sys.dm_os_wait_stats

Article
12/03/2008

Returns information about the waits encountered by threads that executed. You can use this aggregated view to diagnose performance issues with SQL Server and also with specific queries and batches.

Column name	Data type	Description
wait_type	nvarchar(60)	Name of the wait type.
waiting_tasks_count	bigint	Number of waits on this wait type. This counter is incremented at the start of each wait.
wait_time_ms	bigint	Total wait time for this wait type in milliseconds. This time is inclusive of signal_wait_time_ms.
max_wait_time_ms	bigint	Maximum wait time on this wait type.
signal_wait_time_ms	bigint	Difference between the time the waiting thread was signaled and when it started running.

Permissions

Requires VIEW SERVER STATE permission on the server.

Remarks

Types of Waits

Resource waits
Resource waits occur when a worker requests access to a resource that is not available because the resource is being used by some other worker or is not yet available. Examples of resource waits are locks, latches, network and disk I/O waits. Lock and latch waits are waits on synchronization objects

Queue waits
Queue waits occur when a worker is idle, waiting for work to be assigned. Queue waits are most typically seen with system background tasks such as the deadlock monitor and deleted record cleanup tasks. These tasks will wait for work requests to be placed into a work queue. Queue waits may also periodically become active even if no new packets have been put on the queue.

External waits
External waits occur when a SQL Server worker is waiting for an external event, such as an extended stored procedure call or a linked server query, to finish. When you diagnose blocking issues, remember that external waits do not always imply that the worker is idle, because the worker may actively be running some external code.

sys.dm_os_wait_stats shows the time for waits that have completed. This dynamic management view does not show current waits.

A SQL Server worker thread is not considered to be waiting if any of the following is true:

A resource becomes available.
A queue is nonempty.
An external process finishes.

Although the thread is no longer waiting, the thread does not have to start running immediately. This is because such a thread is first put on the queue of runnable workers and must wait for a quantum to run on the scheduler.

In SQL Server 2005 the wait-time counters are bigint values and, therefore, are not as prone to counter rollover as the equivalent counters in earlier versions of SQL Server.

Specific types of wait times during query execution can indicate bottlenecks or stall points within the query. Similarly, high wait times, or wait counts server wide can indicate bottlenecks or hot spots in interaction query interactions within the server instance. For example, lock waits indicate data contention by queries; page IO latch waits indicate slow IO response times; page latch update waits indicate incorrect file layout.

The contents of this dynamic management view can be reset by running the following command:

DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);
GO

This command resets all counters to 0.

Note

These statistics are not persisted across SQL Server restarts, and all data is cumulative since the last time the statistics were reset or the server was started.

The following table lists the wait types encountered by tasks.

