Last-Value Queues

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.

Configuration

Last-Value queues can be statically configured via the last-value boolean property:

<address name="foo.bar">
   <multicast>
      <queue name="orders1" last-value="true"/>
   </multicast>
</address>

Specified on creating a queue by using the CORE api specifying the parameter lastValue to true.

Or on auto-create when using the JMS Client by using address parameters when creating the destination used by the consumer.

Queue queue = session.createQueue("my.destination.name?last-value=true");
Topic topic = session.createTopic("my.destination.name?last-value=true");

Also the default for all queues under and address can be defaulted using the address-setting configuration:

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

By default, default-last-value-queue is false. Address wildcards can be used to configure Last-Value queues for a set of addresses (see here).

Note that address-setting last-value-queue config is deprecated, please use default-last-value-queue instead.

Last-Value Property

The property name used to identify the last value is "_AMQ_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("_AMQ_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("_AMQ_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());

Example

See the last-value queue example which shows how last value queues are configured and used with JMS.

results matching ""

    No results matching ""