sys.dm_exec_query_resource_semaphores (Transact-SQL)

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

Returns the information about the current query-resource semaphore status in SQL Server. sys.dm_exec_query_resource_semaphores provides general query-execution memory status and allows you to determine whether the system can access enough memory. This view complements memory information obtained from sys.dm_os_memory_clerks to provide a complete picture of server memory status. sys.dm_exec_query_resource_semaphores returns one row for the regular resource semaphore and another row for the small-query resource semaphore. There are two requirements for a small-query semaphore:

  • The memory grant requested should be less than 5 MB

  • The query cost should be less than 3 cost units

Note

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

Column name Data type Description
resource_semaphore_id smallint Nonunique ID of the resource semaphore. 0 for the regular resource semaphore and 1 for the small-query resource semaphore.
target_memory_kb bigint Grant usage target in kilobytes.
max_target_memory_kb bigint Maximum potential target in kilobytes. NULL for the small-query resource semaphore.
total_memory_kb bigint Memory held by the resource semaphore in kilobytes. If the system is under memory pressure or if forced minimum memory is granted frequently, this value can be larger than the target_memory_kb or max_target_memory_kb values. Total memory is a sum of available and granted memory.
available_memory_kb bigint Memory available for a new grant in kilobytes.
granted_memory_kb bigint Total granted memory in kilobytes.
used_memory_kb bigint Physically used part of granted memory in kilobytes.
grantee_count int Number of active queries that have their grants satisfied.
waiter_count int Number of queries waiting for grants to be satisfied.
timeout_error_count bigint Total number of time-out errors since server startup. NULL for the small-query resource semaphore.
forced_grant_count bigint Total number of forced minimum-memory grants since server startup. NULL for the small-query resource semaphore.
pool_id int ID of the resource pool to which this resource semaphore belongs.
pdw_node_id int Applies to: Azure SQL Data Warehouse, Parallel Data Warehouse

The identifier for the node that this distribution is on.

Permissions

On SQL Server requires VIEW SERVER STATE permission on the server.

On SQL Database Premium Tiers requires the VIEW DATABASE STATE permission in the database. On SQL Database Standard and Basic Tiers requires the SQL Database admin account.

Remarks

Queries that use dynamic management views that include ORDER BY or aggregates might increase memory consumption and thus contribute to the problem they are troubleshooting.

Use sys.dm_exec_query_resource_semaphores for troubleshooting but do not include it in applications that will use future versions of SQL Server.

The Resource Governor feature enables a database administrator to distribute server resources among resource pools, up to a maximum of 64 pools. In SQL Server 2012 and higher, each pool behaves like a small independent server instance and requires 2 semaphores.

See Also

Execution Related Dynamic Management Views and Functions (Transact-SQL)
sys.dm_exec_query_memory_grants (Transact-SQL)