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Posted to commits@qpid.apache.org by kg...@apache.org on 2011/10/05 22:35:21 UTC
svn commit: r1179425 - in /qpid/branches/qpid-3346/qpid/doc/book/src:
AMQP-Messaging-Broker-CPP-Book.xml AMQP-Messaging-Broker-CPP.xml
Using-message-groups.xml
Author: kgiusti
Date: Wed Oct 5 20:35:21 2011
New Revision: 1179425
URL: http://svn.apache.org/viewvc?rev=1179425&view=rev
Log:
QPID-3346: add documentation
Added:
qpid/branches/qpid-3346/qpid/doc/book/src/Using-message-groups.xml
Modified:
qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP-Book.xml
qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP.xml
Modified: qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP-Book.xml
URL: http://svn.apache.org/viewvc/qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP-Book.xml?rev=1179425&r1=1179424&r2=1179425&view=diff
==============================================================================
--- qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP-Book.xml (original)
+++ qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP-Book.xml Wed Oct 5 20:35:21 2011
@@ -59,6 +59,7 @@
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="producer-flow-control.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="AMQP-Compatibility.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="Qpid-Interoperability-Documentation.xml"/>
+ <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="Using-message-groups.xml"/>
</chapter>
Modified: qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP.xml
URL: http://svn.apache.org/viewvc/qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP.xml?rev=1179425&r1=1179424&r2=1179425&view=diff
==============================================================================
--- qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP.xml (original)
+++ qpid/branches/qpid-3346/qpid/doc/book/src/AMQP-Messaging-Broker-CPP.xml Wed Oct 5 20:35:21 2011
@@ -52,6 +52,7 @@
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="Starting-a-cluster.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="ACL.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="producer-flow-control.xml"/>
+ <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="Using-message-groups.xml"/>
</chapter>
Added: qpid/branches/qpid-3346/qpid/doc/book/src/Using-message-groups.xml
URL: http://svn.apache.org/viewvc/qpid/branches/qpid-3346/qpid/doc/book/src/Using-message-groups.xml?rev=1179425&view=auto
==============================================================================
--- qpid/branches/qpid-3346/qpid/doc/book/src/Using-message-groups.xml (added)
+++ qpid/branches/qpid-3346/qpid/doc/book/src/Using-message-groups.xml Wed Oct 5 20:35:21 2011
@@ -0,0 +1,236 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements. See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership. The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing,
+ software distributed under the License is distributed on an
+ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ KIND, either express or implied. See the License for the
+ specific language governing permissions and limitations
+ under the License.
+
+-->
+
+<section id="Using-message-groups">
+ <title>
+ Using Message Groups
+ </title>
+
+ <section role="h2" id="usingmessagegroups-Overview">
+ <title>
+ Overview
+ </title>
+ <para>
+ The broker allows messaging applications to classify a set of related messages as
+ belonging to a group. This allows a message producer to indicate to the consumer
+ that a group of messages should be considered a single logical operation with
+ respect to the application.
+ </para>
+ <para>
+ The broker can use this group identification to enforce policies controlling how
+ messages from a given group can be distributed to consumers. For instance, the
+ broker can be configured to guarantee all the messages from a particular group are
+ processed in order across multiple consumers.
+ </para>
+ <para>
+ For example, assume we have a shopping application that manages items in a virtual
+ shopping cart. A user may add an item to their shopping cart, then change their
+ mind and remove it. If the application sends an <emphasis>add</emphasis> message to the broker,
+ immediately followed by a <emphasis>remove</emphasis> message, they will be queued in the proper
+ order - <emphasis>add</emphasis>, followed by <emphasis>remove</emphasis>.
+ </para>
+ <para>
+ However, if there are multiple consumers, it is possible that once a consumer
+ acquires the <emphasis>add</emphasis> message, a different consumer may acquire the
+ <emphasis>remove</emphasis> message. This allows both messages to be processed in parallel,
+ which could result in a "race" where the <emphasis>remove</emphasis> operation is incorrectly
+ performed before the <emphasis>add</emphasis> operation.
+ </para>
+ </section>
+ <!--h2-->
+ <section role="h2" id="usingmessagegroups-GroupingMessages">
+ <title>
+ Grouping Messages
+ </title>
+ <para>
+ In order to group messages, the application would designate a particular
+ application header as containing a message's <emphasis>group identifier</emphasis>. The group
+ identifier stored in that header field would be a string value set by the message
+ producer. Messages from the same group would have the same group identifier
+ value. The key that identifies the header must also be known to the message
+ consumers. This allows the consumers to determine a message's assigned group.
+ </para>
+ <para>
+ The header that is used to hold the group identifier, as well as the values used
+ as group identifiers, are totally under control of the application.
