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+ <h1>
+ <i class="fa fa-circle-o-notch fa-spin"></i>
+ <a href="." >Message Grouping</a>
+ </h1>
+</div>
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+
+ <h1 id="message-grouping">Message Grouping</h1>
+<p>Message groups are sets of messages that have the following
+characteristics:</p>
+<ul>
+<li><p>Messages in a message group share the same group id, i.e. they have
+same group identifier property (<code>JMSXGroupID</code> for JMS,
+<code>_AMQ_GROUP_ID</code> for Apache ActiveMQ Artemis Core API).</p>
+</li>
+<li><p>Messages in a message group are always consumed by the same
+consumer, even if there are many consumers on a queue. They pin all
+messages with the same group id to the same consumer. If that
+consumer closes another consumer is chosen and will receive all
+messages with the same group id.</p>
+</li>
+</ul>
+<p>Message groups are useful when you want all messages for a certain value
+of the property to be processed serially by the same consumer.</p>
+<p>An example might be orders for a certain stock. You may want orders for
+any particular stock to be processed serially by the same consumer. To
+do this you can create a pool of consumers (perhaps one for each stock,
+but less will work too), then set the stock name as the value of the
+_AMQ_GROUP_ID property.</p>
+<p>This will ensure that all messages for a particular stock will always be
+processed by the same consumer.</p>
+<blockquote>
+<p><strong>Note</strong></p>
+<p>Grouped messages can impact the concurrent processing of non-grouped
+messages due to the underlying FIFO semantics of a queue. For example,
+if there is a chunk of 100 grouped messages at the head of a queue
+followed by 1,000 non-grouped messages then all the grouped messages
+will need to be sent to the appropriate client (which is consuming
+those grouped messages serially) before any of the non-grouped
+messages can be consumed. The functional impact in this scenario is a
+temporary suspension of concurrent message processing while all the
+grouped messages are processed. This can be a performance bottleneck
+so keep it in mind when determining the size of your message groups,
+and consider whether or not you should isolate your grouped messages
+from your non-grouped messages.</p>
+</blockquote>
+<h2 id="using-core-api">Using Core API</h2>
+<p>The property name used to identify the message group is <code>"_AMQ_GROUP_ID"</code>
+(or the constant <code>MessageImpl.HDR_GROUP_ID</code>). Alternatively, you can set
+<code>autogroup</code> to true on the <code>SessionFactory</code> which will pick a random
+unique id.</p>
+<h2 id="using-jms">Using JMS</h2>
+<p>The property name used to identify the message group is <code>JMSXGroupID</code>.</p>
+<pre><code> // send 2 messages in the same group to ensure the same
+ // consumer will receive both
+ Message message = ...
+ message.setStringProperty("JMSXGroupID", "Group-0");
+ producer.send(message);
+
+ message = ...
+ message.setStringProperty("JMSXGroupID", "Group-0");
+ producer.send(message);
+</code></pre><p>Alternatively, you can set <code>autogroup</code> to true on the
+<code>ActiveMQConnectonFactory</code> which will pick a random unique id. This can
+also be set in the JNDI context environment, e.g. <code>jndi.properties</code>.
+Here's a simple example using the "ConnectionFactory" connection factory
+which is available in the context by default</p>
+<pre><code>java.naming.factory.initial=org.apache.activemq.artemis.jndi.ActiveMQInitialContextFactory
+connectionFactory.myConnectionFactory=tcp://localhost:61616?autoGroup=true
+</code></pre><p>Alternatively you can set the group id via the connection factory. All
+messages sent with producers created via this connection factory will
+set the <code>JMSXGroupID</code> to the specified value on all messages sent. This
+can also be set in the JNDI context environment, e.g. <code>jndi.properties</code>.
