sys.dm_os_tasks (Transact-SQL)

2023-12-19

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)

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.

Note

To call this from Azure Synapse Analytics or Analytics Platform System (PDW), use the name sys.dm_pdw_nodes_os_tasks. This syntax is not supported by serverless SQL pool in Azure Synapse Analytics.

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. DONE: Completed. 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, Analytics Platform System (PDW) The identifier for the node that this distribution is on.

Permissions

On SQL Server and SQL Managed Instance, requires VIEW SERVER STATE permission.

On SQL Database Basic, S0, and S1 service objectives, and for databases in elastic pools, the server admin account, the Microsoft Entra admin account, or membership in the ##MS_ServerStateReader## server role is required. On all other SQL Database service objectives, either the VIEW DATABASE STATE permission on the database, or membership in the ##MS_ServerStateReader## server role is required.

Permissions for SQL Server 2022 and later

Requires VIEW SERVER PERFORMANCE STATE permission on the server.

Examples

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.

Note

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

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