Wait type	Description
ASYNC_DISKPOOL_LOCK	Occurs when there is an attempt to synchronize parallel threads that are performing tasks such as creating or initializing a file.
ASYNC_IO_COMPLETION	Occurs when a task is waiting for I/Os to finish.
ASYNC_NETWORK_IO	Occurs on network writes when the task is blocked behind the network. Verify that the client is processing data from the server.
BACKUP	Occurs when a task is blocked as part of backup processing.
BACKUP_CLIENTLOCK	Internal only.
BACKUP_OPERATOR	Occurs when a task is waiting for a tape mount. To view the tape status, query sys.dm_io_backup_tapes. If a mount operation is not pending, this wait type may indicate a hardware problem with the tape drive.
BACKUPBUFFER	Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data. This type is not typical, except when a task is waiting for a tape mount.
BACKUPIO	Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data. This type is not typical, except when a task is waiting for a tape mount.
BACKUPTHREAD	Occurs when a task is waiting for a backup task to finish. Wait times may be long, from several minutes to several hours. If the task that is being waited on is in an I/O process, this type does not indicate a problem.
BAD_PAGE_PROCESS	Occurs when the background suspect page logger is trying to avoid running more than every five seconds. Excessive suspect pages cause the logger to run frequently.
BROKER_CONNECTION_RECEIVE_TASK	Occurs when waiting for access to receive a message on a connection endpoint. Receive access to the endpoint is serialized.
BROKER_ENDPOINT_STATE_MUTEX	Occurs when there is contention to access the state of a Service Broker connection endpoint. Access to the state for changes is serialized.
BROKER_EVENTHANDLER	Occurs when a task is waiting in the primary event handler of the Service Broker. This should occur very briefly.
BROKER_INIT	Occurs when initializing Service Broker in each active database. This should occur infrequently.
BROKER_MASTERSTART	Occurs when a task is waiting for the primary event handler of the Service Broker to start. This should occur very briefly.
BROKER_RECEIVE_WAITFOR	Occurs when the RECEIVE WAITFOR is waiting. This is typical if no messages are ready to be received.
BROKER_REGISTERALLENDPOINTS	Occurs during the initialization of a Service Broker connection endpoint. This should occur very briefly.
BROKER_SHUTDOWN	Occurs when there is a planned shutdown of Service Broker. This should occur very briefly, if at all.
BROKER_TRANSMITTER	Occurs when the Service Broker transmitter is waiting for work.
BUILTIN_HASHKEY_MUTEX	May occur after startup of instance, while internal data structures are initializing. Will not recur once data structures have initialized.
CHECKPOINT_QUEUE	Occurs while the checkpoint task is waiting for the next checkpoint request.
CHKPT	Occurs at server startup to tell the checkpoint thread that it can start.
CLR_AUTO_EVENT	Occurs when a task is currently performing common language runtime (CLR) execution and is waiting for a particular autoevent to be initiated.
CLR_CRST	Occurs when a task is currently performing CLR execution and is waiting to enter a critical section of the task that is currently being used by another task.
CLR_JOIN	Occurs when a task is currently performing CLR execution and waiting for another task to end. This wait state occurs when there is a join between tasks.
CLR_MANUAL_EVENT	Occurs when a task is currently performing CLR execution and is waiting for a specific manual event to be initiated.
CLR_MONITOR	Occurs when a task is currently performing CLR execution and is waiting to obtain a lock on the monitor.
CLR_RWLOCK_READER	Occurs when a task is currently performing CLR execution and is waiting for a reader lock.
CLR_RWLOCK_WRITER	Occurs when a task is currently performing CLR execution and is waiting for a writer lock.
CLR_SEMAPHORE	Occurs when a task is currently performing CLR execution and is waiting for a semaphore.
CLR_TASK_START	Occurs while waiting for a CLR task to complete startup.
CMEMTHREAD	Occurs when a task is waiting on a thread-safe memory object. The wait time might increase when there is contention caused by multiple tasks trying to allocate memory from the same memory object.
CURSOR	Internal only.
CURSOR_ASYNC	Internal only.
CXPACKET	Occurs when trying to synchronize the query processor exchange iterator. You may consider lowering the degree of parallelism if contention on this wait type becomes a problem.
DBMIRROR_DBM_EVENT	Internal only.
DBMIRROR_DBM_MUTEX	Internal only.
