Chapter 27. Last-Value Queues

27.1. Configuring Last-Value Queues
27.2. Using Last-Value Property
27.3. Example

Last-Value queues are special queues which discard any messages when a newer message with the same value for a well-defined Last-Value property is put in the queue. In other words, a Last-Value queue only retains the last value.

A typical example for Last-Value queue is for stock prices, where you are only interested by the latest value for a particular stock.

27.1. Configuring Last-Value Queues

Last-value queues are defined in the address-setting configuration:

<address-setting match="jms.queue.lastValueQueue">
    <last-value-queue>true</last-value-queue>
</address-setting>

By default, last-value-queue is false. Address wildcards can be used to configure Last-Value queues for a set of addresses (see Chapter 13, Understanding the HornetQ Wildcard Syntax).

27.2. Using Last-Value Property

The property name used to identify the last value is "_HQ_LVQ_NAME" (or the constant Message.HDR_LAST_VALUE_NAME from the Core API).

For example, if two messages with the same value for the Last-Value property are sent to a Last-Value queue, only the latest message will be kept in the queue:

// send 1st message with Last-Value property set to STOCK_NAME
TextMessage message = 
  session.createTextMessage("1st message with Last-Value property set");
message.setStringProperty("_HQ_LVQ_NAME", "STOCK_NAME");
producer.send(message);

// send 2nd message with Last-Value property set to STOCK_NAME             
message = 
  session.createTextMessage("2nd message with Last-Value property set");
message.setStringProperty("_HQ_LVQ_NAME", "STOCK_NAME");
producer.send(message);
       
...
       
// only the 2nd message will be received: it is the latest with 
// the Last-Value property set
TextMessage messageReceived = (TextMessage)messageConsumer.receive(5000);
System.out.format("Received message: %s\n", messageReceived.getText());

27.3. Example

See Section 11.1.31, “Last-Value Queue” for an example which shows how last value queues are configured and used with JMS.