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LCK_M_IS_ABORT_BLOCKERS

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Description:

This wait type is when a thread is running an online index operation and is blocked by other operations while waiting for the long-term Intent Shared lock. In this case, the WAIT_AT_LOW_PRIORITY option has been specified, the MAX_DURATION time has expired, and the blocking operations are being rolled back.

You can read more about the WAIT_AT_LOW_PRIORITY option here.

(Books Online description: “Occurs when a task is waiting to acquire an Intent Shared (IS) lock with Abort Blockers. (Related to the low priority wait option of ALTER TABLE and ALTER INDEX.)”)

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Added in SQL Server version:

2014

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 959 in 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 wait type be a noticeable contention point.

The duration of each wait of this type will be how long it takes for all operations that are blocking the online index operation to roll back (following immediately from an LCK_M_IS_LOW_PRIORITY wait from while the online index operation was waiting at low priority).

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

  1. Waiting for the Intent Shared lock during an online index operation and the blocking operations are rolling back (same stack as for LCK_M_IS_LOW_PRIORITY except for a different location in the MDL::LockObjectLocal function)

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

  1. SOS_Task::PostWait+0x9e
    EventInternal<SuspendQueueSLock>::Wait+0x1fb
    LockOwner::Sleep+0x485
    lck_lockInternal+0x10ed
    MDL::LockObjectLocal+0xdbe
    CMEDCacheEntryFactory::AcquireLock+0x61
    CMEDCatalogObject::GetCachedObjectById+0xe2
    CMEDCatalogObject::GetCachedObjectByName+0x81
    CMEDProxySchema::GetObjectByName+0x82
    IMetadataAccess::GetMultiNameObjectHelper+0x714
    CMEDAccess::GetMultiNameObject+0xdf
    CStmtAlterIndex::XretExecute+0x559
    CMsqlExecContext::ExecuteStmts<1,1>+0x427
    CMsqlExecContext::FExecute+0xa43
    CSQLSource::Execute+0x86c
    process_request+0xa57
    process_commands+0x4a3
    SOS_Task::Param::Execute+0x21e
    SOS_Scheduler::RunTask+0xab