DBMIRROR_EVENTS_QUEUE	Occurs when database mirroring waits for events to process.
DBMIRROR_SEND	Occurs when a task is waiting for a communications backlog at the network layer to clear to be able to send messages. Indicates that the communications layer is starting to become overloaded and affect the database mirroring data throughput.
DBMIRROR_WORKER_QUEUE	Indicates that the database mirroring worker task is waiting for more work.
DBMIRRORING_CMD	Occurs when a task is waiting for log records to be flushed to disk. This wait state is expected to be held for long periods of time.
DBTABLE	Internal only.
DEADLOCK_ENUM_MUTEX	Occurs when the deadlock monitor and sys.dm_os_waiting_tasks try to make sure that SQL Server is not running multiple deadlock searches at the same time.
DEADLOCK_TASK_SEARCH	Large waiting time on this resource indicates that the server is executing queries on top of sys.dm_os_waiting_tasks, and these queries are blocking deadlock monitor from running deadlock search. This wait type is used by deadlock monitor only. Queries on top of sys.dm_os_waiting_tasks use DEADLOCK_ENUM_MUTEX.
DEBUG	Occurs during Transact-SQL and CLR debugging for internal synchronization.
DISABLE_VERSIONING	Occurs when SQL Server polls the version transaction manager to see whether the timestamp of the earliest active transaction is later than the timestamp of when the state started changing. If this is this case, all the snapshot transactions that were started before the ALTER DATABASE statement was run have finished. This wait state is used when SQL Server disables versioning by using the ALTER DATABASE statement.
DISKIO_SUSPEND	Occurs when a task is waiting to access a file when an external backup is active. This is reported for each waiting user process. A count larger than five per user process may indicate that the external backup is taking too much time to finish.
DLL_LOADING_MUTEX	Occurs once while waiting for the XML parser DLL to load.
DROPTEMP	Occurs between attempts to drop a temporary object if the previous attempt failed. The wait duration grows exponentially with each failed drop attempt.
DTC	Occurs when a task is waiting on an event that is used to manage state transition. This state controls when the recovery of Microsoft Distributed Transaction Coordinator (MS DTC) transactions occurs after SQL Server receives notification that the MS DTC service has become unavailable. This state also describes a task that is waiting when a commit of a MS DTC transaction is initiated by SQL Server and SQL Server is waiting for the MS DTC commit to finish.
DTC_ABORT_REQUEST	Occurs in a MS DTC worker session when the session is waiting to take ownership of a MS DTC transaction. After MS DTC owns the transaction, the session can roll back the transaction. Generally, the session will wait for another session that is using the transaction.
DTC_RESOLVE	Occurs when a recovery task is waiting for the master database in a cross-database transaction so that the task can query the outcome of the transaction.
DTC_STATE	Occurs when a task is waiting on an event that protects changes to the internal MS DTC global state object. This state should be held for very short periods of time.
DTC_TMDOWN_REQUEST	Occurs in a MS DTC worker session when SQL Server receives notification that the MS DTC service is not available. First, the worker will wait for the MS DTC recovery process to start. Then, the worker waits to obtain the outcome of the distributed transaction that the worker is working on. This may continue until the connection with the MS DTC service has been reestablished.
DTC_WAITFOR_OUTCOME	Occurs when recovery tasks wait for MS DTC to become active to enable the resolution of prepared transactions.
DUMP_LOG_COORDINATOR	Occurs when a main task is waiting for a subtask to generate data. Ordinarily, this state does not occur. A long wait indicates an unexpected blockage. The subtask should be investigated.
EC	Internal only.
EE_PMOLOCK	Occurs during synchronization of certain types of memory allocations during statement execution.
EE_SPECPROC_MAP_INIT	Occurs during synchronization of internal procedure hash table creation. This wait can only occur during the initial accessing of the hash table after the SQL Server 2005 instance starts.
ENABLE_VERSIONING	Occurs when SQL Server waits for all update transactions in this database to finish before declaring the database ready to transition to snapshot isolation allowed state. This state is used when SQL Server enables snapshot isolation by using the ALTER DATABASE statement.
