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description sys.dm_os_waiting_tasks (Transact-SQL)
title sys.dm_os_waiting_tasks (Transact-SQL) | Microsoft Docs
ms.custom
ms.date 03/13/2017
ms.prod sql
ms.prod_service database-engine, sql-database, sql-data-warehouse, pdw
ms.reviewer
ms.technology system-objects
ms.topic reference
f1_keywords
dm_os_waiting_tasks
sys.dm_os_waiting_tasks_TSQL
dm_os_waiting_tasks_TSQL
sys.dm_os_waiting_tasks
dev_langs
TSQL
helpviewer_keywords
sys.dm_os_waiting_tasks dynamic management view
ms.assetid ca5e6844-368c-42e2-b187-6e5f5afc8df3
author WilliamDAssafMSFT
ms.author wiassaf
monikerRange >=aps-pdw-2016||=azuresqldb-current||=azure-sqldw-latest||>=sql-server-2016||>=sql-server-linux-2017||=azuresqldb-mi-current

sys.dm_os_waiting_tasks (Transact-SQL)

[!INCLUDE sql-asdb-asdbmi-asa-pdw]

Returns information about the wait queue of tasks that are waiting on some resource. For more information about tasks, see the Thread and Task Architecture Guide.

Note

To call this from [!INCLUDEssSDWfull] or [!INCLUDEssPDW], use the name sys.dm_pdw_nodes_os_waiting_tasks.

Column name Data type Description
waiting_task_address varbinary(8) Address of the waiting task.
session_id smallint ID of the session associated with the task.
exec_context_id int ID of the execution context associated with the task.
wait_duration_ms bigint Total wait time for this wait type, in milliseconds. This time is inclusive of signal_wait_time.
wait_type nvarchar(60) Name of the wait type.
resource_address varbinary(8) Address of the resource for which the task is waiting.
blocking_task_address varbinary(8) Task that is currently holding this resource
blocking_session_id smallint ID of the session that is blocking the request. If this column is NULL, the request is not blocked, or the session information of the blocking session is not available (or cannot be identified).

-2 = The blocking resource is owned by an orphaned distributed transaction.

-3 = The blocking resource is owned by a deferred recovery transaction.

-4 = Session ID of the blocking latch owner could not be determined due to internal latch state transitions.
blocking_exec_context_id int ID of the execution context of the blocking task.
resource_description nvarchar(3072) Description of the resource that is being consumed. For more information, see the list below.
pdw_node_id int Applies to: [!INCLUDEssSDWfull], [!INCLUDEssPDW]

The identifier for the node that this distribution is on.

resource_description column

The resource_description column has the following possible values.

Thread-pool resource owner:

  • threadpool id=scheduler<hex-address>

Parallel query resource owner:

  • exchangeEvent id={Port|Pipe}<hex-address> WaitType=<exchange-wait-type> nodeId=<exchange-node-id>

Exchange-wait-type:

  • e_waitNone

  • e_waitPipeNewRow

  • e_waitPipeGetRow

  • e_waitSynchronizeConsumerOpen

  • e_waitPortOpen

  • e_waitPortClose

  • e_waitRange

Lock resource owner:

  • <type-specific-description> id=lock<lock-hex-address> mode=<mode> associatedObjectId=<associated-obj-id>

    <type-specific-description> can be:

    • For DATABASE: databaselock subresource=<databaselock-subresource> dbid=<db-id>

    • For FILE: filelock fileid=<file-id> subresource=<filelock-subresource> dbid=<db-id>

    • For OBJECT: objectlock lockPartition=<lock-partition-id> objid=<obj-id> subresource=<objectlock-subresource> dbid=<db-id>

    • For PAGE: pagelock fileid=<file-id> pageid=<page-id> dbid=<db-id> subresource=<pagelock-subresource>

    • For Key: keylock hobtid=<hobt-id> dbid=<db-id>

    • For EXTENT: extentlock fileid=<file-id> pageid=<page-id> dbid=<db-id>

    • For RID: ridlock fileid=<file-id> pageid=<page-id> dbid=<db-id>

    • For APPLICATION: applicationlock hash=<hash> databasePrincipalId=<role-id> dbid=<db-id>

    • For METADATA: metadatalock subresource=<metadata-subresource> classid=<metadatalock-description> dbid=<db-id>

    • For HOBT: hobtlock hobtid=<hobt-id> subresource=<hobt-subresource> dbid=<db-id>

    • For ALLOCATION_UNIT: allocunitlock hobtid=<hobt-id> subresource=<alloc-unit-subresource> dbid=<db-id>

    <mode> can be:

    Sch-S, Sch-M, S, U, X, IS, IU, IX, SIU, SIX, UIX, BU, RangeS-S, RangeS-U, RangeI-N, RangeI-S, RangeI-U, RangeI-X, RangeX-, RangeX-U, RangeX-X

External resource owner:

  • External ExternalResource=<wait-type>

Generic resource owner:

  • TransactionMutex TransactionInfo Workspace=<workspace-id>

  • Mutex

  • CLRTaskJoin

  • CLRMonitorEvent

  • CLRRWLockEvent

  • resourceWait

Latch resource owner:

  • <db-id>:<file-id>:<page-in-file>

  • <GUID>

  • <latch-class> (<latch-address>)

Permissions

On [!INCLUDEssNoVersion_md], requires VIEW SERVER STATE permission.
On SQL Database Basic, S0, and S1 service objectives, and for databases in elastic pools, the server admin account or the Azure Active Directory admin account is required. On all other SQL Database service objectives, the VIEW DATABASE STATE permission is required in the database.

Example

A. Identify tasks from blocked sessions.

SELECT * FROM sys.dm_os_waiting_tasks 
WHERE blocking_session_id IS NOT NULL;

B. View waiting tasks per connection

SELECT st.text AS [SQL Text], c.connection_id, w.session_id, 
  w.wait_duration_ms, w.wait_type, w.resource_address, 
  w.blocking_session_id, w.resource_description, c.client_net_address, c.connect_time
FROM sys.dm_os_waiting_tasks AS w
INNER JOIN sys.dm_exec_connections AS c ON w.session_id = c.session_id 
CROSS APPLY (SELECT * FROM sys.dm_exec_sql_text(c.most_recent_sql_handle)) AS st 
              WHERE w.session_id > 50 AND w.wait_duration_ms > 0
ORDER BY c.connection_id, w.session_id
GO

C. View waiting tasks for all user processes with additional information

SELECT 'Waiting_tasks' AS [Information], owt.session_id,
	owt.wait_duration_ms, owt.wait_type, owt.blocking_session_id,
	owt.resource_description, es.program_name, est.text,
	est.dbid, eqp.query_plan, er.database_id, es.cpu_time,
	es.memory_usage*8 AS memory_usage_KB
FROM sys.dm_os_waiting_tasks owt
INNER JOIN sys.dm_exec_sessions es ON owt.session_id = es.session_id
INNER JOIN sys.dm_exec_requests er ON es.session_id = er.session_id
OUTER APPLY sys.dm_exec_sql_text (er.sql_handle) est
OUTER APPLY sys.dm_exec_query_plan (er.plan_handle) eqp
WHERE es.is_user_process = 1
ORDER BY owt.session_id;
GO

See Also

SQL Server Operating System Related Dynamic Management Views (Transact-SQL)
Thread and Task Architecture Guide