ALTER WORKLOAD GROUP (Transact-SQL)

 

Updated: January 19, 2016

THIS TOPIC APPLIES TO:yesSQL Server (starting with 2008)noAzure SQL DatabasenoAzure SQL Data Warehouse noParallel Data Warehouse

Changes an existing Resource Governor workload group configuration, and optionally assigns it to a to a Resource Governor resource pool.

Topic link icon Transact-SQL Syntax Conventions.

  
ALTER WORKLOAD GROUP { group_name | "default" }  
[ WITH  
    ([ IMPORTANCE = { LOW | MEDIUM | HIGH } ]  
      [ [ , ] REQUEST_MAX_MEMORY_GRANT_PERCENT = value ]  
      [ [ , ] REQUEST_MAX_CPU_TIME_SEC = value ]  
      [ [ , ] REQUEST_MEMORY_GRANT_TIMEOUT_SEC = value ]   
      [ [ , ] MAX_DOP = value ]  
      [ [ , ] GROUP_MAX_REQUESTS = value ] )  
 ]  
[ USING { pool_name | "default" } ]  
[ ; ]  

group_name | "default"
Is the name of an existing user-defined workload group or the Resource Governor default workload group.

System_CAPS_ICON_note.jpg Note


Resource Governor creates the "default" and internal groups when SQL Server is installed.

The option "default" must be enclosed by quotation marks ("") or brackets ([]) when used with ALTER WORKLOAD GROUP to avoid conflict with DEFAULT, which is a system reserved word. For more information, see Database Identifiers.

System_CAPS_ICON_note.jpg Note


Predefined workload groups and resource pools all use lowercase names, such as "default". This should be taken into account for servers that use case-sensitive collation. Servers with case-insensitive collation, such as SQL_Latin1_General_CP1_CI_AS, will treat "default" and "Default" as the same.

IMPORTANCE = { LOW | MEDIUM | HIGH }
Specifies the relative importance of a request in the workload group. Importance is one of the following:

  • LOW

  • MEDIUM (default)

  • HIGH

System_CAPS_ICON_note.jpg Note


Internally each importance setting is stored as a number that is used for calculations.

IMPORTANCE is local to the resource pool; workload groups of different importance inside the same resource pool affect each other, but do not affect workload groups in another resource pool.

REQUEST_MAX_MEMORY_GRANT_PERCENT =value
Specifies the maximum amount of memory that a single request can take from the pool. This percentage is relative to the resource pool size specified by MAX_MEMORY_PERCENT.

System_CAPS_ICON_note.jpg Note


The amount specified only refers to query execution grant memory.

value must be 0 or a positive integer. The allowed range for value is from 0 through 100. The default setting for value is 25.

Note the following:

  • Setting value to 0 prevents queries with SORT and HASH JOIN operations in user-defined workload groups from running.

  • We do not recommend setting value greater than 70 because the server may be unable to set aside enough free memory if other concurrent queries are running. This may eventually lead to query time-out error 8645.

System_CAPS_ICON_note.jpg Note


If the query memory requirements exceed the limit that is specified by this parameter, the server does the following:

For user-defined workload groups, the server tries to reduce the query degree of parallelism until the memory requirement falls under the limit, or until the degree of parallelism equals 1. If the query memory requirement is still greater than the limit, error 8657 occurs.

For internal and default workload groups, the server permits the query to obtain the required memory.

Be aware that both cases are subject to time-out error 8645 if the server has insufficient physical memory.

REQUEST_MAX_CPU_TIME_SEC =value
Specifies the maximum amount of CPU time, in seconds, that a request can use. value must be 0 or a positive integer. The default setting for value is 0, which means unlimited.

System_CAPS_ICON_note.jpg Note


Resource Governor will not prevent a request from continuing if the maximum time is exceeded. However, an event will be generated. For more information, see CPU Threshold Exceeded Event Class.

REQUEST_MEMORY_GRANT_TIMEOUT_SEC =value
Specifies the maximum time, in seconds, that a query can wait for memory grant (work buffer memory) to become available.

System_CAPS_ICON_note.jpg Note


A query does not always fail when memory grant time-out is reached. A query will only fail if there are too many concurrent queries running. Otherwise, the query may only get the minimum memory grant, resulting in reduced query performance.

value must be a positive integer. The default setting for value, 0, uses an internal calculation based on query cost to determine the maximum time.

MAX_DOP =value
Specifies the maximum degree of parallelism (DOP) for parallel requests. value must be 0 or a positive integer, 1 though 255. When value is 0, the server chooses the max degree of parallelism. This is the default and recommended setting.

System_CAPS_ICON_note.jpg Note


The actual value that the Database Engine sets for MAX_DOP by might be less than the specified value. The final value is determined by the formula min(255, number of CPUs).

