkInternal::AllocatePages+0x22
   BPool::Steal+0x52b
   BPool::NewPage+0x661
   PageRef::SetupPageHeaderPreAllocation+0x65
   SetupPageHeaderPreAllocation+0x6c
   TargetExtentMgr::AllocPageFromTargetExtent+0x5e4
   AllocationReq::AllocateFromExistingExtents+0xa39
   AllocationReq::AllocatePages+0xdac
   AllocationReq::Allocate+0xf3
   AllocateHoBtDataPage+0x5e8
   IndexPageManager::AllocatePage+0x1ad
   SplitPage+0x8d8
   IndexDataSetSession::InsertSmallRecord+0x1b09
   IndexDataSetSession::InsertRowInternal+0x20dc
   DatasetSession::InsertRow+0x2de
   RowsetNewSS::InsertRow+0x26
   CBlobHandleFactoryMain::CreateNewBlobHandleInternal+0x1e7
   CBlobHandleFactoryMain::CreateNewBlobHandle+0x88
   CBlobHandleHelper::CopyBlobHandleIntoTempOrInlined+0x1d3
   CBlobHandleManagerCommon::PxvarPreprocessInternal+0x11b
4. SOS_Task::PopWait+0xba
   MemoryClerkInternal::AllocatePagesWithFailureMode+0x177
   MemoryClerkInternal::AllocatePages+0x28
   CCacheStoreWrappingPageAllocator::AllocatePages+0x32
   MemoryObjectFactory::CreateMemObjectInt+0x76
   MemoryObjectFactory::CreateMemObject+0xe2
   TCacheStore<CacheClockAlgorithm>::CreateMemoryObject+0x131
   CSQLSource::PmoCreateLargeCPMemObj+0x5d
   CSQLSource::CreateMsqlExecContext+0x42
   CSQLSource::Transform+0x81e
   CSQLSource::Execute+0x47f
   process_request+0xe52
   process_commands_internal+0x289
   process_messages+0x213
   SOS_Task::Param::Execute+0x231
   SOS_Scheduler::RunTask+0xad
   SOS_Scheduler::ProcessTasks+0x3cd