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From build...@apache.org
Subject svn commit: r960958 - in /websites/production/activemq/content: cache/main.pageCache virtual-destinations.html
Date Thu, 06 Aug 2015 12:20:57 GMT
Author: buildbot
Date: Thu Aug  6 12:20:57 2015
New Revision: 960958

Log:
Production update by buildbot for activemq

Modified:
    websites/production/activemq/content/cache/main.pageCache
    websites/production/activemq/content/virtual-destinations.html

Modified: websites/production/activemq/content/cache/main.pageCache
==============================================================================
Binary files - no diff available.

Modified: websites/production/activemq/content/virtual-destinations.html
==============================================================================
--- websites/production/activemq/content/virtual-destinations.html (original)
+++ websites/production/activemq/content/virtual-destinations.html Thu Aug  6 12:20:57 2015
@@ -83,40 +83,7 @@
   <tbody>
         <tr>
         <td valign="top" width="100%">
-<div class="wiki-content maincontent"><p><em>Virtual Destinations</em>
allow us to create logical destinations that clients can use to produce and consume from but
which map onto one or more <em>physical destinations</em>. It allows us to provide
more flexible loosely coupled messaging configurations.</p>
-
-<h2 id="VirtualDestinations-VirtualTopics">Virtual Topics</h2>
-
-<p>The idea behind <em>publish subscribe</em> is a great one. Allow producers
to be decoupled from consumers so that they do not even know how many consumers are interested
in the messages they publish. The JMS specification defines support for durable topics however
they have limitations as we will describe...</p>
-
-<h3 id="VirtualDestinations-ThelimitationsofJMSdurabletopics">The limitations of JMS
durable topics</h3>
-
-<p>A JMS durable subscriber MessageConsumer is created with a unique JMS clientID and
durable subscriber name. To be JMS compliant only one JMS connection can be active at any
point in time for one JMS clientID, and only one consumer can be active for a clientID and
subscriber name. i.e., only <strong>one</strong> thread can be actively consuming
from a given logical topic subscriber. This means we cannot implement</p>
-
-<ul><li>load balancing of messages.</li><li>fast failover of the
subscriber if that one process running that one consumer thread dies.</li></ul>
-
-
-<p>Now <em>queue</em> semantics in JMS offer the ability to load balance
work across a number of consumers in a reliable way - allowing many threads, processes and
machines to be used to process messages. Then we have sophisticated sticky load balancing
techniques like <a shape="rect" href="message-groups.html">Message Groups</a>
to load balance and parallelise work while maintaining ordering.</p>
-
-<p>Another added benefit of having physical queues for each logical topic subscriber
is we can them monitor the queue depths via <a shape="rect" href="jmx.html">JMX</a>
to monitor system performance together with being able to browse these physical queues.</p>
-
-<h3 id="VirtualDestinations-VirtualTopicstotherescue">Virtual Topics to the rescue</h3>
-
-<p>The idea behind virtual topics is that producers send to a topic in the usual JMS
way. Consumers can continue to use the Topic semantics in the JMS specification. However if
the topic is virtual, consumer can consume from a physical queue for a logical topic subscription,
allowing many consumers to be running on many machines &amp; threads to load balance the
load.</p>
-
-<p>E.g., let's say we have a topic called <strong>VirtualTopic.Orders</strong>.