+Here's a simple example using the "ConnectionFactory" connection factory
+which is available in the context by default:</p>
+<pre><code>java.naming.factory.initial=org.apache.activemq.artemis.jndi.ActiveMQInitialContextFactory
+connectionFactory.myConnectionFactory=tcp://localhost:61616?roupID=Group-0
+</code></pre><h2 id="example">Example</h2>
+<p>See the [examples](examples.md} chapter for an example which shows how message groups are configured and used with JMS and via a connection factory.</p>
+<h2 id="clustered-grouping">Clustered Grouping</h2>
+<p>Using message groups in a cluster is a bit more complex. This is because
+messages with a particular group id can arrive on any node so each node
+needs to know about which group id's are bound to which consumer on
+which node. The consumer handling messages for a particular group id may
+be on a different node of the cluster, so each node needs to know this
+information so it can route the message correctly to the node which has
+that consumer.</p>
+<p>To solve this there is the notion of a grouping handler. Each node will
+have its own grouping handler and when a messages is sent with a group
+id assigned, the handlers will decide between them which route the
+message should take.</p>
+<p>There are 2 types of handlers; Local and Remote. Each cluster should
+choose 1 node to have a local grouping handler and all the other nodes
+should have remote handlers- it's the local handler that actually makes
+the decision as to what route should be used, all the other remote
+handlers converse with this. Here is a sample config for both types of
+handler, this should be configured in the <em>broker.xml</em>
+file.</p>
+<pre><code><grouping-handler name="my-grouping-handler">
+ <type>LOCAL</type>
+ <address>jms</address>
+ <timeout>5000</timeout>
+</grouping-handler>
+
+<grouping-handler name="my-grouping-handler">
+ <type>REMOTE</type>
+ <address>jms</address>
+ <timeout>5000</timeout>
+</grouping-handler>
+</code></pre><p>The <em>address</em> attribute refers to a <a href="#clusters.address">cluster connection and the address
+it uses</a>, refer to the clustering section on how to
+configure clusters. The <em>timeout</em> attribute referees to how long to wait
+for a decision to be made, an exception will be thrown during the send
+if this timeout is reached, this ensures that strict ordering is kept.</p>
+<p>The decision as to where a message should be routed to is initially
+proposed by the node that receives the message. The node will pick a
+suitable route as per the normal clustered routing conditions, i.e.
+round robin available queues, use a local queue first and choose a queue
+that has a consumer. If the proposal is accepted by the grouping
+handlers the node will route messages to this queue from that point on,
+if rejected an alternative route will be offered and the node will again
+route to that queue indefinitely. All other nodes will also route to the
+queue chosen at proposal time. Once the message arrives at the queue
+then normal single server message group semantics take over and the
+message is pinned to a consumer on that queue.</p>
+<p>You may have noticed that there is a single point of failure with the
+single local handler. If this node crashes then no decisions will be
+able to be made. Any messages sent will be not be delivered and an
+exception thrown. To avoid this happening Local Handlers can be
+replicated on another backup node. Simple create your back up node and
+configure it with the same Local handler.</p>
+<h2 id="clustered-grouping-best-practices">Clustered Grouping Best Practices</h2>
+<p>Some best practices should be followed when using clustered grouping:</p>
+<ol>
+<li><p>Make sure your consumers are distributed evenly across the different
+nodes if possible. This is only an issue if you are creating and
+closing consumers regularly. Since messages are always routed to the
+same queue once pinned, removing a consumer from this queue may
+leave it with no consumers meaning the queue will just keep
+receiving the messages. Avoid closing consumers or make sure that
+you always have plenty of consumers, i.e., if you have 3 nodes have
+3 consumers.</p>
+</li>
+<li><p>Use durable queues if possible. If queues are removed once a group
+is bound to it, then it is possible that other nodes may still try
+to route messages to it. This can be avoided by making sure that the
+queue is deleted by the session that is sending the messages. This
+means that when the next message is sent it is sent to the node
+where the queue was deleted meaning a new proposal can successfully
+take place. Alternatively you could just start using a different
+group id.</p>
+</li>
+<li><p>Always make sure that the node that has the Local Grouping Handler
+is replicated. These means that on failover grouping will still
+occur.</p>
+</li>
+<li><p>In case you are using group-timeouts, the remote node should have a
+smaller group-timeout with at least half of the value on the main
+coordinator. This is because this will determine how often the
+last-time-use value should be updated with a round trip for a
+request to the group between the nodes.</p>
+</li>
+</ol>
+<h2 id="clustered-grouping-example">Clustered Grouping Example</h2>
+<p>See the <a href="examples.html">examples</a> chapter for an example of how to configure message groups with a ActiveMQ Artemis Cluster.</p>
+
+
+ </section>
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Added: websites/production/activemq/content/artemis/docs/latest/messaging-concepts.html
==============================================================================
