Returns one row for each task that is active in the instance of SQL Server. A task is the basic unit of execution in SQL Server. Examples of tasks include a query, a login, a logout, and system tasks like ghost cleanup activity, checkpoint activity, log writer, parallel redo activity. For more information about tasks, see the Thread and Task Architecture Guide.
To call this from Azure Synapse Analytics (SQL Data Warehouse) or Parallel Data Warehouse, use the name sys.dm_pdw_nodes_os_tasks.
|Column name||Data type||Description|
|task_address||varbinary(8)||Memory address of the object.|
|task_state||nvarchar(60)||State of the task. This can be one of the following:
PENDING: Waiting for a worker thread.
RUNNABLE: Runnable, but waiting to receive a quantum.
RUNNING: Currently running on the scheduler.
SUSPENDED: Has a worker, but is waiting for an event.
SPINLOOP: Stuck in a spinlock.
|context_switches_count||int||Number of scheduler context switches that this task has completed.|
|pending_io_count||int||Number of physical I/Os that are performed by this task.|
|pending_io_byte_count||bigint||Total byte count of I/Os that are performed by this task.|
|pending_io_byte_average||int||Average byte count of I/Os that are performed by this task.|
|scheduler_id||int||ID of the parent scheduler. This is a handle to the scheduler information for this task. For more information, see sys.dm_os_schedulers (Transact-SQL).|
|session_id||smallint||ID of the session that is associated with the task.|
|exec_context_id||int||Execution context ID that is associated with the task.|
|request_id||int||ID of the request of the task. For more information, see sys.dm_exec_requests (Transact-SQL).|
|worker_address||varbinary(8)||Memory address of the worker that is running the task.
NULL = Task is either waiting for a worker to be able to run, or the task has just finished running.
For more information, see sys.dm_os_workers (Transact-SQL).
|host_address||varbinary(8)||Memory address of the host.
0 = Hosting was not used to create the task. This helps identify the host that was used to create this task.
For more information, see sys.dm_os_hosts (Transact-SQL).
|parent_task_address||varbinary(8)||Memory address of the task that is the parent of the object.|
|pdw_node_id||int||Applies to: Azure Synapse Analytics (SQL Data Warehouse), Parallel Data Warehouse
The identifier for the node that this distribution is on.
On SQL Server, requires
VIEW SERVER STATE permission.
On SQL Database Premium Tiers, requires the
VIEW DATABASE STATE permission in the database. On SQL Database Standard and Basic Tiers, requires the Server admin or an Azure Active Directory admin account.
A. Monitoring parallel requests
For requests that are executed in parallel, you will see multiple rows for the same combination of (<session_id>, <request_id>). Use the following query to find the Configure the max degree of parallelism Server Configuration Option for all active requests.
A request_id is unique within a session.
SELECT task_address, task_state, context_switches_count, pending_io_count, pending_io_byte_count, pending_io_byte_average, scheduler_id, session_id, exec_context_id, request_id, worker_address, host_address FROM sys.dm_os_tasks ORDER BY session_id, request_id;
B. Associating session IDs with Windows threads
You can use the following query to associate a session ID value with a Windows thread ID. You can then monitor the performance of the thread in the Windows Performance Monitor. The following query does not return information for sessions that are sleeping.
SELECT STasks.session_id, SThreads.os_thread_id FROM sys.dm_os_tasks AS STasks INNER JOIN sys.dm_os_threads AS SThreads ON STasks.worker_address = SThreads.worker_address WHERE STasks.session_id IS NOT NULL ORDER BY STasks.session_id; GO