(Where the prefix VirtualTopic. indicates its a virtual topic). And we logically want to send
orders to systems A and B. Now with regular durable topics we'd create a JMS consumer for
clientID_A and "A" along with clientID_B and "B".</p>
-
-<p>With virtual topics we can just go right ahead and consume to queue <strong>Consumer.A.VirtualTopic.Orders</strong>
to be a consumer for system A or consume to <strong>Consumer.B.VirtualTopic.Orders</strong>
to be a consumer for system B.</p>
-
-<p>We can now have a pool of consumers for each system which then compete for messages
for systems A or B such that all the messages for system A are processed exactly once and
similarly for system B.</p>
-
-<h3 id="VirtualDestinations-Customizingtheout-of-the-boxdefaults">Customizing the out-of-the-box
defaults</h3>
-
-<p>The out-of-the-box defaults are described above. Namely that the only virtual topics
available must be within the <strong>VirtualTopic.&gt;</strong> namespace
and that the consumer queues are named <strong>Consumer.*.VirtualTopic.&gt;</strong>.</p>
-
-<p>You can configure this to use whatever naming convention you wish. The following
<a shape="rect" class="external-link" href="https://svn.apache.org/repos/asf/incubator/activemq/trunk/activemq-unit-tests/src/test/resources/org/apache/activemq/broker/virtual/global-virtual-topics.xml">example</a>
shows how to make all topics virtual topics. The example below is using the name <strong>&gt;</strong>
to indicate 'match all topics'. You could use this wildcard to apply different virtual topic
policies in different hierarchies.</p>
-
-<div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent
pdl">
+<div class="wiki-content maincontent"><p><em>Virtual Destinations</em>
allow us to create logical destinations that clients can use to produce and consume from but
which map onto one or more <em>physical destinations</em>. It allows us to provide
more flexible loosely coupled messaging configurations.</p><h2 id="VirtualDestinations-VirtualTopics">Virtual
Topics</h2><p>The idea behind <em>publish subscribe</em> is a great
one. Allow producers to be decoupled from consumers so that they do not even know how many
consumers are interested in the messages they publish. The JMS specification defines support
for durable topics however they have limitations as we will describe...</p><h3 id="VirtualDestinations-ThelimitationsofJMSdurabletopics">The
limitations of JMS durable topics</h3><p>A JMS durable subscriber MessageConsumer
is created with a unique JMS clientID and durable subscriber name. To be JMS compliant only
one JMS connection can be active at any point in time for one JMS clientI
 D, and only one consumer can be active for a clientID and subscriber name. i.e., only <strong>one</strong>
thread can be actively consuming from a given logical topic subscriber. This means we cannot
implement</p><ul><li>load balancing of messages.</li><li>fast
failover of the subscriber if that one process running that one consumer thread dies.</li></ul><p>Now
<em>queue</em> semantics in JMS offer the ability to load balance work across
a number of consumers in a reliable way - allowing many threads, processes and machines to
be used to process messages. Then we have sophisticated sticky load balancing techniques like
<a shape="rect" href="message-groups.html">Message Groups</a> to load balance
and parallelise work while maintaining ordering.</p><p>Another added benefit of
having physical queues for each logical topic subscriber is we can them monitor the queue
depths via <a shape="rect" href="jmx.html">JMX</a> to monitor system performance
together with being able to browse these 
 physical queues.</p><h3 id="VirtualDestinations-VirtualTopicstotherescue">Virtual
Topics to the rescue</h3><p>The idea behind virtual topics is that producers send
to a topic in the usual JMS way. Consumers can continue to use the Topic semantics in the
JMS specification. However if the topic is virtual, consumer can consume from a physical queue
for a logical topic subscription, allowing many consumers to be running on many machines &amp;
threads to load balance the load.</p><p>E.g., let's say we have a topic called
<strong>VirtualTopic.Orders</strong>. (Where the prefix VirtualTopic. indicates
its a virtual topic). And we logically want to send orders to systems A and B. Now with regular
durable topics we'd create a JMS consumer for clientID_A and "A" along with clientID_B and
"B".</p><p>With virtual topics we can just go right ahead and consume to queue
<strong>Consumer.A.VirtualTopic.Orders</strong> to be a consumer for system A
