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

PerformanceTuning•Chapter13 597
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

598 Chapter13•PerformanceTuning
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
Pool Min % Max %
Calculated
Effective
Max %
Calculated
Shared %
Effective
Max
Calculation
Explained
Shared %
Calculation
Explained

Internal 0 100 100 0 Not
applicable
to internal
pool
Not
applicable
to internal
pool
Default 0 100 50 50 min(100,
100–50) = 50
50–0=50
Pool-A 10 100 60 50 min(100,
100–40) = 60
60–10=50
Pool-B 35 90 85 10 min(90,
100–15) = 85
85–35=10
Pool-C 5 70 55 50 min(80,
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

PerformanceTuning•Chapter13 599
(MAX_CPU_PERCENT=50,
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:
600 Chapter13•PerformanceTuning
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.
PerformanceTuning•Chapter13 601
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.