Working with Transactions

A transaction is a set of operations executed as a single unit. It also can be defined as an agreement, which is carried out between separate entities or objects. A transaction can be considered as indivisible or atomic when it has the characteristic of either being completed in its entirety or not at all. During the event of a failure for a transaction update, atomic transaction type guarantees transaction integrity such that any partial updates are rolled back automatically.

Transactions have many different forms, such as financial transactions, database transactions etc.

From the ESB profile point of view, there are two types of transactions:

Distributed transactions

A distributed transaction is a transaction that updates data on two or more networked computer systems, such as two databases or a database and a message queue such as JMS. Implementing robust distributed applications is difficult because these applications are subject to multiple failures, including failure of the client, the server, and the network connection between the client and server. For distributed transactions, each computer has a local transaction manager. When a transaction works at multiple computers, the transaction managers interact with other transaction managers via either a superior or subordinate relationship. These relationships are relevant only for a particular transaction.

For an example that demonstrates how the transaction mediator can be used to manage distributed transactions, see Transaction Mediator Example.

Java Message Service (JMS) transactions

In addition to the transaction mediator, WSO2 Enterprise Integrator (WSO2 EI) also supports JMS transactions.

Note

In WSO2 EI, JMS transactions only work with either the Callout mediator or the Call mediator in blocking mode.

The JMS transport shipped with WSO2 EI supports both local and distributed JMS transactions. You can use local transactions to group messages received in a JMS queue. Local transactions are not supported for messages sent to a JMS queue.

This section describes:

JMS consumer transactions

Following sections describe the JMS consumer transactions.

JMS Local Transactions
JMS Distributed Transactions

JMS local transactions

A local transaction represents a unit of work on a single connection to a data source managed by a resource manager. In JMS, you can use the JMS API to get a transacted session and to call methods for commit or roll back for the relevant transaction objects. This is managed internally by a resource manager. There is no external transaction manager involved in the coordination of such transactions.

Let's explore a sample scenario that demonstrates how to handle a transaction using JMS in a situation where the back-end service is unreachable.

Sample scenario

A message is read from a JMS queue and is processed by a back-end service. In the successful scenario, the transaction will be committed and the request will be sent to the back end service. In the failure scenario, while executing a sequence, a failure occurs and WSO2 EI receives a fault. This cause the JMS transaction to roll back.

The sample scenario can be depicted as follows:

Prerequisites

Windows, Linux or Solaris operating systems with WSO2 EI installed. For instructions on downloading and installing WSO2 EI, see Installation Guide.
WSO2 ESB's JMS transport configured with the Broker profile of WSO2 EI. For instructions, see Configure with the Broker Profile.

Configuring the sample scenario

Configure the JMS local transaction by defining the following parameter in the <EI_HOME>/conf/axis2/axis2.xml file. By default the session is not transacted. In order to make it transacted, set the parameter to true.

<parameter name="transport.jms.SessionTransacted">true</parameter>

Once done, the JMS listener configuration for WSO2 MB in the axis2.xml file should be as follows:

<transportReceiver name="jms" class="org.apache.axis2.transport.jms.JMSListener">
       <parameter name="myTopicConnectionFactory" locked="false">
            <parameter name="java.naming.factory.initial" locked="false">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
            <parameter name="java.naming.provider.url" locked="false">repository/conf/jndi.properties</parameter>
            <parameter name="transport.jms.ConnectionFactoryJNDIName" locked="false">TopicConnectionFactory</parameter>
        	<parameter name="transport.jms.ConnectionFactoryType" locked="false">topic</parameter>
        	<parameter name="transport.jms.SessionTransacted">true</parameter>
       </parameter>
 
       <parameter name="myQueueConnectionFactory" locked="false">
           	<parameter name="java.naming.factory.initial" locked="false">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
           	<parameter name="java.naming.provider.url" locked="false">repository/conf/jndi.properties</parameter>
           	<parameter name="transport.jms.ConnectionFactoryJNDIName" locked="false">QueueConnectionFactory</parameter>
        	<parameter name="transport.jms.ConnectionFactoryType" locked="false">queue</parameter>
        	<parameter name="transport.jms.SessionTransacted">true</parameter>	
	   </parameter>
 
       <parameter name="default" locked="false">
           	<parameter name="java.naming.factory.initial" locked="false">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
           	<parameter name="java.naming.provider.url" locked="false">repository/conf/jndi.properties</parameter>
           	<parameter name="transport.jms.ConnectionFactoryJNDIName" locked="false">QueueConnectionFactory</parameter>
        	<parameter name="transport.jms.ConnectionFactoryType" locked="false">queue</parameter>
        	<parameter name="transport.jms.SessionTransacted">true</parameter>
		</parameter>
   </transportReceiver>

Copy and paste the following configuration into the Synapse configuration in <EI_HOME>/repository/deployment/server/synapse-configs/<node>/synapse.xml.

