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ACCESS_METHODS_ACCESSOR_CACHE

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Description:

This latch class is when a thread is waiting for access to the cache of column accessors for rowsets, essentially used by the Storage Engine to retrieve the columns asked for by the Query Processor. EX mode is for creating or removing a set of column accessors, SH mode is for looking for and using an existing set of column accessors.

(Books Online description: N/A)

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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 AM_ACCESSOR_CACHE map_value in sys.dm_xe_map_values.

The map_key value in sys.dm_xe_map_values is 133 in 2008 and 2008 R2, and 130 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. Creating new column accessors (in this case, as part of performing an online index rebuild)

And many other similar calls stacks.

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

  1. LatchBase::Suspend+0x16b8
    LatchBase::AcquireInternal+0x415
    AccessorCache::CreateAccessor+0x6a
    CreateAccessorCommon+0x295
    RowsetNewSS::CreateAccessor+0x6a
    CQScanRowsetNew::SetupRangePartitioningFilter+0x362
    CQScanRangeNew::Open+0x68
    CQScanNew::OpenHelper+0x41
    CQScanIndexNew::Open+0x43
    CQScanOnlineIndexNew::Open+0xe7
    CQScanNew::OpenHelper+0x41
    CQScanXProducerNew::Open+0xc8
    FnProducerOpen+0x44
    FnProducerThread+0x8c3
    SubprocEntrypoint+0xa7f
    SOS_Task::Param::Execute+0x21e
    SOS_Scheduler::RunTask+0xab