--- websites/production/activemq/content/artemis/docs/latest/messaging-concepts.html (added)
+++ websites/production/activemq/content/artemis/docs/latest/messaging-concepts.html Thu Sep 14 19:48:11 2017
@@ -0,0 +1,1296 @@
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+ <li class="chapter " data-level="1.15" data-path="wildcard-routing.html">
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+ <a href="wildcard-routing.html">
+
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+ Routing Messages With Wild Cards
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+ </li>
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+ <li class="chapter " data-level="1.16" data-path="wildcard-syntax.html">
+
+ <a href="wildcard-syntax.html">
+
+
+ Understanding the Apache ActiveMQ Artemis Wildcard Syntax
+
+ </a>
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+ Filter Expressions
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+ <a href="configuring-transports.html">
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+ Configuring Transports
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+ <a href="config-reload.html">
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+ Configuration Reload
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+ </li>
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+ <li class="chapter " data-level="1.21" data-path="connection-ttl.html">
+
+ <a href="connection-ttl.html">
+
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+ Detecting Dead Connections
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+ <li class="chapter " data-level="1.22" data-path="slow-consumers.html">
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+ <a href="slow-consumers.html">
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+ Detecting Slow Consumers
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+ <a href="network-isolation.html">
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+ Avoiding Network Isolation
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+ <li class="chapter " data-level="1.24" data-path="critical-analysis.html">
+
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+ Detecting Broker Issues (Critical Analysis)
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+ <li class="chapter " data-level="1.25" data-path="transaction-config.html">
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+ Message Redelivery and Undelivered Messages
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+ Message Grouping
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+ <a href="." >Messaging Concepts</a>
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+ <h1 id="messaging-concepts">Messaging Concepts</h1>
+<p>Apache ActiveMQ Artemis is an asynchronous messaging system, an example of <a href="http://en.wikipedia.org/wiki/Message_oriented_middleware" target="_blank">Message
+Oriented
+Middleware</a> ,
+we'll just call them messaging systems in the remainder of this book.</p>
+<p>We'll first present a brief overview of what kind of things messaging
+systems do, where they're useful and the kind of concepts you'll hear
+about in the messaging world.</p>
+<p>If you're already familiar with what a messaging system is and what it's
+capable of, then you can skip this chapter.</p>
+<h2 id="messaging-concepts">Messaging Concepts</h2>
+<p>Messaging systems allow you to loosely couple heterogeneous systems
+together, whilst typically providing reliability, transactions and many
+other features.</p>
+<p>Unlike systems based on a <a href="http://en.wikipedia.org/wiki/Remote_procedure_call" target="_blank">Remote Procedure
+Call</a> (RPC) pattern,
+messaging systems primarily use an asynchronous message passing pattern
+with no tight relationship between requests and responses. Most
+messaging systems also support a request-response mode but this is not a
+primary feature of messaging systems.</p>
+<p>Designing systems to be asynchronous from end-to-end allows you to
+really take advantage of your hardware resources, minimizing the amount
+of threads blocking on IO operations, and to use your network bandwidth
+to its full capacity. With an RPC approach you have to wait for a
+response for each request you make so are limited by the network round
+trip time, or <em>latency</em> of your network. With an asynchronous system you
+can pipeline flows of messages in different directions, so are limited
+by the network <em>bandwidth</em> not the latency. This typically allows you to
+create much higher performance applications.</p>
+<p>Messaging systems decouple the senders of messages from the consumers of
+messages. The senders and consumers of messages are completely
+independent and know nothing of each other. This allows you to create
+flexible, loosely coupled systems.</p>
+<p>Often, large enterprises use a messaging system to implement a message
+bus which loosely couples heterogeneous systems together. Message buses
+often form the core of an <a href="http://en.wikipedia.org/wiki/Enterprise_service_bus" target="_blank">Enterprise Service
+Bus</a>. (ESB). Using
+a message bus to de-couple disparate systems can allow the system to
+grow and adapt more easily. It also allows more flexibility to add new
+systems or retire old ones since they don't have brittle dependencies on
+each other.</p>
+<h2 id="messaging-styles">Messaging styles</h2>
+<p>Messaging systems normally support two main styles of asynchronous
+messaging: <a href="http://en.wikipedia.org/wiki/Message_queue" target="_blank">message queue</a>
+messaging (also known as <em>point-to-point messaging</em>) and <a href="http://en.wikipedia.org/wiki/Publish_subscribe" target="_blank">publish
+subscribe</a> messaging.
