Microsoft SQL Server 2008 R2 Unleashed- P157 pdf

resource pool, this setting determines whether requests within one workload group run at a higher or lower priority than other workload groups within the same resource pool.. Memory Gran

resource pool, this setting determines whether requests within one workload group

run at a higher or lower priority than other workload groups within the same

resource pool MEDIUMis the default setting Currently, the weighting factors for each

setting is LOW=1,MEDIUM=3, and HIGH=9 This means that the scheduler will attempt to

execute sessions in workgroups with importance of HIGHthree times more often than

workgroups with MEDIUMimportance, and nine times more often workgroups with

LOWimportance

NOTE

Try to avoid having too many sessions in groups with high importance or assigning high

importance to too many groups because the sessions will likely end up getting only

equal time on the scheduler as your medium and low priority sessions

Maximum Requests—Specifies the maximum number of simultaneous requests

allowed to execute in the workload group The default setting, 0, allows unlimited

requests

CPU Time—Specifies the maximum amount of CPU time, in seconds, that a request

within the workload group can use The default setting is 0, which means unlimited

Memory Grant %—Specifies, as a percentage, the maximum amount of execution

grant memory that a single request can take from the resource pool This percentage

is relative to the amount of memory allocated to the resource pool The allowed

range of values is from 0through100 The default setting is 25 Execution grant

memory is the amount of memory used for query execution, not for data buffers or

cached plans, which can be shared by many sessions, regardless of resource pool or

workload group Note that setting this value to 0prevents queries with SORTand

HASH JOINoperations in user-defined workload groups from running It is also not

recommended that this value be set greater than 70because the server may be

unable to set aside enough free memory if other concurrent queries are running

Grant Time-out—Specifies the maximum time, in seconds, that a query waits for a

resource to become available If the resource does not become available, the process

may fail with a time-out error Note that a query does not always fail when the grant

time-out is reached A query fails only if there are too many concurrent queries

running Otherwise, the query may run with reduced resources, resulting in reduced

query performance The default setting is 0, which means the server calculates the

time-out using an internal calculation based on query cost to determine the

maximum time

Degree of Parallelism—Specifies the maximum degree of parallelism (DOP) for

parallel queries This values takes precedence over the global max degree of

paral-lelism configuration setting, as well as any query hints The allowed range of values

is from 0through64 The default setting is 0, which means that processes use the

global setting Be aware that MAX_DOPspecifies an upper limit only The actual degree

of parallelism is determined by the server based on the actual number of schedulers

and available number of parallel threads, which may be less than the specified

MAX_DOP To better understand how the MAX_DOPsetting is handled, consider the

following:

MAX_DOPas a query hint is considered only if it does not exceed the workload

groupMAX_DOPsetting

MAX_DOPas a query hint always overrides the max degree of parallelism server

configuration option

Workload group MAX_DOPalways overrides the max degree of parallelism server

configuration option

If a query is marked as serial at compile time, it cannot be changed back to

paral-lel at runtime regardless of the workload group or server configuration setting

When the degree of parallelism is decided, it can be lowered only when

memory pressure occurs Workload group reconfiguration is not seen for tasks

already waiting in the grant memory queue

To verify that the new workload group was created, in SSMS Object Explorer, expand the

Resource Governornode, expand the Resource Poolsfolder, expand the ReportPool

node, and finally, expand the Workload Groupsfolder You should then see a folder

namedReportWG1

Creating Workload Groups in T-SQL

Now that you’ve set up the ReportWG1workload group in SSMS, you are able to set up a

second workload group, OLTPWG1, using T-SQL The command to create a resource pool,

CREATE RESOURCE POOL, takes five optional arguments:

REQUEST_MAX_MEMORY_GRANT_PERCENT,REQUEST_MAX_CPU_TIME_SEC,GROUP_MAX_REQUESTS,

REQUEST_MEMORY_GRANT_TIMEOUT_SEC, and MAX_DOP, which were described in the preceding

section

CREATE WORKLOAD GROUP OLTPWG1

WITH ( IMPORTANCE = HIGH )