ERROR_REPORTING_MANAGER	Occurs during synchronization of multiple concurrent error log initializations.
EXCHANGE	Occurs during synchronization in the query processor exchange iterator during parallel queries.
EXECSYNC	Occurs during parallel queries while synchronizing in query processor in areas not related to the exchange iterator. Examples of such areas are bitmaps, large binary objects (LOBs), and the spool iterator. LOBs may frequently use this wait state.
FAILPOINT	Internal only.
FCB_REPLICA_READ	Occurs when the reads of a snapshot (or a temporary snapshot created by DBCC) sparse file are synchronized.
FCB_REPLICA_WRITE	Occurs when the pushing or pulling of a page to a snapshot (or a temporary snapshot created by DBCC) sparse file is synchronized.
FT_RESTART_CRAWL	Occurs when a full-text crawl needs to restart from a last known good point to recover from a transient failure. The wait lets the worker tasks currently working on that population to complete or exit the current step.
FT_RESUME_CRAWL	Internal only.
FULLTEXT GATHERER	Occurs during synchronization of full-text operations.
HTTP_ENDPOINT_COLLCREATE	Internal only.
HTTP_ENUMERATION	Occurs at startup to enumerate the HTTP endpoints to start HTTP.
HTTP_START	Occurs when a connection is waiting for HTTP to complete initialization.
IMP_IMPORT_MUTEX	Internal only.
IMPPROV_IOWAIT	Occurs when SQL Server waits for a bulkload I/O to finish.
INDEX_USAGE_STATS_MUTEX	Internal only.
IO_AUDIT_MUTEX	Occurs during synchronization of trace event buffers.
IO_COMPLETION	Occurs while waiting for I/O operations to complete. This wait type generally represents non-data page I/Os. Data page I/O completion waits appear as PAGEIOLATCH_* waits.
KSOURCE_WAKEUP	Used by the service control task while waiting for requests from the Service Control Manager. Long waits are expected and do not indicate a problem.
KTM_ENLISTMENT	Internal only.
KTM_RECOVERY_MANAGER	Internal only.
KTM_RECOVERY_RESOLUTION	Internal only.
LATCH_DT	Occurs when waiting for a DT (destroy) latch. This does not include buffer latches or transaction mark latches. A listing of LATCH_* waits is available in sys.dm_os_latch_stats. Note that sys.dm_os_latch_stats groups LATCH_NL, LATCH_SH, LATCH_UP, LATCH_EX, and LATCH_DT waits together.
LATCH_EX	Occurs when waiting for an EX (exclusive) latch. This does not include buffer latches or transaction mark latches. A listing of LATCH_* waits is available in sys.dm_os_latch_stats. Note that sys.dm_os_latch_stats groups LATCH_NL, LATCH_SH, LATCH_UP, LATCH_EX, and LATCH_DT waits together.
LATCH_KP	Occurs when waiting for a KP (keep) latch. This does not include buffer latches or transaction mark latches. A listing of LATCH_* waits is available in sys.dm_os_latch_stats. Note that sys.dm_os_latch_stats groups LATCH_NL, LATCH_SH, LATCH_UP, LATCH_EX, and LATCH_DT waits together.
LATCH_NL	Internal only.
LATCH_SH	Occurs when waiting for an SH (share) latch. This does not include buffer latches or transaction mark latches. A listing of LATCH_* waits is available in sys.dm_os_latch_stats. Note that sys.dm_os_latch_stats groups LATCH_NL, LATCH_SH, LATCH_UP, LATCH_EX, and LATCH_DT waits together.
LATCH_UP	Occurs when waiting for an UP (update) latch. This does not include buffer latches or transaction mark latches. A listing of LATCH_* waits is available in sys.dm_os_latch_stats. Note that sys.dm_os_latch_stats groups LATCH_NL, LATCH_SH, LATCH_UP, LATCH_EX, and LATCH_DT waits together.
LAZYWRITER_SLEEP	Occurs when lazywriter tasks are suspended. This is a measure of the time spent by background tasks that are waiting. Do not consider this state when you are looking for user stalls.
LCK_M_BU	Occurs when a task is waiting to acquire a Bulk Update (BU) lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_IS	Occurs when a task is waiting to acquire an Intent Shared (IS) lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_IU	Occurs when a task is waiting to acquire an Intent Update (IU) lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_IX	Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RIn_NL	Occurs when a task is waiting to acquire a NULL lock on the current key value, and an Insert Range lock between the current and previous key. A NULL lock on the key is an instant release lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RIn_S	Occurs when a task is waiting to acquire a shared lock on the current key value, and an Insert Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RIn_U	Task is waiting to acquire an Update lock on the current key value, and an