+We'll summarise them briefly here:</p>
+<h3 id="the-message-queue-pattern">The Message Queue Pattern</h3>
+<p>With this type of messaging you send a message to a queue. The message
+is then typically persisted to provide a guarantee of delivery, then
+some time later the messaging system delivers the message to a consumer.
+The consumer then processes the message and when it is done, it
+acknowledges the message. Once the message is acknowledged it disappears
+from the queue and is not available to be delivered again. If the system
+crashes before the messaging server receives an acknowledgement from the
+consumer, then on recovery, the message will be available to be
+delivered to a consumer again.</p>
+<p>With point-to-point messaging, there can be many consumers on the queue
+but a particular message will only ever be consumed by a maximum of one
+of them. Senders (also known as <em>producers</em>) to the queue are completely
+decoupled from receivers (also known as <em>consumers</em>) of the queue - they
+do not know of each other's existence.</p>
+<p>A classic example of point to point messaging would be an order queue in
+a company's book ordering system. Each order is represented as a message
+which is sent to the order queue. Let's imagine there are many front end
+ordering systems which send orders to the order queue. When a message
+arrives on the queue it is persisted - this ensures that if the server
+crashes the order is not lost. Let's also imagine there are many
+consumers on the order queue - each representing an instance of an order
+processing component - these can be on different physical machines but
+consuming from the same queue. The messaging system delivers each
+message to one and only one of the ordering processing components.
+Different messages can be processed by different order processors, but a
+single order is only processed by one order processor - this ensures
+orders aren't processed twice.</p>
+<p>As an order processor receives a message, it fulfills the order, sends
+order information to the warehouse system and then updates the order
+database with the order details. Once it's done that it acknowledges the
+message to tell the server that the order has been processed and can be
+forgotten about. Often the send to the warehouse system, update in
+database and acknowledgement will be completed in a single transaction
+to ensure <a href="http://en.wikipedia.org/wiki/ACID" target="_blank">ACID</a> properties.</p>
+<h3 id="the-publish-subscribe-pattern">The Publish-Subscribe Pattern</h3>
+<p>With publish-subscribe messaging many senders can send messages to an
+entity on the server, often called a <em>topic</em> (e.g. in the JMS world).</p>
+<p>There can be many <em>subscriptions</em> on a topic, a subscription is just
+another word for a consumer of a topic. Each subscription receives a
+<em>copy</em> of <em>each</em> message sent to the topic. This differs from the
+message queue pattern where each message is only consumed by a single
+consumer.</p>
+<p>Subscriptions can optionally be <em>durable</em> which means they retain a copy
+of each message sent to the topic until the subscriber consumes them -
+even if the server crashes or is restarted in between. Non-durable
+subscriptions only last a maximum of the lifetime of the connection that
+created them.</p>
+<p>An example of publish-subscribe messaging would be a news feed. As news
+articles are created by different editors around the world they are sent
+to a news feed topic. There are many subscribers around the world who
+are interested in receiving news items - each one creates a subscription
+and the messaging system ensures that a copy of each news message is
+delivered to each subscription.</p>
+<h2 id="delivery-guarantees">Delivery guarantees</h2>
+<p>A key feature of most messaging systems is <em>reliable messaging</em>. With
+reliable messaging the server gives a guarantee that the message will be
+delivered once and only once to each consumer of a queue or each durable
+subscription of a topic, even in the event of system failure. This is
+crucial for many businesses; e.g. you don't want your orders fulfilled
+more than once or any of your orders to be lost.</p>