or consume to <strong>Consumer.B.VirtualTopic.Orde
 rs</strong> to be a consumer for system B.</p><p>We can now have a pool
of consumers for each system which then compete for messages for systems A or B such that
all the messages for system A are processed exactly once and similarly for system B.</p><h3
id="VirtualDestinations-Customizingtheout-of-the-boxdefaults">Customizing the out-of-the-box
defaults</h3><p>The out-of-the-box defaults are described above. Namely that the
only virtual topics available must be within the <strong>VirtualTopic.&gt;</strong>
namespace and that the consumer queues are named <strong>Consumer.*.VirtualTopic.&gt;</strong>.</p><p>You
can configure this to use whatever naming convention you wish. The following <a shape="rect"
class="external-link" href="https://svn.apache.org/repos/asf/incubator/activemq/trunk/activemq-unit-tests/src/test/resources/org/apache/activemq/broker/virtual/global-virtual-topics.xml">example</a>
shows how to make all topics virtual topics. The example below is using the name <stron
 g>&gt;</strong> to indicate 'match all topics'. You could use this wildcard
to apply different virtual topic policies in different hierarchies.</p><div class="code
panel pdl" style="border-width: 1px;"><div class="codeContent panelContent pdl">
 <script class="brush: xml; gutter: false; theme: Default" type="syntaxhighlighter"><![CDATA[
 &lt;beans 
   xmlns=&quot;http://www.springframework.org/schema/beans&quot; 
@@ -140,17 +107,7 @@
 
 &lt;/beans&gt;
 ]]></script>
-</div></div>
-
-<p>Note that making a topic virtual does add a small CPU overhead when sending messages
to the topic but it is fairly small. From version <strong>5.4</strong>, dispatch
from virtual topics to subscription queues can be <strong>selectorAware</strong>
such that only messages that match one of the existing subscribers are actually dispatched.
Using this option prevents the build up of unmatched messages when selectors are used by exclusive
consumers.</p>
-
-<h2 id="VirtualDestinations-CompositeDestinations">Composite Destinations</h2>
-
-<p>Composite Destinations allow for one-to-many relationships on individual destinations;
the main use case is for <em>composite queues</em>. For example when a message
is sent to queue A you may want to forward it also to queues B and C and topic D. Composite
destinations are then a mapping from a virtual destination to a collection of other physical
destinations. In this case the mapping is broker side and the client is unaware of the mapping
between the destinations. This is different from client side <a shape="rect" href="composite-destinations.html">Composite
Destinations</a> where the client uses a URL notation to specify the actual physical
destinations that a message must be sent to.</p>
-
-<p>The following <a shape="rect" class="external-link" href="http://svn.apache.org/repos/asf/incubator/activemq/trunk/activemq-unit-tests/src/test/resources/org/apache/activemq/broker/virtual/composite-queue.xml">example</a>
shows how to set up a <strong>&lt;compositeQueue/&gt;</strong> element
in the XML configuration so that when a message is sent to <code>MY.QUEUE</code>
then it is really forwarded to the physical queue <code>FOO</code> and the topic
<code>BAR</code>.</p>
-
-<div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent
pdl">
+</div></div>Note that making a topic virtual does add a small CPU overhead when
sending messages to the topic but it is fairly small.<div class="table-wrap"><table
class="confluenceTable"><tbody><tr><th colspan="1" rowspan="1" class="confluenceTh">Option</th><th
colspan="1" rowspan="1" class="confluenceTh">Default</th><th colspan="1" rowspan="1"
class="confluenceTh">Description</th></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd">selectorAware</td><td colspan="1" rowspan="1" class="confluenceTd">false</td><td
colspan="1" rowspan="1" class="confluenceTd">only messages that match one of the existing
subscribers are actually dispatched. Using this option prevents the build up of unmatched
messages when selectors are used by exclusive consumers</td></tr><tr><td
colspan="1" rowspan="1" class="confluenceTd">local</td><td colspan="1" rowspan="1"
class="confluenceTd">false</td><td colspan="1" rowspan="1" class="confluenceTd">when
true, don't fan out messages that were received over
  a network</td></tr><tr><td colspan="1" rowspan="1" class="confluenceTd">concurrentSend</td><td
colspan="1" rowspan="1" class="confluenceTd">false</td><td colspan="1" rowspan="1"
class="confluenceTd">when true, use an executor to fanout such that sends occur in parallel.