Insert Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RIn_X	Occurs when a task is waiting to acquire an Exclusive lock on the current key value, and an Insert Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RS_S	Occurs when a task is waiting to acquire a Shared lock on the current key value, and a Shared Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RS_U	Occurs when a task is waiting to acquire an Update lock on the current key value, and an Update Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RX_S	Occurs when a task is waiting to acquire a Shared lock on the current key value, and an Exclusive Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RX_U	Occurs when a task is waiting to acquire an Update lock on the current key value, and an Exclusive range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_RX_X	Occurs when a task is waiting to acquire an Exclusive lock on the current key value, and an Exclusive Range lock between the current and previous key. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_S	Occurs when a task is waiting to acquire a Shared lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_SCH_M	Occurs when a task is waiting to acquire a Schema Modify lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_SCH_S	Occurs when a task is waiting to acquire a Schema Share lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_SIU	Occurs when a task is waiting to acquire a Shared With Intent Update lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_SIX	Occurs when a task is waiting to acquire a Shared With Intent Exclusive lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_U	Occurs when a task is waiting to acquire an Update lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_UIX	Occurs when a task is waiting to acquire an Update With Intent Exclusive lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LCK_M_X	Occurs when a task is waiting to acquire an Exclusive lock. For a lock compatibility matrix, see sys.dm_tran_locks.
LOGBUFFER	Occurs when a task is waiting for space in the log buffer to store a log record. Consistently high values may indicate that the log devices cannot keep up with the amount of log being generated by the server.
LOGMGR	Occurs when a task is waiting for any outstanding log I/Os to finish before shutting down the log while closing the database.
LOGMGR_FLUSH	Internal only.
LOGMGR_QUEUE	Occurs while the log writer task waits for work requests.
LOGMGR_RESERVE_APPEND	Occurs when a task is waiting to see whether log truncation frees up log space to enable the task to write a new log record. Consider increasing the size of the log file(s) for the affected database to reduce this wait.
LOWFAIL_MEMMGR_QUEUE	Occurs while waiting for memory to be available for use.
MIRROR_SEND_MESSAGE	Internal only.
MISCELLANEOUS	Internal only.
MSQL_DQ	Occurs when a task is waiting for a distributed query operation to finish. This is used to detect potential Multiple Active Result Set (MARS) application deadlocks. The wait ends when the distributed query call finishes.
MSQL_SYNC_PIPE	Internal only.
MSQL_XACT_MGR_MUTEX	Occurs when a task is waiting to obtain ownership of the session transaction manager to perform a session level transaction operation.
MSQL_XACT_MUTEX	Occurs during synchronization of transaction usage. A request must acquire the mutex before it can use the transaction.
MSQL_XP	Occurs when a task is waiting for an extended stored procedure to end. SQL Server uses this wait state to detect potential MARS application deadlocks. The wait stops when the extended stored procedure call ends.
MSSEARCH	Occurs during Full-Text Search calls. This wait ends when the full-text operation completes. It does not indicate contention, but rather the duration of full-text operations.
NET_WAITFOR_PACKET	Occurs when a connection is waiting for a network packet during a network read.
OLEDB	Occurs when SQL Server calls the Microsoft SQL Native Client OLE DB Provider. This wait type is not used for synchronization. Instead, it indicates the duration of calls to the OLE DB provider.
ONDEMAND_TASK_QUEUE	Occurs while a background task waits for high priority system task requests. Long wait times indicate that there have been no high priority requests to process, and should not cause concern.
PAGEIOLATCH_DT	Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Destroy mode. Long waits may indicate problems with the disk subsystem.
PAGEIOLATCH_EX	Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.
