# 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 ""