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ACCESS_METHODS_BULK_ALLOC

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Description:

This latch class is when a thread is waiting for access to the extent cache for a bulk load or index (re)build operation, to allocate a lot of extents and put them in the extent cache.

(Books Online description: “Used to synchronize access within bulk allocators.”)

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Added in SQL Server version:

pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events latch_class value:

Maps to the BULK_EXTENT_ALLOCATOR map_value in sys.dm_xe_map_values.

The map_key value in sys.dm_xe_map_values is 13 in 2008 and 2008 R2, and 7 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:

I have not seen this latch be a noticeable contention point.

See the LATCH_EX wait type for more information about latches in general and how to troubleshoot them.

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

  1. Populating the extent cache (in this case, while allocating an extent as part of an index build)

And similar stacks around index (re)builds and bulk loads.

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

  1. XeSqlPkg::latch_suspend_end::Publish+138
    LatchBase::Suspend+16b8
    LatchBase::AcquireInternal+415
    ExtentAllocatorSingleAlloc::AllocateExtents+212
    CBulkAllocator::AllocateExtent+24d
    CBulkAllocator::AllocatePageId+bc
    CBulkAllocator::AllocateLinkedAndFormattedLeafPage+c2
    CIndBuild::AllocateNextIndexPage+15
    CIndBuild::InsertRow+c0a
    RowsetCreateIndex::InsertIndexRow+3abf
    CValRowCrtIdx::SetDataX+2c9
    CQScanIndexNew::NonOptimizedGetAndInsertRows+fa
    CQScanIndexNew::GetRow+31
    CQScanXProducerNew::GetRowHelper+53
    CQScanXProducerNew::GetRow+15
    FnProducerOpen+57
    FnProducerThread+8c3