System_CAPS_ICON_caution.jpg Caution


Changing MAX_DOP can adversely affect a server's performance. If you must change MAX_DOP, we recommend that it be set to a value that is less than or equal to the maximum number of hardware schedulers that are present in a single NUMA node. We recommend that you do not set MAX_DOP to a value greater than 8.

MAX_DOP is handled as follows:

  • MAX_DOP as a query hint is honored as long as it does not exceed workload group MAX_DOP.

  • MAX_DOP as a query hint always overrides sp_configure 'max degree of parallelism'.

  • Workload group MAX_DOP overrides sp_configure 'max degree of parallelism'.

  • If the query is marked as serial (MAX_DOP = 1 ) at compile time, it cannot be changed back to parallel at run time regardless of the workload group or sp_configure setting.

After DOP is configured, it can only be lowered on grant memory pressure. Workload group reconfiguration is not visible while waiting in the grant memory queue.

GROUP_MAX_REQUESTS =value
Specifies the maximum number of simultaneous requests that are allowed to execute in the workload group. value must be 0 or a positive integer. The default setting for value, 0, allows unlimited requests. When the maximum concurrent requests are reached, a user in that group can log in, but is placed in a wait state until concurrent requests are dropped below the value specified.

USING { pool_name | "default" }
Associates the workload group with the user-defined resource pool identified by pool_name, which in effect puts the workload group in the resource pool. If pool_name is not provided or if the USING argument is not used, the workload group is put in the predefined Resource Governor default pool.

The option "default" must be enclosed by quotation marks ("") or brackets ([]) when used with ALTER WORKLOAD GROUP to avoid conflict with DEFAULT, which is a system reserved word. For more information, see Database Identifiers.

System_CAPS_ICON_note.jpg Note


The option "default" is case-sensitive.

ALTER WORKLOAD GROUP is allowed on the default group.

Changes to the workload group configuration do not take effect until after ALTER RESOURCE GOVERNOR RECONFIGURE is executed. When changing a plan affecting setting, the new setting will only take effect in previously cached plans after executing DBCC FREEPROCCACHE (pool_name), where pool_name is the name of a Resource Governor resource pool on which the workload group is associated with.

  • If you are changing MAX_DOP to 1, executing DBCC FREEPROCCACHE is not required because parallel plans can run in serial mode. However, it may not be as efficient as a plan compiled as a serial plan.

  • If you are changing MAX_DOP from 1 to 0 or a value greater than 1, executing DBCC FREEPROCCACHE is not required. However, serial plans cannot run in parallel, so clearing the respective cache will allow new plans to potentially be compiled using parallelism.

System_CAPS_ICON_caution.jpg Caution


Clearing cached plans from a resource pool that is associated with more than one workload group will affect all workload groups with the user-defined resource pool identified by pool_name.

When you are executing DDL statements, we recommend that you be familiar with Resource Governor states. For more information, see Resource Governor.

REQUEST_MEMORY_GRANT_PERCENT: In SQL Server 2005, index creation is allowed to use more workspace memory than initially granted for improved performance. This special handling is supported by Resource Governor in later versions, however, the initial grant and any additional memory grant are limited by resource pool and workload group settings.

Index Creation on a Partitioned Table

The memory consumed by index creation on non-aligned partitioned table is proportional to the number of partitions involved. If the total required memory exceeds the per-query limit (REQUEST_MAX_MEMORY_GRANT_PERCENT) imposed by the Resource Governor workload group setting, this index creation may fail to execute. Because the "default" workload group allows a query to exceed the per-query limit with the minimum required memory to start for SQL Server 2005 compatibility, the user may be able to run the same index creation in "default" workload group, if the "default" resource pool has enough total memory configured to run such query.

Requires CONTROL SERVER permission.

The following example shows how to change the importance of requests in the default group from MEDIUM to LOW.

ALTER WORKLOAD GROUP "default"  
WITH (IMPORTANCE = LOW);  
GO  
ALTER RESOURCE GOVERNOR RECONFIGURE;  
GO  

The following example shows how to move a workload group from the pool that it is in to the default pool.

ALTER WORKLOAD GROUP adHoc  
USING [default];  
GO  
ALTER RESOURCE GOVERNOR RECONFIGURE;  
GO  

Resource Governor
CREATE WORKLOAD GROUP (Transact-SQL)
DROP WORKLOAD GROUP (Transact-SQL)
CREATE RESOURCE POOL (Transact-SQL)
ALTER RESOURCE POOL (Transact-SQL)
DROP RESOURCE POOL (Transact-SQL)
ALTER RESOURCE GOVERNOR (Transact-SQL)

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