USING OLTPPool

ALTER RESOURCE GOVERNOR RECONFIGURE

GO

To view the workload groups in T-SQL, you can run a query against the

sys.resource_governor_workload_groupssystem catalog view, similar to the following,

which also displays the workload group settings:

select wg.name,

p.name as ‘pool’,

group_max_requests as max_req,

request_max_cpu_time_sec as max_cpu,

request_max_memory_grant_percent as max_mem,

request_memory_grant_timeout_sec as grant_timeout,

max_dop

from sys.resource_governor_workload_groups wg

inner join

sys.resource_governor_resource_pools p

on wg.pool_id = p.pool_id

go

name pool max_req max_cpu max_mem grant_timeout max_dop

- -

-internal -internal 0 0 25 0 0

default default 0 0 25 0 0

ReportWG1 ReportPool 0 0 25 0 0

OLTPWG1 OLTPPool 0 0 25 0 0

Creating a Classification Function

After you define your resource pools and workload groups, you need to create a

classifica-tion funcclassifica-tion that contains the logic to evaluate the connecclassifica-tions and assign them to the

appropriate workload group The classification function applies to each new session

connection to SQL Server Each session stays in the assigned workload group until it

termi-nates, unless is it reassigned explicitly to a different group There can be only one

classifi-cation function active at any given time If no classifier function is defined or active, all

connections are assigned to the default workload group

The classification function is a scalar function created with the CREATE FUNCTION

state-ment, which must return a workgroup name as value of type SYSNAME(SYSNAMEis a data

type alias for nvarchar(128)) If the user-defined function returns NULL,’default’, or the

name of nonexistent group, the session is assigned to the default workload group The

session is also assigned to the default context if the function fails for any reason

The logic of the classification function is typically based on connection properties and

often determines the workload_groupthe connection should be assigned to based on

values returned by system functions such as SUSER_NAME(),SUSER_SNAME(),

IS_SRVROLEMEMBER(),IS_MEMBER(),HOST_NAME(), or APP_NAME().In addition to these

func-tions, you can use other available property functions when making classification

deci-sions The LOGINPROPERTY()function now includes two properties (DefaultDatabaseand

DefaultLanguage) that can be used in classification functions In addition, the

CONNECTIONPROPERTY()function provides access to the network transport and protocol

being used for the connection, as well as details of the authentication scheme, the local IP

address and TCP port, and the client’s IP address For example, you could assign a

connec-tion to a workload group based on which subnet a connecconnec-tion is coming in from

TIP

If you decide to use eitherHOST_NAME()orAPP_NAME()in your classifier function, be

aware that it’s possible for the values returned by these functions to be altered by users

In general, however, theAPP_NAME()function tends to work very well for classifying

connections

TIP

A client session may time out if the classification function does not complete within

the specified time-out for the login Login time-out is a client property, and as such, the

server is unaware of a time-out A long-running classifier function can leave the server

with orphaned connections for long periods It is important that you create efficient

classifier functions that finish execution before a connection time-out

If you are using the Resource Governor, it is recommended that you enable the

dedi-cated administrator connection (DAC) on the server The DAC is not subject to

Resource Governor classification and can be used to monitor and troubleshoot a

classification function

For simplicity, the example presented in this chapter uses the SUSER_NAME()function

Listing 40.1 first creates a couple of SQL Server logins (report_userandoltp_user),

which will be used within the classification function to identify which workload group

session connections should be assigned to After adding the logins as users in the

AdventureWorks2008R2database, it then creates the classification function in the master

database

LISTING 40.1 Classification Function Example

use master;

create login report_user with password=’Rep0rter1’

create login oltp_user with password=’01tPus3r1’

go

use AdventureWorks2008R2;

create user report_user

create user oltp_user

EXEC sp_addrolemember N’db_datawriter’, N’report_user’

EXEC sp_addrolemember N’db_datareader’, N’report_user’

EXEC sp_addrolemember N’db_datawriter’, N’oltp_user’

EXEC sp_addrolemember N’db_datareader’, N’oltp_user’

go

use master

go

CREATE FUNCTION dbo.WorkgroupClassifier ()

RETURNS SYSNAME WITH SCHEMABINDING

AS

BEGIN

DECLARE @WorkloadGroup SYSNAME = N’Unidentified’;

SET @WorkloadGroup = CASE suser_name()

WHEN N’report_user’ THEN

N’ReportWG1’

WHEN N’oltp_user’ THEN

N’OLTPWG1’

ELSE N’Unidentified’

END;

RETURN @WorkloadGroup;

END;

Go

GRANT EXECUTE on dbo.WorkgroupClassifier to public

go

Before you put the classification function into use, it’s a good idea to test it A poorly

written classification function could cause your system to become unresponsive For

example, you can test the WorkgroupClassifier()function in SSMS by executing the

following commands under different login IDs:

