activemq-artemis/docs/user-manual/en/last-value-queues.md

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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.
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 ?).
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());
Example
=======
See ? for an example which shows how last value queues are configured
and used with JMS.