sys.dm_os_workers (Transact-SQL)

THIS TOPIC APPLIES TO: yesSQL Server (starting with 2008)yesAzure SQL DatabaseyesAzure SQL Data Warehouse yesParallel Data Warehouse

Returns a row for every worker in the system.

Note

To call this from Azure SQL Data Warehouse or Parallel Data Warehouse, use the name sys.dm_pdw_nodes_os_workers.

Column name Data type Description
worker_address varbinary(8) Memory address of the worker.
status int Internal use only.
is_preemptive bit 1 = Worker is running with preemptive scheduling. Any worker that is running external code is run under preemptive scheduling.
is_fiber bit 1 = Worker is running with lightweight pooling. For more information, see sp_configure (Transact-SQL).
is_sick bit 1 = Worker is stuck trying to obtain a spin lock. If this bit is set, this might indicate a problem with contention on a frequently accessed object.
is_in_cc_exception bit 1 = Worker is currently handling a non- SQL Server exception.
is_fatal_exception bit Specifies whether this worker received a fatal exception.
is_inside_catch bit 1 = Worker is currently handling an exception.
is_in_polling_io_completion_routine bit 1 = Worker is currently running an I/O completion routine for a pending I/O. For more information, see sys.dm_io_pending_io_requests (Transact-SQL).
context_switch_count int Number of scheduler context switches that are performed by this worker.
pending_io_count int Number of physical I/Os that are performed by this worker.
pending_io_byte_count bigint Total number of bytes for all pending physical I/Os for this worker.
pending_io_byte_average int Average number of bytes for physical I/Os for this worker.
wait_started_ms_ticks int Point in time, in ms_ticks, when this worker entered the SUSPENDED state. Subtracting this value from ms_ticks in sys.dm_os_sys_info returns the number of milliseconds that the worker has been waiting.
wait_resumed_ms_ticks int Point in time, in ms_ticks, when this worker entered the RUNNABLE state. Subtracting this value from ms_ticks in sys.dm_os_sys_info returns the number of milliseconds that the worker has been in the runnable queue.
task_bound_ms_ticks bigint Point in time, in ms_ticks, when a task is bound to this worker.
worker_created_ms_ticks bigint Point in time, in ms_ticks, when a worker is created.
exception_num int Error number of the last exception that this worker encountered.
exception_severity int Severity of the last exception that this worker encountered.
exception_address varbinary(8) Code address that threw the exception
affinity bigint The thread affinity of the worker. Matches the affinity of the thread in sys.dm_os_threads (Transact-SQL).
state nvarchar(60) Worker state. Can be one of the following values:

INIT = Worker is currently being initialized.

RUNNING = Worker is currently running either nonpreemptively or preemptively.

RUNNABLE = The worker is ready to run on the scheduler.

SUSPENDED = The worker is currently suspended, waiting for an event to send it a signal.
start_quantum bigint Time, in milliseconds, at the start of the current run of this worker.
end_quantum bigint Time, in milliseconds, at the end of the current run of this worker.
last_wait_type nvarchar(60) Type of last wait. For a list of wait types, see sys.dm_os_wait_stats (Transact-SQL).
return_code int Return value from last wait. Can be one of the following values:

0 =SUCCESS

3 = DEADLOCK

4 = PREMATURE_WAKEUP

258 = TIMEOUT
quantum_used bigint Internal use only.
max_quantum bigint Internal use only.
boost_count int Internal use only.
tasks_processed_count int Number of tasks that this worker processed.
fiber_address varbinary(8) Memory address of the fiber with which this worker is associated.

NULL = SQL Server is not configured for lightweight pooling.
task_address varbinary(8) Memory address of the current task. For more information, see sys.dm_os_tasks (Transact-SQL).
memory_object_address varbinary(8) Memory address of the worker memory object. For more information, see sys.dm_os_memory_objects (Transact-SQL).
thread_address varbinary(8) Memory address of the thread associated with this worker. For more information, see sys.dm_os_threads (Transact-SQL).
signal_worker_address varbinary(8) Memory address of the worker that last signaled this object. For more information, see sys.dm_os_workers.
scheduler_address varbinary(8) Memory address of the scheduler. For more information, see sys.dm_os_schedulers (Transact-SQL).
processor_group smallint Stores the processor group ID that is assigned to this thread.
pdw_node_id int Applies to: Azure SQL Data Warehouse, Parallel Data Warehouse

The identifier for the node that this distribution is on.

Remarks

If the worker state is RUNNING and the worker is running nonpreemptively, the worker address matches the active_worker_address in sys.dm_os_schedulers.

When a worker that is waiting on an event is signaled, the worker is placed at the head of the runnable queue. SQL Server allows for this to happen one thousand times in a row, after which the worker is placed at the end of the queue. Moving a worker to the end of the queue has some performance implications.

Permissions

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.

Examples

You can use the following query to find out how long a worker has been running in a SUSPENDED or RUNNABLE state.

SELECT   
    t1.session_id,  
    CONVERT(varchar(10), t1.status) AS status,  
    CONVERT(varchar(15), t1.command) AS command,  
    CONVERT(varchar(10), t2.state) AS worker_state,  
    w_suspended =   
      CASE t2.wait_started_ms_ticks  
        WHEN 0 THEN 0  
        ELSE   
          t3.ms_ticks - t2.wait_started_ms_ticks  
      END,  
    w_runnable =   
      CASE t2.wait_resumed_ms_ticks  
        WHEN 0 THEN 0  
        ELSE   
          t3.ms_ticks - t2.wait_resumed_ms_ticks  
      END  
  FROM sys.dm_exec_requests AS t1  
  INNER JOIN sys.dm_os_workers AS t2  
    ON t2.task_address = t1.task_address  
  CROSS JOIN sys.dm_os_sys_info AS t3  
  WHERE t1.scheduler_id IS NOT NULL;  

Here is the result set.

 session_id status     command         worker_state w_suspended w_runnable  
 ---------- ---------- --------------- ------------ ----------- --------------------  
 4          background LAZY WRITER     SUSPENDED    688         688  
 6          background LOCK MONITOR    SUSPENDED    4657        4657
 19         background BRKR TASK       SUSPENDED    603820344   603820344  
 14         background BRKR EVENT HNDL SUSPENDED    63583641    63583641  
 51         running    SELECT          RUNNING      0           0  
 2          background RESOURCE MONITO RUNNING      0           603825954  
 3          background LAZY WRITER     SUSPENDED    422         422  
 7          background SIGNAL HANDLER  SUSPENDED    603820485   603820485  
 13         background TASK MANAGER    SUSPENDED    603824704   603824704  
 18         background BRKR TASK       SUSPENDED    603820407   603820407  
 9          background TRACE QUEUE TAS SUSPENDED    454         454  
 52         suspended  SELECT          SUSPENDED    35094       35094  
 1          background RESOURCE MONITO RUNNING      0           603825954  

In the output, when w_runnable and w_suspended are equal, this represents the time that the worker is in the SUSPENDED state. Otherwise, w_runnable represents the time that is spent by the worker in the RUNNABLE state. In the output, session 52 is SUSPENDED for 35,094 milliseconds.

See Also

SQL Server Operating System Related Dynamic Management Views (Transact-SQL)