Executed logged in as report_user

select dbo.WorkgroupClassifier()

go

-ReportWG1

Executed logged in as report_user

select dbo.WorkgroupClassifier()

go

-OLTPWG1

Executed Logged in as another user

select dbo.WorkgroupClassifier()

go

-Unidentified

After you verify the classification function works as expected, you can then configure it as

the classification function using the ALTER RESOURCE GOVERNORcommand:

ALTER RESOURCE GOVERNOR

WITH (CLASSIFIER_FUNCTION = dbo.WorkgroupClassifier);

ALTER RESOURCE GOVERNOR RECONFIGURE;

After you create the function and apply the configuration changes, the Resource Governor

classifier will use the workload group name returned by the function to send new requests

to the appropriate workload group

NOTE

You can also set the classification function for Resource Governor on the Resource

Governor Properties page, as shown in Figure 40.4 Click the Classifier Function Name

drop-down list and choose from the list of available functions presented Click OK to

save the changes and reconfigure Resource Governor

You can verify which classification function Resource Governor is currently using by

running the following query against the sys.resource_governor_configurationsystem

catalog view:

select object_name(classifier_function_id) AS ‘Classifier UDF name’,

is_enabled

from sys.resource_governor_configuration

go

Classifier UDF name is_enabled

-WorkgroupClassifier 1

At this point, your Resource Governor configuration is complete You then should

monitor the system to make sure it’s working as it should

TIP

To help make setting up and configuring Resource Governor easy and make sure you

get all the pieces together in the right sequence, you can configure Resource Governor

by using a template provided in SQL Server Management Studio From the View menu

in SSMS, select Template Explorer to display the Template Explorer In the Template

Explorer, expand Resource Governor and then double-click Configure Resource

Governor Provide the connection information, and the template Configure Resource

Governor.sqlopens in a query editor window This template contains template code

to create and configure a resource pool, workload group, and classifier function

Monitoring Resource Usage

SQL Server provides three dynamic management views you can use to view and monitor

your Resource Governor configuration:

sys.dm_resource_governor_workload_groups—Returns workload group

statistics along with the current in-memory configuration of the workload groups

sys.dm_resource_governor_resource_pools—Returns information about

current state of your resource pools and resource pool statistics

sys.dm_resource_governor_configuration—Returns the in-memory

configu-ration state of the Resource Governor Output is the same as the

sys.resource_governor_configurationsystem catalog view

For example, the following query against the sys.dm_resource_governor_resource_pools

DMV returns the configuration settings for each of the pools along with the actual

memory allocated:

select name,

min_cpu_percent as MinCPU,

max_cpu_percent as MaxCPU,

min_memory_percent as ‘MinMEM%’ ,

max_memory_percent as ‘MaxMEM%’,

max_memory_kb as ‘MaxMemKB’,

used_memory_kb as ‘UsedMemKB’,

target_memory_kb as ‘TgtMemKB’

from sys.dm_resource_governor_resource_pools

GO

name MinCPU MaxCPU MinMEM% MaxMEM% MaxMemKB UsedMemKB TgtMemKB

- - - - -

-internal 0 100 0 100 1556232 8296 1556232

default 0 100 0 100 389064 8336 389064

ReportPool 0 20 0 30 389064 280 389064

OLTPPool 80 100 75 100 1556232 40 1556232

The following example displays statistics on the requests received within the defined

workgroups:

select

cast(g.name as nvarchar(10)) as wg_name,

cast(p.name as nvarchar(10)) as pool_name,

total_request_count as totreqcnt,

active_request_count as actreqcnt,

g.total_cpu_usage_ms as tot_cpu_use,

total_cpu_limit_violation_count as tot_clvc,

g.request_max_cpu_time_sec as req_mcts,

g.total_reduced_memgrant_count as tot_rmc

from sys.dm_resource_governor_workload_groups g

inner join

sys.dm_resource_governor_resource_pools p

on p.pool_id = g.pool_id

go

wg_name pool_name totreqcnt actreqcnt tot_cpu_use tot_clvc req_mcts tot_rmc

- - -

-internal -internal 0 0 37314 0 0 0

default default 784 2 97938 0 0 0

ReportWG1 ReportPool 170 1 476016 0 0 0

OLTPWG1 OLTPPool 161 0 1834 0 0 0

Six other DMVs in SQL Server 2008 contain information related to Resource Governor:

sys.dm_exec_query_memory_grants—Returns information about the queries

that have acquired a memory grant or that still require a memory grant to execute