PAGEIOLATCH_KP	Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Keep mode. Long waits may indicate problems with the disk subsystem.
PAGEIOLATCH_NL	Internal only.
PAGEIOLATCH_SH	Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.
PAGEIOLATCH_UP	Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Update mode. Long waits may indicate problems with the disk subsystem.
PAGELATCH_DT	Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Destroy mode.
PAGELATCH_EX	Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Exclusive mode.
PAGELATCH_KP	Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Keep mode.
PAGELATCH_NL	Internal only.
PAGELATCH_SH	Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Shared mode.
PAGELATCH_UP	Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. The latch request is in Update mode.
PARALLEL_BACKUP_QUEUE	Occurs when serializing output produced by RESTORE HEADERONLY, RESTORE FILELISTONLY, or RESTORE LABELONLY.
PRINT_ROLLBACK_PROGRESS	Used to wait while user processes are ended in a database that has been transitioned by using the ALTER DATABASE termination clause. For more information, see ALTER DATABASE (Transact-SQL).
QNMANAGER_ACQUIRE	Internal only.
QPJOB_KILL	Indicates that an asynchronous automatic statistics update was canceled by a call to KILL as the update was starting to run. The terminating thread is suspended, waiting for it to start listening for KILL commands. A good value is less than one second.
QPJOB_WAITFOR_ABORT	Indicates that an asynchronous automatic statistics update was canceled by a call to KILL when it was running. The update has now completed but is suspended until the terminating thread message coordination is complete. This is an ordinary but rare state, and should be very short. A good value is less than one second.
QRY_MEM_GRANT_INFO_MUTEX	Occurs when Query Execution memory management tries to control access to static grant information list. This state lists information about the current granted and waiting memory requests. This state is a simple access control state. There should never be a long wait on this state. If this mutex is not released, all new memory-using queries will stop responding.
QUERY_EXECUTION_INDEX_SORT_EVENT_OPEN	Occurs in certain cases when offline create index build is run in parallel, and the different worker threads that are sorting synchronize access to the sort files.
QUERY_NOTIFICATION_MGR_MUTEX	Occurs during synchronization of the garbage collection queue in the Query Notification Manager.
QUERY_NOTIFICATION_SUBSCRIPTION_MUTEX	Occurs during state synchronization for transactions in Query Notifications.
QUERY_NOTIFICATION_TABLE_MGR_MUTEX	Occurs during internal synchronization within the Query Notification Manager.
QUERY_NOTIFICATION_UNITTEST_MUTEX	Internal only.
QUERY_OPTIMIZER_PRINT_MUTEX	Occurs during synchronization of query optimizer diagnostic output production. This wait type only occurs if diagnostic settings have been enabled under direction of Microsoft Product Support.
QUERY_TRACEOUT	Internal only.
RECOVER_CHANGEDB	Occurs during synchronization of database status in warm standby database.
REPL_CACHE_ACCESS	Occurs during synchronization on a replication article cache. During these waits, the replication log reader stalls, and data definition language (DDL) statements on a published table are blocked.
REPL_SCHEMA_ACCESS	Occurs during synchronization of replication schema version information. This state exists when DDL statements are executed on the replicated object, and when the log reader builds or consumes versioned schema based on DDL occurrence.
REPLICA_WRITES	Occurs while a task waits for completion of page writes to database snapshots or DBCC replicas.
REQUEST_DISPENSER_PAUSE	Occurs when a task is waiting for all outstanding I/O to complete, so that I/O to a file can be frozen for snapshot backup.
REQUEST_FOR_DEADLOCK_SEARCH	Occurs while the deadlock monitor waits to start the next deadlock search. This wait is expected between deadlock detections, and lengthy total waiting time on this resource does not indicate a problem.
RESOURCE_QUEUE	Occurs during synchronization of various internal resource queues.
RESOURCE_SEMAPHORE	Occurs when a query memory request cannot be granted immediately due to other concurrent queries. High waits and wait times may indicate excessive number of concurrent queries, or excessive memory request amounts.
RESOURCE_SEMAPHORE_MUTEX	Occurs while a query waits for its request for a thread reservation to be fulfilled. It also occurs when synchronizing query compile and memory grant requests.
