Microsoft SQL Server 2008 R2 Unleashed- P235 pps

The following is an example of this option: exec sp_configure ‘min memory per query’, 2048 go RECONFIGURE go Looking back at Figure 55.5 showing the Memory page of the Server Properties

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ptg FIGURE 55.5 The minimum server memory and maximum server memory configuration

settings in SSMS

max text repl size

Type: Basic

Default value: 65536

Themax text repl sizeparameter specifies the maximum size of the text,ntext,

varchar(max),nvarchar(max), and imagedata types for columns participating in

replica-tion during single insert,update,writetext, and updatetextstatements You might need

to raise this value if the image sizes your application deals with are consistently large and

the data is part of a replication configuration

The following is an example of this option:

exec sp_configure ‘max text repl size’, 131072

go

RECONFIGURE

go

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max worker threads

Type: Basic

SQL Server uses native operating system threads The max worker threadsparameter

spec-ifies the maximum number of threads available for SQL Server processes One or more

threads are used for supporting each network protocol (for example, TCP/IP, named pipes)

SQL Server is configured to listen The checkpoint and lazywriter processes also consume

threads A pool of threads is used to handle user connections When the number of

connections is lower than the max worker threadsparameter value, a thread is created for

each connection When more connections are on the server than the value defined by the

max worker threadsparameter, SQL Server provides thread pooling for efficient resource

utilization The default value of 0autoconfigures the number of max worker threadsto

be (256 + ((number of processors – 4) × 8)) for a 32-bit processor and twice that for a

64-bit processor So, for an 8 processor 32-64-bit machine, the max worker threads value would

be autoconfigured to be (256 + ((8 – 4) × 8)) = 288

More threads can create overhead on the system processors Therefore, lowering this value

might sometimes improve the performance of a system For a system with a few hundred

user connections, a reasonable value for this parameter is 288 You might want to

experi-ment with various values to determine the appropriate setting for this parameter A

multi-processor environment can easily handle more threads, and you can increase the number

of threads accordingly

exec sp_configure ‘max worker threads’, 288

go

RECONFIGURE

go

The following is a general recommendation of what to specify based on the different

application types you are running:

OLTP—For multiprocessor environments, set the value upward because those

envi-ronments can handle servicing more threads This yields performance gains

Data warehouse—Use the default value, 0

OLAP—Use the default value, 0

Mixed—For multiprocessor environments, set the value upward because those

envi-ronments can handle servicing more threads This yields performance gains

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min memory per query

Type: Advanced

Themin memory per queryoption specifies the minimum amount of memory that will be

allocated for the execution of a query Normally, the SQL Server query processor attempts

to determine the optimal amount of memory for a query This option allows the sysadmin

role to specify this value instead Increasing this value usually improves queries that

handle hash and sort operations on a large volume of data

exec sp_configure ‘min memory per query’, 2048

go

RECONFIGURE

go

Looking back at Figure 55.5 showing the Memory page of the Server Properties dialog, you

can see the min query memory per queryoption set at 1024(the default)

OLTP—Use the default value, 1024

Data warehouse—This is a good opportunity to better service numerous canned

queries in this environment Set the value higher than the default

Mixed—Use the default value, 1024

nested triggers

Type: Basic

As the name suggests, nested triggersspecifies whether a trigger event on a table will

fire another trigger (that is, cascade) The nesting level of triggers is 32 If you reach this

limit of 32, SQL Server gives an error and rolls back the transaction The default value of 1

means that a trigger on a table can cause another trigger to fire

network packet size

Type: Basic

Thenetwork packet sizeparameter specifies the default network packet size for SQL

Server Setting this value to a higher number (which should be divisible by 512) can

improve the performance of applications that involve a large amount of data transfer from

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the server Check your network configuration and set an appropriate value for this

para-meter You can also improve performance by lowering the size value for applications that

are small in data transfer size However, the usual scenario is to increase this size to

accommodate large amounts of data transfer, as with bulk loads

exec sp_configure ‘network packet size’, 8192

go

RECONFIGURE

go

TIP

You can also specify the network packet size from the client when you connect to SQL

