Sample 657: Distributed Transaction Management

Introduction

This sample demonstrates the functionality of the Transaction Mediator using a sample distributed transaction. In this sample, a record is deleted from one database and added to a second database. If either of the operations (deleting from the first database and adding to the other) fails, all operations rollback, and the records do not change.

Prerequisites

• For a list of general prerequisites, see Setting Up the ESB Samples.
• The sample configuration uses two datasources and database instances to point to the sample databases. You have to manually create these in your environment for the sample to work.

  • Setup two distributed Derby databases  esbdb and  esbdb1.  For instructions on setting up the Derby databases, see Setting up Remote Derby.

  • Create a table in esbdb by executing the following statement.

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

  • Create a table in esbdb1 by executing the following statement.

    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 esbdb

    INSERT into company values ('IBM','c1',0.0);
    INSERT into company values ('SUN','c2',0.0);
    

    To insert records into the table in esbdb1

    INSERT into company values ('SUN','c2',0.0);
    INSERT into company values ('MSFT','c3',0.0);
    

    Note

    When inserting records into the tables, the order of the record matters.

  • Add the required datasource via the Management Console or create datasource declarations for the distributed databases In the master-datasources.xml file. For information on how you can add datasources via the management console, see Adding Datasources.  To create datasource declarations In the  master-datasources.xml  file, add the following code segments in the  master-datasources.xml  file located in the < ESB_HOME>/repository/conf/datasources  directory, ensuring that the datasource file names are  *-xa-ds.xml :
    Datasource1: esb-derby-xa-ds.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">esbdb</xa-datasource-property>
            <xa-datasource-property name="user">esb</xa-datasource-property>
            <xa-datasource-property name="password">esb</xa-datasource-property>
            <metadata>
                <type-mapping>Derby</type-mapping>
            </metadata>
        </xa-datasource>
    </datasources>
    

    Datasource2: esb-derby1-xa-ds.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">esbdb1</xa-datasource-property>
            <xa-datasource-property name="user">esb</xa-datasource-property>
            <xa-datasource-property name="password">esb</xa-datasource-property>
            <metadata>
                <type-mapping>Derby</type-mapping>
            </metadata>
        </xa-datasource>
    </datasources>
    

Building the sample

The XML configuration for this sample is as follows: 

<definitions xmlns="http://ws.apache.org/ns/synapse"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://ws.apache.org/ns/synapse http://synapse.apache.org/ns/2010/04/configuration/synapse_config.xsd">
    <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 esbdb**"/>
            </log>
            <dbreport useTransaction="true" xmlns="http://ws.apache.org/ns/synapse">
                <connection>
                    <pool>
                        <dsName>jdbc/XADerbyDS</dsName>
                        <user>esb</user>
                        <password>esb</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 esbdb1**"/>
            </log>
            <dbreport useTransaction="true" xmlns="http://ws.apache.org/ns/synapse">
                <connection>
                    <pool>
                        <dsName>jdbc/XADerbyDS1</dsName>
                        <user>esb</user>
                        <password>esb</password>
                    </pool>
                </connection>
                <statement>
                    <sql>INSERT into company values ('IBM','c4',12.0)</sql>
                </statement>
            </dbreport>
            <transaction action="commit"/>
            <send/>
        </out>
    </sequence>
</definitions>

This configuration file synapse_sample_657.xml is available in the <ESB_HOME>/repository/samples directory.

To build the sample

1. Start the ESB with the sample 657 configuration. For instructions on starting a sample ESB configuration, see Starting the ESB with a sample configuration.

   The operation log keeps running until the server starts, which usually takes several seconds. Wait until the server has fully booted up and displays a message similar to "WSO2 Carbon started in n seconds."

2. Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.

3. Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services.

You now have a running ESB instance, databases and a back-end service deployed in your environment.

Executing the sample

The sample client used here is the Stock Quote Client, which can operate in several modes. For further details on this sample client and its operation modes, see Stock Quote Client.

To execute the sample client

• Execute the following command from the <ESB_HOME>/samples/axis2Client directory to test the successful scenario.

  ant stockquote -Daddurl=http://localhost:9000/services/SimpleStockQuoteService
  -Dtrpurl=http://localhost:8280/ -Dsymbol=IBM

• Execute the following command from the <ESB_HOME>/samples/axis2Client directory to test the failure scenario.

  ant stockquote -Daddurl=http://localhost:9000/services/SimpleStockQuoteService
  -Dtrpurl=http://localhost:8280/ -Dsymbol=SUN

Analyzing the output

When you run the client to test the successful scenario, you will see that the IBM record is removed from the first database and added to the second database.

When you run the client to test the failure scenario, you will see that a record is neither deleted from the first database nor added into the second database. That is because executing the command attempts to add an already existing record again to the second database, which results in the fault sequence being executed. Therefore, an exception raised for duplicate entries and results in an entire transaction rollback.