<definitions xmlns="http://ws.apache.org/ns/synapse">
   <proxy name="StockQuoteProxy" transports="jms" startOnLoad="true">
      <target>
         <inSequence>
            <property name="OUT_ONLY" value="true"/>
            <callout serviceURL="http://localhost:9000/services/SimpleStockQuoteService">
               <source type="envelope"/>
               <target key="placeOrder"/>
            </callout>
            <log level="custom">
               <property name="Transaction Action" value="Committed"/>
            </log>
         </inSequence>
         <faultSequence>
            <property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>
            <log level="custom">
               <property name="Transaction Action" value="Rollbacked"/>
            </log>
         </faultSequence>
      </target>
      <parameter name="transport.jms.ContentType">
         <rules>
            <jmsProperty>contentType</jmsProperty>
            <default>application/xml</default>
         </rules>
      </parameter>
   </proxy>
   <sequence name="fault">
      <log level="full">
         <property name="MESSAGE" value="Executing default &#34;fault&#34; sequence"/>
         <property name="ERROR_CODE" expression="get-property('ERROR_CODE')"/>
         <property name="ERROR_MESSAGE" expression="get-property('ERROR_MESSAGE')"/>
      </log>
      <drop/>
   </sequence>
   <sequence name="main">
      <log/>
      <drop/>
   </sequence>
</definitions>

According to the above configuration, a message will be read from the JMS queue and will be sent to the SimpleStockQuoteService running on the Axis2 back-end server. If a failure occurs, the transaction will roll back.

In the above configuration, the following property is set to true in the fault handler, in order to roll back the transaction when a failure occurs.

<property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>

If you are using a JMS Inbound endpoint for the transaction, set the scope of the SET_ROLLBACK_ONLY property to default as follows:

<property name="SET_ROLLBACK_ONLY" scope="default" type="STRING" value="true"/>

Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services.
Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.
You now have a running WSO2 EI instance, EI-Broker instance and a sample back-end service to simulate the sample scenario. Now let's execute the JMS client.

Due to the asynchronous behavior of the Send Mediator, you cannot you use it with a http/https endpoint, but you can use it in asynchronous use cases, for example with another JMS as endpoint.

Executing the sample scenario

To execute the JMS client

Run the following command from the <EI_HOME>/samples/axis2Client directory.

Currently, it is a known issue that this client does not work with the Broker profile of WSO2 EI. This will be fixed in future releases.
```
ant jmsclient -Djms_type=pox -Djms_dest=dynamicQueues/StockQuoteProxy -Djms_payload=MSFT
```
This will trigger a sample message to the JMS Server.

Testing the sample scenario

You can test the sample scenario as follows.

Successful scenario

If the message mediates successfully, you will view the output on the Axis2 server start-up console. Also, the ESB debug log will display an INFO message indicating that the transaction is committed.

Failure scenario

Stop the sample Axis2 Server and execute the JMS client once again to simulate the failure scenario. In this scenario, the ESB debug log will display an INFO message indicating that the transaction is rolled back.

JMS distributed transactions

WSO2 ESB also supports distributed JMS transactions. You can use the JMS transport with more than one distributed resource, for example, two remote database servers. An external transaction manager coordinates the transaction. Designing and using JMS distributed transactions is more complex than using local JMS transactions.

The transaction manager is the primary component of the distributed transaction infrastructure and distributed JMS transactions are managed by the XAResource enabled transaction manager in the Java 2 Platform, Enterprise Edition (J2EE) application server.

You will need to check if your message broker supports XA transactions prior to implementing distributed JMS transactions.

XA two-phase commit process

XA is a two-phase commit specification that is used in distributed transaction processing. Let's look at a sample scenario for JMS distributed transactions.

Sample Scenario

ESB listens to the message queue and sends that message to multiple queues. If something goes wrong in sending the message to one of those queues, the original message should be rolled back to the listening queue and none of the other queues should receive the message. Thus, the entire transaction should be rolled back.

Prerequisites

Windows, Linux or Solaris operating systems with WSO2 EI installed. For instructions on downloading and installing WSO2 EI, see Installation Guide.
WSO2 EI JMS transport configured with ActiveMQ. For instructions, see Configure with ActiveMQ.