Server (using the -aoption for isql,osql, and bcp) Setting the network packet size

from a client can be useful when the default network packet size is adequate for

gener-al application needs However, a larger packet size might be needed for some specific

operations, such as bulk copy You can also call OLE DB, ODBC, and DB-Library

func-tions to change the packet size

OLTP—Possibly decrease this size to 512if all queries deal with small amounts of

data transfer, which is often the case in OLTP or ATM applications

Data warehouse—Perhaps increase this to 8192or larger to handle the consistently

large data transfers in this environment

optimize for ad hoc workloads

Type: Advanced

Theoptimize for ad hoc workloadsoption is used to improve the efficiency of the

plan/procedure cache for workloads that contain many single-use ad hoc batches When

this option is set to 1, the Database Engine stores a small compiled plan stub in the

plan/procedure cache when a batch is compiled for the first time, instead of the full

compiled plan This helps to relieve memory pressure by not allowing the plan/procedure

cache to become filled with compiled plans that are not reused The compiled plan stub

allows SQL Server to recognize that this ad hoc batch has been compiled before but has

stored only a compiled plan stub, so when this batch is invoked (compiled or executed)

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again, SQL Server compiles the batch, removes the compiled plan stub from the

plan/procedure cache, and adds the full compiled plan to the plan/procedure cache

Settingoptimize for ad hoc workloadsto1affects only new plans; plans that are

already in the plan/procedure cache are unaffected The compiled plan stub is one of the

cache object types displayed by the sys.dm_exec_cached_planscatalog view

exec sp_configure ‘optimize for ad hoc workloads’,1

go

RECONFIGURE

go

PH_timeout

Type: Advanced

You use the full-text protocol handler timeout option (PH timeout) to specify the time, in

seconds, that the handler should wait to connect to a database before timing out The

default value is 60 seconds Increase the value when connection attempts are timing out

due to temporary network issues or increased workloads The full-text protocol handler is

hosted in the filter daemon host and is used to fetch the data to be full-text indexed

exec sp_configure ‘PH_timeout’, 120

go

RECONFIGURE

go

priority boost

Type: Advanced

Thepriority boostoption is used to specify the process priority of SQL Server processes

on the Windows operating system The default value of 0means that SQL Server should

run on the same priority level—a priority base of 7—as other applications on the machine

This option can be turned on if you have plenty of horsepower to deal with all other

services on the box, as in a multiprocessor environment When you turn on priority

boost, the priority base of SQL Server is elevated to 13

exec sp_configure ‘priority boost’, 1

go

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RECONFIGURE

go

NOTE

You shouldn’t set the value of the priority boostparameter to 1except in the case

of a dedicated SQL Server machine with multiprocessors

Looking back at Figure 55.3, you can see the Boost SQL Server Priority on Windows option

in the Processors page of the Server Properties dialog Use care when applying this option

query governor cost limit

Type: Advanced

Queries are often the cause of major performance problems SQL Server can handle

queries, but many are poorly written and don’t restrict the search criteria enough This

can result in runaway queries that return large result sets, and they can adversely affect

the entire server’s performance One way to control this situation is to cut off the query at

the pass by specifying a maximum cost limit to queries, in seconds If any query’s cost, in

seconds, is greater than this maximum value, the query is not allowed to execute The

query governor cost limitvalue is server-wide and cannot be applied to just one query

Remember, though, that 0(the default) for this option turns off the query governor, and

all queries are allowed to run without any time limitation

exec sp_configure ‘query governor cost limit’, 300

go

RECONFIGURE

Go

To change the value on a per-connection basis, you use the SET

QUERY_GOVERNOR_COST_LIMITstatement

Data warehouse—This is a must-have option for this environment Try setting this

value to 300seconds and then get ready for the users to scream at you On the

posi-tive side, the server won’t get bogged down or freeze again

OLAP—For OLAP systems that use SQL Server storage, set this value to 600seconds

to get started and then reduce it over time

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Mixed—You have the same protection opportunity here as for OLAP This won’t

affect the OLTP queries, so it is safe to apply

query wait

Type: Advanced

Default value: -1

Queries that are memory intensive and involve huge sorts might take a long time to

execute, based on the available memory during execution SQL Server internally calculates

the timeout interval for such queries Usually, this is quite a large number You can

over-ride this value by specifying a value (in seconds) for the query waitparameter in SQL

Server If you set this value too low, you risk more frequent query timeouts when your

system is under a heavy load and a highly concurrent environment If -1is specified (the

default), the timeout is calculated as 25 times of the estimated query cost

exec sp_configure ‘query wait’, 20

go

RECONFIGURE

go

recovery interval

Type: Advanced, self-configuring

Therecovery intervalparameter is used to specify the maximum time (in minutes) that

