ACCESS_METHODS_STRING_COMPARE

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Description:

This latch class is when a thread is waiting for access to a complex string comparison function.

(Books Online description: none)

Questions/comments on this latch class? Click here to send Paul an email, especially if you have any information to add to this topic.

Added in SQL Server version:

pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events latch_class value:

Maps to the AM_STRING_COMPARE_FUNCTION map_value in sys.dm_xe_map_values.

The map_key value in sys.dm_xe_map_values is 132 in 2008 and 2008 R2, and 129 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. Searching through an index for rows matching a search argument (in this case, while creating queue monitors for Service Broker queues that are enabled for internal activation)

And many more similar stacks ending in strings are being compared in the Access Methods code.

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

1. XeSqlPkg::latch_suspend_end::Publish+138
   LatchBase::Suspend+16b8
   LatchBase::AcquireInternal+415
   HoBtColumnAttribute::SetupComparisonFunction+6f
   EvaluateFilterArgs+1680
   IndexDataSetSession::GetNextRowValuesInternal+1730
   RowsetNewSS::GetNextRows+b7
   CMEDScan::FGetRow+9b
   CMIterObjects::GetNext+74
   CSbActivationMgr::CreateQueueMonitors+19e
   CActiveServiceBroker::BackgroundNotify+244
   CActiveServiceBrokerMgr::ASBInitializer+19b
   CActiveServiceBrokerMgr::CSbASBInitializer::IdempotentInvoke+26
   CSbTaskManager::HandleReusableTask+2b8
   CSbTask::TaskStart+14b
   CSbTask::BeginTaskStart+17
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+ab