+<p>In other cases you may not care about a once and only once delivery
+guarantee and are happy to cope with duplicate deliveries or lost
+messages - an example of this might be transient stock price updates -
+which are quickly superseded by the next update on the same stock. The
+messaging system allows you to configure which delivery guarantees you
+require.</p>
+<h2 id="transactions">Transactions</h2>
+<p>Messaging systems typically support the sending and acknowledgement of
+multiple messages in a single local transaction. Apache ActiveMQ Artemis also supports
+the sending and acknowledgement of message as part of a large global
+transaction - using the Java mapping of XA: JTA.</p>
+<h2 id="durability">Durability</h2>
+<p>Messages are either durable or non durable. Durable messages will be
+persisted in permanent storage and will survive server failure or
+restart. Non durable messages will not survive server failure or
+restart. Examples of durable messages might be orders or trades, where
+they cannot be lost. An example of a non durable message might be a
+stock price update which is transitory and doesn't need to survive a
+restart.</p>
+<h2 id="messaging-apis-and-protocols">Messaging APIs and protocols</h2>
+<p>How do client applications interact with messaging systems in order to
+send and consume messages?</p>
+<p>Several messaging systems provide their own proprietary APIs with which
+the client communicates with the messaging system.</p>
+<p>There are also some standard ways of operating with messaging systems
+and some emerging standards in this space.</p>
+<p>Let's take a brief look at these:</p>
+<h3 id="java-message-service-jms">Java Message Service (JMS)</h3>
+<p><a href="http://en.wikipedia.org/wiki/Java_Message_Service" target="_blank">JMS</a> is part of
+Oracle's Java EE specification. It's a Java API that encapsulates both message
+queue and publish-subscribe messaging patterns. JMS is a lowest common
+denominator specification - i.e. it was created to encapsulate common
+functionality of the already existing messaging systems that were
+available at the time of its creation.</p>
+<p>JMS is a very popular API and is implemented by most messaging systems.
+JMS is only available to clients running Java.</p>
+<p>JMS does not define a standard wire format - it only defines a
+programmatic API so JMS clients and servers from different vendors
+cannot directly interoperate since each will use the vendor's own
+internal wire protocol.</p>
+<p>Apache ActiveMQ Artemis provides a fully compliant JMS 1.1 and JMS 2.0 API.</p>
+<h3 id="system-specific-apis">System specific APIs</h3>
+<p>Many systems provide their own programmatic API for which to interact
+with the messaging system. The advantage of this it allows the full set
+of system functionality to be exposed to the client application. API's
+like JMS are not normally rich enough to expose all the extra features
+that most messaging systems provide.</p>
+<p>Apache ActiveMQ Artemis provides its own core client API for clients to use if they
+wish to have access to functionality over and above that accessible via
+the JMS API.</p>
+<h3 id="restful-api">RESTful API</h3>
+<p><a href="http://en.wikipedia.org/wiki/Representational_State_Transfer" target="_blank">REST</a>
+approaches to messaging are showing a lot interest recently.</p>
+<p>It seems plausible that API standards for cloud computing may converge
+on a REST style set of interfaces and consequently a REST messaging
+approach is a very strong contender for becoming the de-facto method for
+messaging interoperability.</p>
+<p>With a REST approach messaging resources are manipulated as resources
+defined by a URI and typically using a simple set of operations on those
+resources, e.g. PUT, POST, GET etc. REST approaches to messaging often
+use HTTP as their underlying protocol.</p>
+<p>The advantage of a REST approach with HTTP is in its simplicity and the
+fact the internet is already tuned to deal with HTTP optimally.</p>
+<p>Please see <a href="rest.html">Rest Interface</a> for using Apache ActiveMQ Artemis's RESTful interface.</p>
+<h3 id="amqp">AMQP</h3>
+<p><a href="http://en.wikipedia.org/wiki/AMQP" target="_blank">AMQP</a> is a specification for