RESOURCE_SEMAPHORE_QUERY_COMPILE	Occurs when the number of concurrent query compilations reaches a throttling limit. High waits and wait times may indicate excessive compilations, recompiles, or uncachable plans.
RESOURCE_SEMAPHORE_SMALL_QUERY	Occurs when memory request by a small query cannot be granted immediately due to other concurrent queries. Wait time should not exceed more than a few seconds, because the server transfers the request to the main query memory pool if it fails to grant the requested memory within a few seconds. High waits may indicate an excessive number of concurrent small queries while the main memory pool is blocked by waiting queries.
SEC_DROP_TEMP_KEY	Occurs after a failed attempt to drop a temporary security key before a retry attempt.
SERVER_IDLE_CHECK	Occurs during synchronization of SQL Server instance idle status when a resource monitor is attempting to declare a SQL Server instance as idle or trying to wake up.
SHUTDOWN	Occurs while a shutdown statement waits for active connections to exit.
SLEEP_BPOOL_FLUSH	Occurs when a checkpoint is throttling the issuance of new I/Os in order to avoid flooding the disk subsystem.
SLEEP_DBSTARTUP	Occurs during database startup while waiting for all databases to recover.
SLEEP_DCOMSTARTUP	Occurs once at most during SQL Server instance startup while waiting for DCOM initialization to complete.
SLEEP_MSDBSTARTUP	Occurs when SQL Trace waits for the msdb database to complete startup.
SLEEP_SYSTEMTASK	Occurs during the start of a background task while waiting for tempdb to complete startup.
SLEEP_TASK	Occurs when a task sleeps while waiting for a generic event to occur.
SLEEP_TEMPDBSTARTUP	Occurs while a task waits for tempdb to complete startup.
SNI_CRITICAL_SECTION	Occurs during internal synchronization within SQL Server networking components.
SNI_HTTP_ACCEPT	Internal only.
SNI_HTTP_WAITFOR_0_DISCON	Occurs during SQL Server shutdown, while waiting for outstanding HTTP connections to exit.
SOAP_READ	Occurs while waiting for an HTTP network read to complete.
SOAP_WRITE	Occurs while waiting for an HTTP network write to complete.
SOS_CALLBACK_REMOVAL	Occurs while performing synchronization on a callback list in order to remove a callback. It is not expected for this counter to change after server initialization is completed.
SOS_LOCALALLOCATORLIST	Occurs during internal synchronization in the SQL Server memory manager.
SOS_OBJECT_STORE_DESTROY_MUTEX	Occurs during internal synchronization in memory pools when destroying objects from the pool.
SOS_PROCESS_AFFINITY_MUTEX	Occurs during synchronizing of access to process affinity settings.
SOS_RESERVEDMEMBLOCKLIST	Occurs during internal synchronization in the SQL Server memory manager.
SOS_SCHEDULER_YIELD	Occurs when a task voluntarily yields the scheduler for other tasks to execute. During this wait the task is waiting for its quantum to be renewed.
SOS_STACKSTORE_INIT_MUTEX	Occurs during synchronization of internal store initialization.
SOS_SYNC_TASK_ENQUEUE_EVENT	Occurs when a task is started in a synchronous manner. Most tasks in SQL Server are started in an asynchronous manner, in which control returns to the starter immediately after the task request has been placed on the work queue.
SOS_VIRTUALMEMORY_LOW	Occurs when a memory allocation waits for a resource manager to free up virtual memory.
SOSHOST_EVENT	Occurs when a hosted component, such as CLR, waits on a SQL Server 2005 event synchronization object.
SOSHOST_INTERNAL	Occurs during synchronization of memory manager callbacks used by hosted components, such as CLR.
SOSHOST_MUTEX	Occurs when a hosted component, such as CLR, waits on a SQL Server 2005 mutex synchronization object.
SOSHOST_RWLOCK	Occurs when a hosted component, such as CLR, waits on a SQL Server 2005 reader-writer synchronization object.
SOSHOST_SEMAPHORE	Occurs when a hosted component, such as CLR, waits on a SQL Server 2005 semaphore synchronization object.
SOSHOST_SLEEP	Occurs when a hosted task sleeps while waiting for a generic event to occur. Hosted tasks are used by hosted components such as CLR.
SOSHOST_TRACELOCK	Occurs during synchronization of access to trace streams.
SOSHOST_WAITFORDONE	Occurs when a hosted component, such as CLR, waits for a task to complete.
SQLCLR_APPDOMAIN	Occurs while CLR waits for an application domain to complete startup.
SQLCLR_ASSEMBLY	Occurs while waiting for access to the loaded assembly list in the appdomain.
SQLCLR_DEADLOCK_DETECTION	Occurs while CLR waits for deadlock detection to complete.
