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The Transaction mediator supports distributed transactions using the Java transaction API (JTA). When it comes to distributed transactions, it involves accessing and updating data on two or more networked computers, often using multiple databases. For example, two databases or a database and a message queue such as JMS. You can use the Synapse configuration language to define when to start, commit, or roll back the transaction. For example, you can mark the start of a transaction at the start of a database commit, mark the end of the transaction at the end of database commit and roll back the transaction if an error occurs.

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Copy and paste the following configuration into <EI_HOME>/repository/deployment/server/synapse-configs/<node>/synapse.xml.
The sample configuration used here is similar to sample 361. Here via the In sequence a message is sent to the service, and via the Out sequence an entry from the first database is deleted and the second database is updated with that entry. If an entry that already exists is added once again to the second database, the entire transaction will roll back.

Code Block

	XML
	XML

<definitions xmlns="http://ws.apache.org/ns/synapse">
   <sequence name="myFaultHandler">
        <log level="custom">
            <property name="text" value="** Rollback Transaction**"/>
        </log>
        <transaction action="rollback"/>
        <send/>
    </sequence>
    <sequence name="main" onError="myFaultHandler">
        <in>
            <send>
                <endpoint>
                    <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
                </endpoint>
            </send>
        </in>
         <out>
            <transaction action="new"/>
            <log level="custom">
                <property name="text" value="** Reporting to the Database EIdb**"/>
            </log>
            <dbreport useTransaction="true" xmlns="http://ws.apache.org/ns/synapse">
                <connection>
                    <pool>
                        <dsName>java:jdbc/XADerbyDS</dsName>
                        <icClass>org.jnp.interfaces.NamingContextFactory</icClass>
                        <url>localhost:1099</url>
                        <user>EI</user>
                        <password>EI</password>
                    </pool>
                </connection>
                <statement>
                     <sql>delete from company where name =?</sql>
                     <parameter expression="//m0:return/m1:symbol/child::text()"
                       xmlns:m0="http://services.samples" xmlns:m1="http://services.samples/xsd"
                                 type="VARCHAR"/>
                </statement>
            </dbreport>
            <log level="custom">
                <property name="text" value="** Reporting to the Database EIdb1**"/>
            </log>
            <dbreport useTransaction="true" xmlns="http://ws.apache.org/ns/synapse">
                <connection>
                    <pool>
                        <dsName>java:jdbc/XADerbyDS1</dsName>
                        <icClass>org.jnp.interfaces.NamingContextFactory</icClass>
                        <url>localhost:1099</url>
                        <user>EI</user>
                        <password>EI</password>
                    </pool>
                </connection>
                <statement>
                    <sql>INSERT into company values (?,'c4',?)</sql>
                    <parameter expression="//m0:return/m1:symbol/child::text()"
         xmlns:m1="http://services.samples/xsd" xmlns:m0="http://services.samples"
                               type="VARCHAR"/>
                    <parameter expression="//m0:return/m1:last/child::text()"
         xmlns:m1="http://services.samples/xsd" xmlns:m0="http://services.samples"
                               type="DOUBLE"/>
                </statement>
            </dbreport>
            <transaction action="commit"/>
            <send/>
        </out>
    </sequence>
</definitions>

Setup two distributed Derby databases EIdb and EIdb1. For instructions on setting up the Derby databases, see Setting up the Derby database server /wiki/spaces/EI6xx/pages/49610865.

Create a table in EIdb by executing the following statement.

Code Block

	SQL
	SQL

CREATE table company(name varchar(10) primary key, id varchar(10), price double);

Create a table in EIdb1 by executing the following statement.

Code Block

	SQL
	SQL

CREATE table company(name varchar(10) primary key, id varchar(10), price double);

Insert records into the two tables that you created by executing the following statements.
To insert records into the table in EIdb
Code Block
SQL
SQL
INSERT into company values ('IBM','c1',0.0); INSERT into company values ('SUN','c2',0.0);
To insert records into the table in EIdb1
Code Block
SQL
SQL
INSERT into company values ('SUN','c2',0.0); INSERT into company values ('MSFT','c3',0.0);
Info
title Note
When inserting records into the tables, the order of the record matters.

Create the following data source declarations for the distributed databases in the <EI_HOME>/conf/datasources/master-datasources.xml file.

Code Block

	XML
	XML

<datasources>
    <xa-datasource>
        <jndi-name>jdbc/XADerbyDS</jndi-name>
        <isSameRM-override-value>false</isSameRM-override-value>
        <xa-datasource-class>org.apache.derby.jdbc.ClientXADataSource</xa-datasource-class>
        <xa-datasource-property name="portNumber">1527</xa-datasource-property>
        <xa-datasource-property name="DatabaseName">EIdb</xa-datasource-property>
        <xa-datasource-property name="User">EI</xa-datasource-property>
        <xa-datasource-property name="Password">EI</xa-datasource-property>
        <metadata>
            <type-mapping>Derby</type-mapping>
        </metadata>
    </xa-datasource>
</datasources>

Code Block

	XML
	XML

<datasources>
    <xa-datasource>
        <jndi-name>jdbc/XADerbyDS1</jndi-name>
        <isSameRM-override-value>false</isSameRM-override-value>
        <xa-datasource-class>org.apache.derby.jdbc.ClientXADataSource</xa-datasource-class>
        <xa-datasource-property name="portNumber">1527</xa-datasource-property>
        <xa-datasource-property name="DatabaseName">EIdb1</xa-datasource-property>
        <xa-datasource-property name="User">EI</xa-datasource-property>
        <xa-datasource-property name="Password">EI</xa-datasource-property>
        <metadata>
            <type-mapping>Derby</type-mapping>
        </metadata>
    </xa-datasource>
</datasources>

Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services /wiki/spaces/EI6xx/pages/49610865.
Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server /wiki/spaces/EI6xx/pages/49610865.

Testing the example scenario

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Execute the following command from the <EI_HOME>/samples/axis2Client directory.
Code Block
ant stockquote -Daddurl=http://localhost:9000/services/SimpleStockQuoteService -Dtrpurl=http://localhost:8280/ -Dsymbol=IBM
Executing this command removes the IBM record from the first database and adds it to the second database.
When you check both databases you will see that the IBM record is deleted from the first database and added to the second database.

To test the f ailure scenario

Execute the following command from the <EI_HOME>/samples/axis2Client directory.
Code Block
ant stockquote -Daddurl=http://localhost:9000/services/SimpleStockQuoteService -Dtrpurl=http://localhost:8280/ -Dsymbol=SUN
Executing this command attempts to add an already existing record again to the second database, which results in the fault sequence being executed. You will see an exception raised for duplicate entries and the entire transaction will roll back.
When you check both databases you will see that a record is neither deleted from the first database nor added into the second database.

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Testing the example scenario