JMS Scenarios

This section provides information on how to improve the performance of the following most common JMS use cases of WSO2 ESB.

ESB as a JMS consumer

In this scenario, WSO2 ESB listens to a JMS queue, consumes messages, and sends the messages to a HTTP back-end service.

You can improve the performance of this scenario by following the steps below.

If the queue gets filled up at a high rate, and the queue is long, you can improve the performance by increasing the number of concurrent consumers. Add the following parameters to the JMS listener configuration of the <ESB_HOME>/repository/conf/axis2/axis2.xml file to increasing the number of concurrent consumers:
```
<parameter name="transport.jms.ConcurrentConsumers" locked="false">50</parameter> 
<parameter name="transport.jms.MaxConcurrentConsumers" locked="false">50</parameter>
```
Add the following parameter to the JMS listener configuration of the <ESB_HOME>/repository/conf/axis2/axis2.xml file to enable JMS listener caching:
```
<parameter name="transport.jms.CacheLevel">consumer</parameter>
```
The possible values for the cache level are none, auto, connection, session and consumer. Out of the possible values, consumer is the highest level that provides maximum performance.

ESB as a JMS Producer

In this scenario, an ESB proxy service accepts messages from an HTTP client via HTTP and sends the messages to a JMS queue.

You can improve the performance of this scenario by following the steps below.

Add the following parameter to the JMS sender configuration of the <ESB_HOME>/repository/conf/axis2/axis2.xml file to enable JMS sender caching:
```
<parameter name="transport.jms.CacheLevel">producer</parameter>
```
The possible values for the cache level are none, auto, connection, session and producer. Out of the possible values, producer is the highest level that provides maximum performance.
Add the following parameter to the configuration to remove ClientApiNonBlocking when sending messages via JMS:
```
<property name="ClientApiNonBlocking" action="remove" scope="axis2"/>
```
Noe

By default, Axis2 spawns a new thread to handle each outgoing message. To change this behavior, you need to remove the ClientApiNonBlocking property from the message. Removal of this property is vital when queuing transports like JMS are involved.

ESB as Both a JMS Producer and Consumer

In this scenario, ESB listens to a JMS queue and consume messages, and also sends messages to a JMS queue.

To improve the performance of this scenario, you can follow the steps described in the scenario where the ESB acts as a JMS consumer as well the steps described in the scenario where the ESB acts as a JMS producer.