This allows the journal to batch writes which will reduce disk io (5.12)</td></tr></tbody></table></div><p>&#160;</p><h2
id="VirtualDestinations-CompositeDestinations">Composite Destinations</h2><p>Composite
Destinations allow for one-to-many relationships on individual destinations; the main use
case is for <em>composite queues</em>. For example when a message is sent to queue
A you may want to forward it also to queues B and C and topic D. Composite destinations are
then a mapping from a virtual destination to a collection of other physical destinations.
In this case the mapping is broker side and the client is unaware of the mapping between the
destinations. This is different from client side <a shape="rect" href
 ="composite-destinations.html">Composite Destinations</a> where the client uses
a URL notation to specify the actual physical destinations that a message must be sent to.</p><p>The
following <a shape="rect" class="external-link" href="http://svn.apache.org/repos/asf/incubator/activemq/trunk/activemq-unit-tests/src/test/resources/org/apache/activemq/broker/virtual/composite-queue.xml">example</a>
shows how to set up a <strong>&lt;compositeQueue/&gt;</strong> element
in the XML configuration so that when a message is sent to <code>MY.QUEUE</code>
then it is really forwarded to the physical queue <code>FOO</code> and the topic
<code>BAR</code>.</p><div class="code panel pdl" style="border-width:
1px;"><div class="codeContent panelContent pdl">
 <script class="brush: xml; gutter: false; theme: Default" type="syntaxhighlighter"><![CDATA[
 &lt;beans 
   xmlns=&quot;http://www.springframework.org/schema/beans&quot; 
@@ -179,33 +136,13 @@
 
 &lt;/beans&gt;
 ]]></script>
-</div></div>
-
-<p>By default, subscribers cannot consume messages directly from a composite queue
or topic - it is a logical construct only. Given the configuration above, subscribers can
only consume messages from <code>FOO</code> and <code>BAR</code>;
but not <code>MY.QUEUE</code>.</p>
-
-<p>This behaviour can be altered to implement use cases such as watching a queue by
sending the same messages to a notification topic (wire tapping), by setting the optionally
set <code>forwardOnly</code> attribute to false.</p>
-
-<div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent
pdl">
+</div></div>By default, subscribers cannot consume messages directly from a composite
queue or topic - it is a logical construct only. Given the configuration above, subscribers
can only consume messages from <code>FOO</code> and <code>BAR</code>;
but not <code>MY.QUEUE</code>.<p>This behaviour can be altered to implement
use cases such as watching a queue by sending the same messages to a notification topic (wire
tapping), by setting the optionally set <code>forwardOnly</code> attribute to
false.</p><div class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
 <pre class="brush: xml; gutter: false; theme: Default" style="font-size:12px;">&lt;compositeQueue
name="IncomingOrders" forwardOnly="false"&gt;
     &lt;forwardTo&gt;
         &lt;topic physicalName="Notifications" /&gt;
     &lt;/forwardTo&gt;
 &lt;/compositeQueue&gt;</pre>
-</div></div>
-
-<p>Messages sent to <code>IncomingOrders</code> will all be copied and
forwarded to <code>Notifications</code>, before being placed on the physical <code>IncomingOrders</code>
queue for consumption by subscribers.</p>
-
-<p>Where the <code>forwardOnly</code> attribute is not defined or is set
to <code>true</code>, there is no logical difference between a <code>compositeQueue</code>
and a <code>compositeTopic</code> - they can be used interchangeably. It is only
when a composite destination is made physical through the use of <code>forwardOnly</code>
that the choice of <code>compositeTopic</code>/<code>compositeQueue</code>
has an impact on behavior.</p>
-
-<h3 id="VirtualDestinations-Usingfiltereddestinations">Using filtered destinations</h3>
-
-<p>From Apache ActiveMQ <strong>4.2</strong> onwards you can now use selectors
to define virtual destinations.</p>
-
-<p>You may wish to create a virtual destination which forwards messages to multiple
destinations but applying a selector first to decide if the message really does have to go