Configuring the sample scenario

Create the JMSListenerProxy proxy service in WSO2 EI with the following configuration:

<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="JMSListenerProxy"
       transports="https http jms"
       startOnLoad="true">
   <description/>
   <target>
      <inSequence>
         <property name="OUT_ONLY" value="true"/>
         <log level="custom">
            <property name="MESSAGE_ID_A" expression="get-property('MessageID')"/>
         </log>
         <log level="custom">
            <property name="BEFORE" expression="$body"/>
         </log>
         <property name="MESSAGE_ID_B"
                   expression="get-property('MessageID')"
                   scope="operation"
                   type="STRING"/>
         <property name="failureResultProperty"
                   scope="default"
                   description="FailureResultProperty">
            <result xmlns="">failure</result>
         </property>
         <enrich>
            <source clone="true" xpath="$ctx:failureResultProperty"/>
            <target type="body"/>
         </enrich>
         <log level="custom">
            <property name="AFTER" expression="$body"/>
         </log>
         <property name="BEFORE1" value="ABCD" scope="axis2" type="STRING"/>
        <callout serviceURL="jms:/ActiveMQPublisher1?transport.jms.ConnectionFactoryJNDIName=XAConnectionFactory&amp;java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory&amp;java.naming.provider.url=tcp://localhost:61616&amp;transport.jms.DestinationType=queue;transport.jms.TransactionCommand=begin">
            <source type="envelope"/>
            <target xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
                    xmlns:s11="http://schemas.xmlsoap.org/soap/envelope/"
                    xpath="s11:Body/child::*[fn:position()=1] | s12:Body/child::*[fn:position()=1]"/>
         </callout>
         <callout serviceURL="jms:/ActiveMQPublisher2?transport.jms.ConnectionFactoryJNDIName=XAConnectionFactory&amp;java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory&amp;java.naming.provider.url=tcp://localhost:61616&amp;transport.jms.DestinationType=queue">
            <source type="envelope"/>
            <target xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
                    xmlns:s11="http://schemas.xmlsoap.org/soap/envelope/"
                    xpath="s11:Body/child::*[fn:position()=1] | s12:Body/child::*[fn:position()=1]"/>
         </callout>
         <callout serviceURL="jms:/ActiveMQPublisher3?transport.jms.ConnectionFactoryJNDIName=XAConnectionFactory&amp;java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory&amp;java.naming.provider.url=tcp://localhost:61616&amp;transport.jms.DestinationType=queue;transport.jms.TransactionCommand=end">
            <source type="envelope"/>
            <target xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
                    xmlns:s11="http://schemas.xmlsoap.org/soap/envelope/"
                    xpath="s11:Body/child::*[fn:position()=1] | s12:Body/child::*[fn:position()=1]"/>
         </callout>
         <drop/>
      </inSequence>
      <faultSequence>
         <log level="custom">
            <property name="Transaction Action" value="Rollbacked"/>
         </log>
         <callout serviceURL="jms:/ActiveMQPublisherFault?transport.jms.ConnectionFactoryJNDIName=XAConnectionFactory&amp;java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory&amp;java.naming.provider.url=tcp://localhost:61616&amp;transport.jms.DestinationType=queue;transport.jms.TransactionCommand=rollback">
            <source type="envelope"/>
            <target xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
                    xmlns:s11="http://schemas.xmlsoap.org/soap/envelope/"
                    xpath="s11:Body/child::*[fn:position()=1] | s12:Body/child::*[fn:position()=1]"/>
         </callout>
      </faultSequence>
   </target>
   <parameter name="transport.jms.ContentType">
      <rules>
         <jmsProperty>contentType</jmsProperty>
         <default>application/xml</default>
      </rules>
   </parameter>
   <parameter name="transport.jms.Destination">MyJMSQueue</parameter>
</proxy>

In the above configuration, WSO2 EI listens to a JMS queue named MyJMSQueue and consumes messages as well as sends messages to multiple JMS queues in a transactional manner.

To place a message into MyJMSQueue, execute the following command from <EI_HOME>/samples/axis2Client directory:
```
ant stockquote -Dmode=placeorder -Dtrpurl="jms:/MyJMSQueue?transport.jms.ConnectionFactoryJNDIName=QueueConnectionFactory&java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory&java.naming.provider.url=tcp://localhost:61616&transport.jms.ContentTypeProperty=Content-Type&transport.jms.DestinationType=queue"
```
You can see how WSO2 EI consumes messages from the queue named MyJMSQueue and sends the messages to multiple queues.
To check the rollback functionality provide an unreachable hostname to any destination queue and save the configurations. You should be able to observe WSO2 EI fault sequence getting invoked and failed message delivered to the destination configured in the fault sequence.