SQL Server requires to recover a database during startup During startup, SQL Server rolls

forward all the changes committed during a SQL Server crash and rolls back the changes

that were not committed Based on the value specified for this parameter, SQL Server

determines when to issue a checkpoint in every database of SQL Server so that in the

event of a crash, SQL Server can recover the databases in the time specified by recovery

interval If the value of the recovery intervalparameter is low, SQL Server issues

check-points more frequently to allow a recovery to be faster; however, frequent checkcheck-points can

slow down performance Setting recovery intervaltoo high creates a longer recovery

time for databases in the event of a crash The default value of 0leaves this option open

to SQL Server to determine the best value

exec sp_configure ‘recovery interval’, 10

go

RECONFIGURE

go

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Data warehouse—This is an opportunity to save on checkpoints and not degrade

performance in this mostly read-only environment Set this value high

OLAP—In this read-only environment, you have the same performance opportunity

here as in a data warehouse

remote admin connections

Type: Basic

Microsoft SQL Server 2008 provides a dedicated administrator connection (DAC) The

DAC lets an administrator access a running server to be able to execute diagnostic

func-tions or T-SQL statements, or troubleshoot problems on the server, even when the server is

locked or running in an abnormal state and not responding to any other type of user

connection By default, the DAC is available only from a client on the server But if you

set the Remote Admin connectionsoption to 1, the DAC is available from a remote

connection as well By default, the DAC listens only on the loopback IP address

(127.0.0.1), port 1434

exec sp_configure ‘remote admin connections’, 1

go

RECONFIGURE

Go

remote login timeout

Type: Basic

You use theremote login timeoutoption to specify the number of seconds to wait

before returning from a failed attempt to log in to a remote server If you are attempting

to log in to a remote server and that server is down,remote login timeoutensures that

you do not have to wait indefinitely before your computer ceases its attempts to log in

This option affects connections to OLE DB providers made for heterogeneous queries

The default setting for remote login timeout is20(seconds) A value of0allows for an

infinite wait

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exec sp_configure ‘remote login timeout’, 30

go

RECONFIGURE

Go

remote proc trans

Type: Basic

Theremote proc transparameter allows remote procedures that are taking part in

multi-server transactions to use MS DTC so that transaction integrity is maintained across

servers The default value of 0means the remote procedure calls will not use MS DTC

Data modification at the remote server will not be a part of transactions at the local server

If you set this parameter to 1, SQL Server uses MS DTC to preserve transaction integrity

across servers This feature is still scheduled to be removed in the next version of

Microsoft SQL Server You should therefore avoid using this feature in new development

work and plan to modify applications that currently use this feature

exec sp_configure ‘remote proc trans’, 1

go

RECONFIGURE

Go

remote query timeout

Type: Basic

You use theremote query timeoutoption to specify how long (in seconds) a remote

opera-tion can take before Microsoft SQL Server times out The default is600, which allows a

10-minute wait This value applies to an outgoing connection initiated by the Database Engine

as a remote query This value has no effect on queries received by the Database Engine

For heterogeneous queries, remote query timeoutspecifies the number of seconds

(initial-ized in the command object using the DBPROP_COMMANDTIMEOUTrowset property) that a

remote provider should wait for result sets before it times out This value is also used to set

DBPROP_GENERALTIMEOUT, if supported by the remote provider This setting causes any

other operations to time out after the specified number of seconds

For remote stored procedures,remote query timeoutspecifies the number of seconds

that must elapse after sending a remoteEXECstatement before the remote stored

proce-dure times out

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exec sp_configure ‘remote query timeout’, 300

go

RECONFIGURE

Go

scan for startup procs

Type: Advanced

When the scan for startup procsoption is set to 1, SQL Server scans for and executes

all automatically executed stored procedures on the server on startup To set a stored

procedure to become automatically executed, you use the sp_procoptionsystem stored

procedure Typically, a stored procedure is executed at startup time when you want to

have certain processing occur that creates the proper working environment for all

subse-quent database processing on the server You also can execute at startup when you want to

make sure that certain stored procedures’ execution plans (with proper optimizer

deci-sions) are already in the procedure cache before anyone else requests their execution

exec sp_configure ‘scan for startup procs’, 1

go

RECONFIGURE

go

show advanced options

Type: Basic

By default, you do not see the advanced configuration parameters of SQL Server If you set

show advanced optionsto1, you can see all the SQL Server parameters that can be set by

thesp_configurecommand

user connections

Type: Advanced, self-configuring

Theuser connectionsoption specifies the number of concurrent users allowed on SQL

Server When the value is0(which is the default), SQL Server can configure the needed

user connections dynamically as they are needed (unlimited) If you specify a value, you

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