The Real MTCS SQL Server 2008 Exam 70/432 Prep Kit- P110 docx

Contracts Within the sQL service Broker a contract defines what message types can be used on a single conversation and which side of the conversation can use which message types.. When d

exerciSe 12.2

Creating MeSSage typeS

create four message types within the AdventureWorks database Use the validation NoNe for two of them and WeLL_ForMeD_xML for the other

two create the Message Types based on the data shown in Table 12.1.

Contracts

Within the sQL service Broker a contract defines what message types can be

used on a single conversation and which side of the conversation can use which

message types every conversation uses a single contract for the duration of the

conversation if you wish to use a different contract during an existing conversation

you have to close the conversation and create a new one

When defining the contract you specify which end of the conversation can use

which message type The initiator of the contract is the sender of the message, and

the target of the contract is the receiver of the message Like the Message Type,

the name of the contract can be up to 128 characters and is created using the

AUTHoriZATioN statement to assign ownership of the object to a specific user

or role within the database

When naming your contract do not name the contract with the keyword ANY

if you create a contract using the keyword ANY as the name you will not be able

to successfully assign priorities to the conversations using the creATe Broker

PrioriTY command The use of this command is outside the scope of this text;

however, you can read more on this command in Books onLine under the index

setting “creATe Broker PrioriTY statement.”

sQL service Broker contracts are created using the creATe

coNTrAcT command The creATe coNTrAcT command is very

straightforward with few options when creating the contract

Message Type Name Message Type Validation

Table 12.1 Message Types and Their validations

CREATE CONTRACT [YourApplication/Contract1]

AUTHORIZATION dbo (

[YourApplication/YourMessageType] SENT BY INITIATOR, [AnotherApplication/AnotherMessageType] SENT BY TARGET );

When looking at this example code, you can begin to see why the naming conventions shown here can make it quite a bit easier to see which sQL service Broker objects go with which Application

Exam Warning

pay special attention to the SeNT BY options in the exam The various options can get confusing during the exam Also pay attention to the wording of the questions.

if you wish to create a contract that uses the same Message Type for both the initiator and the target either you can specify the Message Type twice as done above, or you can specify that the Message Type be sent by ANY as shown here CREATE CONTRACT [YourApplication/Contract1]

AUTHORIZATION dbo

(

[YourApplication/YourMessageType] SENT BY ANY, );

either syntax is perfectly acceptable, and neither is incorrect

There is no ALTer coNTrAcT command in sQL server 2005 or sQL server 2008; perhaps this command will make it into a future version This prevents you from adding or removing a Message Type from the contract after the contract has been created The only way to add or remove a Message Type from a contract is

to create a new contract, modify all services that reference that contract to use the new contract, and then remove the original contract from the database using the DroP coNTrAcT command

There is no easy way to see after creating the contracts which Message Types are contained within the contracts You can manually right-click on each contract

in the object explorer and script each object out in a large sQL service

Broker environment this could take hours or days to the sQL server database Because of this, having a good knowledge of the sQL service Broker catalog

views is extremely important You will find the meta data about the Message Types

in the sys.service_message_types catalog view, and the meta data about the contracts

in the sys.service_contracts catalog view The linking view between these two

catalog views is the sys.service_contract_message_usages catalog view This view

contains the id of the contract and the Message Type, as well as bit flags for which

end of the conversation can use the message type

in sQL server 2008 a properties screen was introduced, which will allow you to view the contract and see what Message Types are bound to the contract However,

there is no way to view which contracts are bound to which Message Types

eXerCiSe 12.3

create two contracts each contract should be bound to both message

types Use the chart shown in Table 12.2 when creating your contracts.

Queues

The sQL service Broker queue is where the messages are sent to and

received from You can think of them as kind of like tables, except that you cannot

change the structure of them Just like a table you can select data from the queue,

and doing so will not affect the messages within the queue However, because this is

a sQL service Broker queue and not a table you cannot iNserT, UPDATe,

or DeLeTe any of the data within the queues Because queues are physical objects

created within the database, you can specify a database schema that contains the

object, however, it is most common to leave the queue in the dbo schema As the

queue is a physical object that stores the messages that are sent to it, you will need to

specify the sQL server File Group that will store the data from the messages in it

Contract Name Message Types

MT_ xML

MT_ xML

Table 12.2 contracts and Message Types

When creating the sQL service Broker queues you have several options from which you can select You can enable or disable the queue from receiving messages via the sTATUs option You can tell the sQL service Broker to keep messages after they have been received or to delete them after they have been received via the reTeNTioN flag You also have the option of having a stored procedure be run by the sQL service Broker by using the AcTivATioN settings By default the sTATUs setting will be enabled, and the reTeNTioN setting will be disabled The AcTivATioN setting will be enabled by default, however, without the procedure name set no action will be taken until you specify the name of the stored procedure to execute This procedure, if specified, must exist Therefore, it is recommended that you create the queue, then the procedure that will read from the queue, then use the ALTer QUeUe command to set the activation procedure With the exception of setting the file group all options that are available

in the creATe QUeUe command are available in the ALTer QUeUe command Activated stored procedures are probably one of the most important parts of the sQL service Broker system They allow the sQL server to automatically start a stored procedure when a message arrives so that messages can be processed as quickly as possible You can even control how many copies of the stored procedure are running—from a single thread up to 32,767 threads You will want to be very careful with how high you set this setting since setting it too high could cause your sQL server cPU to increase as you add thousands of threads to the system

Configuring & Implementing…

Message Queues in the Real World

SQL Service BroKer is used by many companies in many different ways pretty much anything that doesn’t need to give data back to the user can

be set up to go through the SQL Service BroKer This gives the user a faster experience since the user interface does not have to wait for the process to be completed Some of the various things that can be done with the SQL Service BroKer include data logging, Windows service to Windows service messages, and physical file manipulation.

Continued

When you increase the number of threads that the Queue will run in parallel

and there are already messages in queue, the new threads will normally start within

a few seconds When you reduce the number of threads, no threads are halted at

that time The threads must stop on their own by running out of messages to

process No new threads will be started, but there will be more threads running

than are configured until those threads begin to end

The same effect occurs if you stop the activation No new threads will be started but the running threads will continue to process until they run out of messages to

process if you change the procedure name of the activated procedure then the new

procedure name will not be used until there is room for a new thread to be started

in the number of threads running if you have the queue configured for five threads

and there are five threads running when you change the procedure name, the new

procedure will not be used until after one thread has stopped At this time the new

procedure name will be used when the new thread is started if you need to stop

all the activated procedures from processing any additional messages then you will

want to disable the queue, which will prevent the activated procedures from receiving any new messages out of the queue, causing the procedures to exit after they have

finished processing the current message

Using an example let’s look at how the queue is going to handle the activated

stored procedure First, we will make a few assumptions about the dbo.YourProcedure

procedure and the queue

1 The procedure dbo.YourProcedure contains a loop that will attempt to

process all the messages in the queue in a single execution of the procedure

in systems where each record has a physical file assigned to it, you can

set up a trigger, and when the records are deleted, a SQL Service BroKer

message is sent containing the files that need to be deleted A Windows

service can then receive the messages in the queue and delete the physical

files The same can be done when files need to be moved from one place

to another When the record is updated, an update trigger on the table

fires and sends a message to the SQL Service BroKer The message is then

downloaded by a Windows service, which then moves the physical file.

Many companies have all sorts of data logging going on either

within the internal application, or within the web server to track site

usage This allows the web site to log data about the site usage, without

having to wait for the database to process the insert or any rollups that

are done based on the insert.