SQLCLR_QUANTUM_PUNISHMENT	Occurs when a CLR task is throttled because it has exceeded its execution quantum. This throttling is done in order to reduce the effect of this resource-intensive task on other tasks.
SQLSORT_NORMMUTEX	Occurs during internal synchronization, while initializing internal sorting structures.
SQLSORT_SORTMUTEX	Occurs during internal synchronization, while initializing internal sorting structures.
SQLTRACE_BUFFER_FLUSH	Occurs when a task is waiting for a background task to flush trace buffers to disk every four seconds.
SQLTRACE_LOCK	Occurs during synchronization on trace buffers during a file trace.
SQLTRACE_SHUTDOWN	Occurs while trace shutdown waits for outstanding trace events to complete.
SQLTRACE_WAIT_ENTRIES	Occurs while a SQL Trace event queue waits for packets to arrive on the queue.
SRVPROC_SHUTDOWN	Occurs while the shutdown process waits for internal resources to be released to shutdown cleanly.
TEMPOBJ	Occurs when temporary object drops are synchronized. This wait is rare, and only occurs if a task has requested exclusive access for temp table drops.
THREADPOOL	Occurs when a task is waiting for a worker to run on. This can indicate that the maximum worker setting is too low, or that batch executions are taking unusually long, thus reducing the number of workers available to satisfy other batches.
TRACEWRITE	Occurs when the SQL Trace rowset trace provider waits for either a free buffer or a buffer with events to process.
TRAN_MARKLATCH_DT	Occurs when waiting for a destroy mode latch on a transaction mark latch. Transaction mark latches are used for synchronization of commits with marked transactions.
TRAN_MARKLATCH_EX	Occurs when waiting for an exclusive mode latch on a marked transaction. Transaction mark latches are used for synchronization of commits with marked transactions.
TRAN_MARKLATCH_KP	Occurs when waiting for a keep mode latch on a marked transaction. Transaction mark latches are used for synchronization of commits with marked transactions.
TRAN_MARKLATCH_NL	Internal only.
TRAN_MARKLATCH_SH	Occurs when waiting for a shared mode latch on a marked transaction. Transaction mark latches are used for synchronization of commits with marked transactions.
TRAN_MARKLATCH_UP	Occurs when waiting for an update mode latch on a marked transaction. Transaction mark latches are used for synchronization of commits with marked transactions.
TRANSACTION_MUTEX	Occurs during synchronization of access to a transaction by multiple batches.
UTIL_PAGE_ALLOC	Occurs when transaction log scans wait for memory to be available during memory pressure.
VIEW_DEFINITION_MUTEX	Occurs during synchronization on access to cached view definitions.
WAIT_FOR_RESULTS	Occurs when waiting for a query notification to be triggered.
WAITFOR	Occurs as a result of a WAITFOR Transact-SQL statement. The duration of the wait is determined by the parameters to the statement. This is a user-initiated wait.
WAITSTAT_MUTEX	Occurs during synchronization of access to the collection of statistics used to populate sys.dm_os_wait_stats.
WORKTBL_DROP	Occurs while pausing before retrying, after a failed worktable drop.
WRITELOG	Occurs while waiting for a log flush to complete. Common operations that cause log flushes are checkpoints and transaction commits.
XACT_OWN_TRANSACTION	Occurs while waiting to acquire ownership of a transaction.
XACT_RECLAIM_SESSION	Occurs while waiting for the current owner of a session to release ownership of the session.
XACTLOCKINFO	Occurs during synchronization of access to the list of locks for a transaction. In addition to the transaction itself, the list of locks is accessed by operations such as deadlock detection and lock migration during page splits.
XACTWORKSPACE_MUTEX	Occurs during synchronization of defections from a transaction, as well as the number of database locks between enlist members of a transaction.

Change History

Release	History
14 April 2006	New content: Added the following wait types: FULLTEXT GATHERER, EE_SPECPROC_MAP_INIT, ERROR_REPORTING_MANAGER. Changed content: Revised description for OLEDB wait type.
5 December 2005	New content: Added all wait types that occur in SQL Server 2005. Changed content: Updated several wait type descriptions.

14 April 2006

New content:

Added the following wait types: FULLTEXT GATHERER, EE_SPECPROC_MAP_INIT, ERROR_REPORTING_MANAGER.

Changed content:

Revised description for OLEDB wait type.

5 December 2005

New content:

Added all wait types that occur in SQL Server 2005.

Changed content:

Updated several wait type descriptions.

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