to a particular destination.</p>
-
-<p>The following example shows how a message sent to the virtual destination <strong>MY.QUEUE</strong>
will be forwarded to <strong>FOO</strong> and <strong>BAR</strong>
if the selectors match</p>
-
-<div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent
pdl">
+</div></div><p>Messages sent to <code>IncomingOrders</code>
will all be copied and forwarded to <code>Notifications</code>, before being placed
on the physical <code>IncomingOrders</code> queue for consumption by subscribers.</p><p>Where
the <code>forwardOnly</code> attribute is not defined or is set to <code>true</code>,
there is no logical difference between a <code>compositeQueue</code> and a <code>compositeTopic</code>
- they can be used interchangeably. It is only when a composite destination is made physical
through the use of <code>forwardOnly</code> that the choice of <code>compositeTopic</code>/<code>compositeQueue</code>
has an impact on behavior.</p><h3 id="VirtualDestinations-Usingfiltereddestinations">Using
filtered destinations</h3><p>From Apache ActiveMQ <strong>4.2</strong>
onwards you can now use selectors to define virtual destinations.</p><p>You may
wish to create a virtual destination which forwards messages to multiple destinations but
applying a selector first 
 to decide if the message really does have to go to a particular destination.</p><p>The
following example shows how a message sent to the virtual destination <strong>MY.QUEUE</strong>
will be forwarded to <strong>FOO</strong> and <strong>BAR</strong>
if the selectors match</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
 <script class="brush: xml; gutter: false; theme: Default" type="syntaxhighlighter"><![CDATA[
 &lt;beans 
   xmlns=&quot;http://www.springframework.org/schema/beans&quot; 
@@ -234,18 +171,8 @@
 
 &lt;/beans&gt;
 ]]></script>
-</div></div>
-
-
-<h2 id="VirtualDestinations-AvoidingDuplicateMessageinaNetworkofBrokers">Avoiding Duplicate
Message in a Network of Brokers</h2>
-
-<p>You have to make sure that the messages sent to the <strong>Consumer.*.VirtualTopic.&gt;</strong>
destination are not forwarded when you're using both queue-based and non-queue based subscribers
to the virtual topic (that is, if you have normal topic subscribers to the virtual topic).
 If you use Virtual Topics in a network of brokers, it is likely you will get duplicate messages
if you use the default network configuration.  This is because a network node will not only
forward message sent to the virtual topic, but also the associated physical queues.  To fix
this, you should disable forwarding messages on the associated physical queues.  </p>
-
-<p>Here is an example of how to do that:</p>
-
-<div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent
pdl">
-<pre class="brush: xml; gutter: false; theme: Default" style="font-size:12px;">
-    &lt;networkConnectors&gt;
+</div></div><h2 id="VirtualDestinations-AvoidingDuplicateMessageinaNetworkofBrokers">Avoiding
Duplicate Message in a Network of Brokers</h2><p>You have to make sure that the
messages sent to the <strong>Consumer.*.VirtualTopic.&gt;</strong> destination
are not forwarded when you're using both queue-based and non-queue based subscribers to the
virtual topic (that is, if you have normal topic subscribers to the virtual topic). If you
use Virtual Topics in a network of brokers, it is likely you will get duplicate messages if
you use the default network configuration. This is because a network node will not only forward
message sent to the virtual topic, but also the associated physical queues. To fix this, you
should disable forwarding messages on the associated physical queues.</p><p>Here
is an example of how to do that:</p><div class="code panel pdl" style="border-width:
1px;"><div class="codeContent panelContent pdl">
+<pre class="brush: xml; gutter: false; theme: Default" style="font-size:12px;">   
&lt;networkConnectors&gt;
       &lt;networkConnector uri="static://(tcp://localhost:61617)"&gt;
       	&lt;excludedDestinations&gt;
    	  &lt;queue physicalName="Consumer.*.VirtualTopic.&gt;"/&gt;



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