16.8.3. Classifier Function
The classifier function is a T-SQL
function that is executed for each login, which allows you to write
logic to route incoming requests to the appropriate workload group. You
must create the classifier function in the master
database, and the Resource Governor can only use one classifier
function at any given time. You can, however, create multiple classifier
functions and dynamically change which function the Resource Governor
uses. You can use the following functions to help you create your
classifier function:
HOST_NAME()
APP_NAME()
SUSER_NAME()
SUSER_SNAME()
IS_SRVROLEMEMBER()
IS_MEMBER()
LOGINPROPERTY(suser_name(),'DefaultDatabase')
LOGINPROPERTY(suser_name(),'DefaultLanguage')
ORIGINAL_DB_NAME()
CONNECTIONPROPERTY(<PropertyName>)
You can also create a lookup
table to help you with your classifier function. For example, you may
want to send certain processes to a different workload group, depending
on a schedule you have defined in your lookup table. However, you need
to keep in mind that SQL Server will execute the classifier function for
each login, so it should be as efficient as possible in order to
prevent performance issues. A good thing to keep in mind is that the
dedicated administrator connection will never be classified, so you can
always log in using this connection to fix any issues you may encounter.
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The workload groups used in the
classifier function are case sensitive. If you do not use the correct
case when referencing the workload groups, the requests will be routed
to the default workload group.
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Let's create a classifier function that will route the incoming requests to the workload groups shown in Figure 16-15 by running the script in Listing 3.
Example 3. Code to Create and Enable a Classifier Function
USE master
GO
CREATE FUNCTION RG_Classifier_V1 ()
RETURNS sysname
WITH SCHEMABINDING
AS
BEGIN
DECLARE @GroupName sysname
IF (IS_MEMBER('KEN-PC\TestingGroup') = 1)
SET @GroupName = 'TestingGroup'
ELSE IF (APP_NAME() LIKE '%REPORT SERVER%')
SET @GroupName = 'ReportingGroup'
ELSE IF (SUSER_NAME() = 'BackupUser')
SET @GroupName = 'BackupGroup'
ELSE
SET @GroupName = 'default'
RETURN @GroupName
END
GO
--Assign the function to the Resource Governor and reconfigure
ALTER RESOURCE GOVERNOR WITH (CLASSIFIER_FUNCTION = dbo.RG_Classifier_V1)
GO
ALTER RESOURCE GOVERNOR RECONFIGURE
GO
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You can see the completed configuration (shown in Figure 3) by right-clicking on Resource Governor in SQL Server Management Studio and selecting Properties from the context menu.
In order to remove a classifier function from the Resource Governor, you can run the ALTER RESOURCE GOVERNOR statement and specify the new classifier name, or NULL if you want to remove all classifier functions and send all requests to the default workload group. The statement in Listing 4 will remove all classifier functions from the Resource Governor.
Example 4. Code to Remove All Classifier Functions from the Resource Governor
ALTER RESOURCE GOVERNOR WITH (CLASSIFIER_FUNCTION = NULL);
GO
ALTER RESOURCE GOVERNOR RECONFIGURE;
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