The Real MTCS SQL Server 2008 Exam 70/432 Prep Kit- P124 pptx

The Resource Governor was introduced to SQL Server 2008 to provide predictable performance for mission-critical workloads.. Resource Governor achieves predictable performance by monitor

customers, realizing many benefits of better hardware utilization and more

cost-effective database deployments However consolidation does have some drawbacks

The most common objections to server consolidation is performance, because shared (multi-instance) servers and shared SQL Server instances can introduce challenges in

ensuring consistent performance for all database users Common problems arise from mixed users where regular OnLine Transaction Processing (OLTP) users mix with

reporting users on the same instance; examples can be found where databases for the

finance department combine with sales order databases In this situation, normal

database traffic consisting of inserts, updates, and deletes can conflict with the

work-load generated by reports run by finance users executing month- or year-end reports based on historic sales data

The Resource Governor was introduced to SQL Server 2008 to provide

predictable performance for mission-critical workloads Resource Governor

achieves predictable performance by monitoring and reserving minimum levels of

critical resources such as CPU and memory for specific tasks or groups of tasks

Resource Governor Concepts

The Resource Governor consists of three key concepts: Resource Pools, Workload

Groups, and Classification Functions The Resource Governor exists to manage

minimum resources available for different groups of users or tasks However the

governor is more intelligent than simply dividing resources among users; if resources

are unused elsewhere on a server, a given user can be permitted to use excess of their

quota (up to a maximum allocation) until a time when another user or process

requires the resource (memory or CPU)

This section introduces each concept and uses an example to illustrate the purpose and implementation of the concept The example relates to a college whereby requests

from lecturers should receive priority over requests received from students

Resource Pools

Resource pools are used to manage minimum and maximum restrictions on physical server resources Conceptually, Resource Pools enable multiple virtual SQL Server

instances to operate within a single physical instance Each pool (virtual instance)

is allocated a minimum and maximum CPU and memory resources There is a limit

of 18 custom resource pools in addition to the two resource pools created when

SQL Server 2008 is installed:

INTERNAL: Use for SQL Server internal system processes

■

■

DEFAULT: Used by workloads unassigned to any workload group

■

■

The combination of minimum values across all pools cannot exceed 100% and the maximum value can be anywhere between the minimum value and 100% In addition to Min and Max settings, Resource pools have two further calculated val-ues; Effective Maximum and Shared % (see Table 13.10) The Effective Maximum is determined by calculating the max value of a Resource pool and the minimum values of all other Resource pools The internal pool has highest priority of all Resource pools since this is where internal processes are handled; it is not exposed

to effective or share maximums

Resource

Calculated Effective Max % Calculated Shared %

Effective Max Calculation Explained

Shared % Calculation Explained

applicable

to internal pool

Not applicable

to internal pool

100–50) = 50 50–0=50

100–40) = 60 60–10=50

100–15) = 85 85–35=10

100–45) = 55 55–5=50

Table 13.10 Resource Pool Calculated Values

The following T-SQL can be used to create two resource pools, the first for lecturers and the second for students:

CREATE RESOURCE POOL rscpLecturers

WITH

( MAX_CPU_PERCENT = 100,

MIN_CPU_PERCENT = 50)

GO

CREATE RESOURCE POOL rscpStudents

WITH

MIN_CPU_PERCENT = 0)

GO

Workload Groups

The Workload Group makes managing the Resource Governor easier The

Workload Group makes it easier to assign user session requests to a specific

resource pool Workload groups also make it easier to monitor resource consumption within each Resource pool Workload groups may be moved between Resource

pools by the administrator if a particular Resource pool becomes too busy or

overloaded

Similar to Resource pools, administrators can create their own Workload

Groups and there are two groups created when SQL Server is installed:

INTERNAL: Use for internal SQL Server operations

■

■

DEFAULT: All unassigned session requests are serviced by this

■

■

workload group

Here’s the T-SQL required to create a group for two workload groups:

CREATE WORKLOAD GROUP grpLecturers

WITH

(IMPORTANCE = MEDIUM)

CREATE WORKLOAD GROUP grpStudents

WITH

(IMPORTANCE = LOW)

Classification Function

The classification function is created to identify incoming requests to SQL Server

and map these incoming requests to a workload group The classification function is

a user-defined function (UDF) and is created as a scalar valued function The

function can use any valid property to classify a new session, such as Username,

Hostname, or IP address

Only one UDF can be designated as a classifier at any one time Consider

performance of the UDF when creating the function since it will be used to

evaluate every incoming session The Dedicated Administrator Connection

(DAC) is not exposed to classification; as such the DAC can be used to

trouble-shoot performance problems relating to classification Once the classifier function

has been defined, it should be assigned to the Resource Governor, followed by

the reconfigure statement:

ALTER RESOURCE GOVERNOR

WITH (CLASSIFIER_FUNCTION = dbo.func_Session_Classifier)

Configuring & Implementing…

Always Enable DAC

When Using Resource Governor

All new sessions are subject to the classification function Enable Dedicated Admin Connection to provide access for troubleshooting since this connection

is not subject to classification.

Validate Configuration

The Resource Governor should be enabled before use (is disabled by default) Configuration changes can be made dynamically and don’t require a service restart, however the following instruction should be used after any changes to bring these into effect:

ALTER RESOURCE GOVERNOR RECONFIGURE

Use the following DYNAMIC Management Views (DMVs) to verify configuration

is as intended:

sys.dm_resource_governor_resource_pools

sys.dm_resource_governor_workload_groups

Resource Governor Summary

The Resource Governor is an important new feature to manage resource allocation among groups of users The following simplified pseudo-steps illustrate the process an incoming session steps through in order to be allocated resources by the governor:

1 Session begins

2 Classification function executes

3 Workload Group membership determined; otherwise use Default

4 Query executes within specified resource pool

Summary of Exam Objectives

This chapter provided an overview of performance tuning in SQL Server 2008,

including an introduction to tracing with SQL profiler, an overview of locking and

blocking, the basics of Dynamic Management Views and Performance Data

Collection Additionally we looked at how the Resource Governor can be used to

manage mixed workloads to ensure minimum resource availability

We also looked at table partitioning – a technology useful when maintenance

(backup, reindexing, checkdb) become cumbersome with particularly large tables

Partitioning provides the option to separate a large table into a number of smaller

tables – which is completely transparent to the application

Exam Objectives Fast Track

Tracing

Use SQL Profiler to capture the statements being executed on a server for

Ü

performance review/ analysis

There can be an overhead with running traces, consider how many events

Ü

you capture, any filters you apply and where the trace is run

Trace data saved directly to a database or to a file then imported into a

Ü

database for easier analysis

Locks, Blocking, and Deadlocks

Locking and blocking is normal in a database – but if frequency is excessive

Ü

they can lead to performance problems

Deadlocks are always damaging for performance – use SQL Profiler to

Ü

capture a trace or enable traceflag 1222 for more details about the processes

involved in deadlocking, then address the cause

Consider the transaction isolation level and indexing to ensure processes

Ü

use appropriate locking mechanisms based on their requirements

Guide to the Dynamic Management Views

DMVs and Dynamic Management Functions (DMFs) provide a view on

Ü

SQL Server internals and can be used for troubleshooting and fault diagnosis