+interoperable messaging. It also defines a wire format, so any AMQP
+client can work with any messaging system that supports AMQP. AMQP
+clients are available in many different programming languages.</p>
+<p>Apache ActiveMQ Artemis implements the <a href="https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=amqp" target="_blank">AMQP
+1.0</a>
+specification. Any client that supports the 1.0 specification will be
+able to interact with Apache ActiveMQ Artemis.</p>
+<h3 id="mqtt">MQTT</h3>
+<p><a href="http://mqtt.org/" target="_blank">MQTT</a> is a lightweight connectivity protocol. It is designed
+to run in environments where device and networks are constrained. Out of the box
+Apache ActiveMQ Artemis supports version MQTT 3.1.1. Any client supporting this
+version of the protocol will work against Apache ActiveMQ Artemis.</p>
+<h3 id="stomp">STOMP</h3>
+<p><a href="http://stomp.github.io/" target="_blank">Stomp</a> is a very simple text protocol for
+interoperating with messaging systems. It defines a wire format, so
+theoretically any Stomp client can work with any messaging system that
+supports Stomp. Stomp clients are available in many different
+programming languages.</p>
+<p>Please see <a href="protocols-interoperability.html">Stomp</a> for using STOMP with Apache ActiveMQ Artemis.</p>
+<h3 id="openwire">OPENWIRE</h3>
+<p>ActiveMQ 5.x defines it's own wire Protocol "OPENWIRE". In order to support
+ActiveMQ 5.x clients, Apache ActiveMQ Artemis supports OPENWIRE. Any ActiveMQ 5.12.x
+or higher can be used with Apache ActiveMQ Artemis.</p>
+<h2 id="high-availability">High Availability</h2>
+<p>High Availability (HA) means that the system should remain operational
+after failure of one or more of the servers. The degree of support for
+HA varies between various messaging systems.</p>
+<p>Apache ActiveMQ Artemis provides automatic failover where your sessions are
+automatically reconnected to the backup server on event of live server
+failure.</p>
+<p>For more information on HA, please see <a href="ha.html">High Availability and Failover</a>.</p>
+<h2 id="clusters">Clusters</h2>
+<p>Many messaging systems allow you to create groups of messaging servers
+called <em>clusters</em>. Clusters allow the load of sending and consuming
+messages to be spread over many servers. This allows your system to
+scale horizontally by adding new servers to the cluster.</p>
+<p>Degrees of support for clusters varies between messaging systems, with
+some systems having fairly basic clusters with the cluster members being
+hardly aware of each other.</p>
+<p>Apache ActiveMQ Artemis provides very configurable state-of-the-art clustering model
+where messages can be intelligently load balanced between the servers in
+the cluster, according to the number of consumers on each node, and
+whether they are ready for messages.</p>
+<p>Apache ActiveMQ Artemis also has the ability to automatically redistribute messages
+between nodes of a cluster to prevent starvation on any particular node.</p>
+<p>For full details on clustering, please see <a href="clusters.html">Clusters</a>.</p>
+<h2 id="bridges-and-routing">Bridges and routing</h2>
+<p>Some messaging systems allow isolated clusters or single nodes to be
+bridged together, typically over unreliable connections like a wide area
+network (WAN), or the internet.</p>
+<p>A bridge normally consumes from a queue on one server and forwards
+messages to another queue on a different server. Bridges cope with
+unreliable connections, automatically reconnecting when the connections
+becomes available again.</p>
+<p>Apache ActiveMQ Artemis bridges can be configured with filter expressions to only
+forward certain messages, and transformation can also be hooked in.</p>
+<p>Apache ActiveMQ Artemis also allows routing between queues to be configured in server
+side configuration. This allows complex routing networks to be set up
+forwarding or copying messages from one destination to another, forming
+a global network of interconnected brokers.</p>
+<p>For more information please see <a href="core-bridges.html">Core Bridges</a> and <a href="diverts.html">Diverting and Splitting Message Flows</a>.</p>
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