Resource Governor–related columns in this table are the group_id,pool_id,

is_small, and ideal_memory_kbcolumns

sys.dm_exec_query_resource_semaphores—Returns information about the

currentquery_resourcesemaphore status, providing general query-execution

memory status information The pool_idcolumn provides a link to Resource

Governor information

sys.dm_exec_session—Returns one row per session on SQL Server The group_id

column relates the information to Resource Governor workload groups

sys.dm_exec_requests—Returns information about each request currently

executing within SQL Server The group_idcolumn relates the information to

Resource Governor workload groups

sys.dm_exec_cached_plans—Returns a row for each query plan cached by SQL

Server in the plan cache The pool_idcolumn relates the information to Resource

Governor resource pools

sys.dm_os_memory_brokers—Returns information about internal allocations

within SQL Server that use the Memory Manager This information includes the

fol-lowing columns for the Resource Governor: pool_id,allocations_db_per_sec,

predicted_allocations_kb, and overall_limit_kb

The following query joins between sys.dm_exec_sessionand

sys.dm_resource_governor_workload_groupsto display which sessions are in which

workload group:

SELECT

CAST(g.name as nvarchar(10)) as poolname,

s.session_id as ‘session’,

s.login_time,

CAST(s.host_name as nvarchar(15)) as host_name,

CAST(s.program_name AS nvarchar(20)) as program_name

FROM sys.dm_exec_sessions s

INNER JOIN sys.dm_resource_governor_workload_groups g

ON g.group_id = s.group_id

where g.name in (‘default’, ‘ReportWG1’, ‘OLTPWG1’)

go

poolname session login_time host_name program_name

- - - -

-default 51 2010-05-02 14:31:18.530 LATITUDED830-W7 Microsoft SQL Server

default 52 2010-05-02 14:31:21.990 LATITUDED830-W7 SQLAgent - Generic R

default 53 2010-05-02 14:31:23.533 LATITUDED830-W7 SQLAgent - TSQL JobS

default 55 2010-05-02 14:47:27.250 LATITUDED830-W7 Microsoft SQL Server

ReportWG1 60 2010-05-02 19:06:21.100 LATITUDED830-W7 Microsoft SQL Server

OLTPWG1 54 2010-05-02 21:03:03.020 LATITUDED830-W7 Microsoft SQL Server

You can also monitor CPU and memory resources allocated by the Resource Governor

through the Windows Performance Monitor via a couple of new performance counters:

SQLServer: Resource Pool Stats

SQLServer: Workload Stats

An instance of the SQLServer: Resource Pool Statscounter is available for each of the

configured resource pools Likewise, an instance of the SQLServer: Workload Stats

counter is available for each of the configured workload groups (see Figure 40.5) These

performance counters return the same information as that returned by the

sys.dm_resource_governor_workload_groupsand

sys.dm_resource_governor_resource_poolsDMVs but enable you to monitor these

statistics over time

FIGURE 40.5 Monitoring resource pool and workload group statistics in Performance Monitor

Modifying Your Resource Governor Configuration

You can modify settings for resource pools or workload groups in SQL Server Management

Studio via the Resource Governor Properties page, as shown previously in Figure 40.4 You

simply make the changes desired (for example, a Resource Pool Maximum CPU% or

Workload Group Importance) and click OK to save the changes

Alternatively, you can modify the resource pool using the ALTER RESOURCE POOL

command With this command, you can modify the minimum and maximum CPU and

memory percentages for a resource pool The syntax is as follows:

ALTER RESOURCE POOL { pool_name | “default” }

[WITH

( [ MIN_CPU_PERCENT = value ]

[ [ , ] MAX_CPU_PERCENT = value ]

[ [ , ] MIN_MEMORY_PERCENT = value ]

[ [ , ] MAX_MEMORY_PERCENT = value ] )

]

You can modify workload group settings using the ALTER WORKLOAD GROUPcommand You

can change the workload group settings as well as move the workload group to another

resource pool The syntax is as follows:

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” } ]

NOTE

After executing yourALTER WORKLOAD GROUPorALTER RESOURCE POOLcommands,

you need to run theALTER RESOURCE GOVERNOR RECONFIGUREcommand to apply

the changes

The following example moves the ReportWG1workload group from the ReportPool

resource pool to the default resource pool:

ALTER WORKLOAD GROUP ReportWG1

USING [default];

GO