JMS publisher transactions

When you do not enable publisher transactions, the message publishing call to the Broker will not wait until the messages are persisted to the database. As a result, a successful HTTP response will be returned back to the caller even in a state where the database is disconnected. Hence, the message might actually be lost and not persisted in the Broker. Therefore, you can achieve guaranteed delivery by enabling publisher transactions.

The below is a sample scenario that demonstrates how to handle a publisher transaction using JMS.

Sample scenario

In this scenario, the client publishes JMS messages to the ESB profile of WSO2 EI. Then, the ESB profile publishes those messages to the JMS queue, which acts as the JMS endpoint. The sample scenario can be depicted as follows.

Prerequisites

Install WSO2 EI. For instructions, see Installation Guide.
Configure the JMS transport with the Broker Profile of WSO2 EI. For instructions, see Configure with the Broker Profile.

Configuring the sample scenario

Configure the JMS sender for the Broker profile in the JMS Sender section of the <EI_HOME>/conf/axis2/axis2_blocking_client.xml file as follows:

By default, the session is not transacted. Set the value of the sessionTransacted property to true, to make it transacted to publish transactions successfully.

<transportSender name="jms" class="org.apache.axis2.transport.jms.JMSSender">
    <parameter name="commonJmsSenderConnectionFactory" locked="false">
        <parameter locked="false" name="java.naming.factory.initial">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
        <parameter locked="false" name="java.naming.provider.url">conf/jndi.properties</parameter>
        <parameter locked="false" name="transport.jms.ConnectionFactoryJNDIName">QueueConnectionFactory</parameter>
        <parameter locked="false" name="transport.jms.ConnectionFactoryType">queue</parameter>
        <parameter locked="false" name="transport.jms.SessionTransacted">true</parameter>
    </parameter>
    <parameter name="commonTopicPublisherConnectionFactory" locked="false">
        <parameter locked="false" name="java.naming.factory.initial">org.wso2.andes.jndi.PropertiesFileInitialContextFactory</parameter>
        <parameter locked="false" name="java.naming.provider.url">conf/jndi.properties</parameter>
        <parameter locked="false" name="transport.jms.ConnectionFactoryJNDIName">TopicConnectionFactory</parameter>
        <parameter locked="false" name="transport.jms.ConnectionFactoryType">topic</parameter>
        <parameter locked="false" name="transport.jms.SessionTransacted">true</parameter>
    </parameter>
</transportSender>

Create an XML file with the below Synapse configuration of a sample publisher Proxy Service, and place the file inside the <EI_HOME>/repository/deployment/server/synapse-configs/default/proxy-services/ directory.

<proxy name="SampleProxy" transports="http" startOnLoad="true" xmlns="http://ws.apache.org/ns/synapse">
   <description/>
   <target>
      <inSequence>
         <property name="OUT_ONLY" value="true"/>
         <property name="messageType" value="text/xml" scope="axis2" type="STRING"/>
         <property name="routingKey" value="example.MyTopic" type="STRING"/>
         <call blocking="true">
            <endpoint>
               <address uri="jms:/example.MyTopic?transport.jms.ConnectionFactory=commonTopicPublisherConnectionFactory"/>
            </endpoint>
         </call>
         <payloadFactory media-type="xml">
            <format>
               <serviceResponse xmlns="">
                  <returnCode>200</returnCode>
                  <returnDesc>Successful</returnDesc>
                  <returnData>
                     <data name="routingKey" type="xml">$1</data>
                  </returnData>
               </serviceResponse>
            </format>
            <args>
               <arg evaluator="xml" expression="$ctx:routingKey"/>
            </args>
         </payloadFactory>
         <property name="HTTP_SC" value="200" scope="axis2" type="STRING"/>
         <respond/>
      </inSequence>
      <outSequence/>
      <faultSequence>
         <property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>
         <payloadFactory media-type="xml">
            <format>
               <serviceResponse xmlns="">
                  <returnCode>500</returnCode>
                  <returnDesc>Failure</returnDesc>
                  <returnData>
                     <data name="routingKey" type="xml">$1</data>
                  </returnData>
               </serviceResponse>
            </format>
            <args>
               <arg evaluator="xml" expression="$ctx:routingKey"/>
            </args>
         </payloadFactory>
         <property name="HTTP_SC" value="500" scope="axis2" type="STRING"/>
         <log level="full"/>
         <respond/>
      </faultSequence>
   </target>
</proxy>

Executing the sample scenario

Use a JMS client such as Apache JMeter to execute this sample scenario.

Testing the sample scenario

When a message is successfully published, it returns an HTTP 200 response to the client (successful scenario). In a case where it fails to publish a message, it executes the fault sequence returning an HTTP 500 response to the client (failure scenario).