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 esbdband 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.

In the master-datasources.xml file located in the <ESB_HOME>/repository/conf/datasources directory, create datasource declarations for the distributed databases, 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>

To build the sample

Start the ESB server and log into the Management Console. Click the Main tab on the Management Console, go to Manage -> Service Bus and then click Source View. Next, copy and paste the above synapse configuration to the source view.
Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.
Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services.

Infor

WSO2 ESB comes with a default JTA transaction manager (Atomikos), which allows you to run distributed transactions without deploying the ESB on an external application server.

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.