+ </para>
+ </section>
+ <section role="h2" id="usingmessagegroups-BrokerRole">
+ <title>
+ The Role of the Broker
+ </title>
+ <para>
+ The broker will apply the following processing on each grouped message:
+ <itemizedlist>
+ <listitem>Enqueue a received message on the destination queue.</listitem>
+ <listitem>Determine the message's group by examining the message's group identifier header.</listitem>
+ <listitem>Enforce <emphasis>consumption ordering</emphasis> among messages belonging to the same group.</listitem>
+ </itemizedlist>
+ <emphasis>Consumption ordering</emphasis> means that the broker will not allow outstanding
+ unacknowledged messages to <emphasis>more than one consumer for a given group</emphasis>.
+ </para>
+ <para>
+ This means that only one consumer can be processing messages from a particular
+ group at a given time. When the consumer acknowledges all of its acquired
+ messages, then the broker <emphasis>may</emphasis> pass the next message from that group to
+ another consumer.
+ </para>
+ <para>
+ Specifically, for any given group, the broker allows only the first N messages in
+ the group to be available for delivery to a particular consumer. The value of N
+ would be determined by the selected consumer's configured prefetch capacity. The
+ broker blocks access to the remaining messages in that group by any other
+ consumer. Once the selected consumer has acknowledged that first set of delivered
+ messages, the broker allows the next messages in the group to be available for
+ delivery. The next set of messages may be delivered to a different consumer.
+ </para>
+ <para>
+ Note well that distinct message groups would not block each other from delivery.
+ For example, assume a queue contains messages from two different message groups -
+ say group "A" and group "B" - and they are enqueued such that "A"'s messages are
+ in front of "B". If the first message of group "A" is in the process of being
+ consumed by a client, then the remaining "A" messages are blocked, but the
+ messages of the "B" group are available for consumption by other consumers - even
+ though it is "behind" group "A" in the queue.
+ </para>
+ </section>
+ <section role="h2" id="usingmessagegroups-ConsumerGuide">
+ <title>
+ Well Behaved Consumers
+ </title>
+ <para>
+ In order to guarantee the ordering policy, the consuming application has to ensure
+ that it has completely processed the data in a received message before accepting
+ that message, as described in Section 2.6.2. Transfer of Responsibility, of the
+ AMQP-0.10 specification.
+ </para>
+ <para>
+ The term <emphasis>processed</emphasis> means that the application has finished updating all
+ state related to the message that has been received.
+ </para>
+ <note>
+ <title>Be Advised</title>
+ <para>
+ It is possible for a consumer to affect the ordering of grouped messages even
+ when the broker is enforcing consumption order. This can be done by selectively
+ acknowledging and releasing messages from the same group.
+ </para>
+ <para>
+ Assume a consumer has received two messages from group "A", "A-1" and "A-2", in
+ that order. If the consumer releases "A-1" then acknowledges "A-2", "A-1" will
+ be put back onto the queue and "A-2" will be removed from the queue. This
+ allows another consumer to acquire and process "A-1" <emphasis>after</emphasis> "A-2" has been
+ processed.
+ </para>
+ <para>
+ Under some application-defined circumstances, this may be acceptable behavior.
+ However, if order must be preserved, the client should either release <emphasis>all</emphasis>
+ currently held messages, or discard the target message using reject.
+ </para>
+ </note>
+ </section>
+ <!--h2-->
+ <section role="h2" id="usingmessagegroups-BrokerConfig">
+ <title>
+ Broker Configuration
+ </title>
+ <para>
+ In order for the broker to determine a message's group, the key for the header
+ that contains the group identifier must be provided to the broker via
+ configuration. This is done on a per-queue basis, when the queue is first
+ configured.
+ </para>
+ <para>
+ This means that message group classification is determined by the message's destination
+ queue.
+ </para>
+ <para>
+ Specifically, the queue "holds" the header key that is used to find the message's
+ group identifier. All messages arriving at the queue are expected to use the same
+ header key for holding the identifer. Once the message is enqueued, the broker
+ looks up the group identifier in the message's header, and classifies the message
+ by its group.
+ </para>
+ <para>
+ Message group support can be enabled on a queue using the
+ <command>qpid-config</command> command line tool. The following options should be
+ provided when adding a new queue:
+ <programlisting>
+ --group-header=<replaceable>header-name</replaceable> Enable message group support for this queue. Specify name of application header that holds the group identifier.
+ --shared-groups Enforce ordered message group consumption across multiple consumers.
+ </programlisting>
+ </para>
+ <para>
+ Message group support may also be specified in the
+ <command>queue.declare</command> method via the <command>arguments</command>
+ parameter map, or using the messaging address syntax. The following keys must be
+ provided in the arguments map to enable message group support on a queue:
+ </para>
+ <table>
+ <title>Queue Declare/Addres Syntax Message Group Configuration Arguments</title>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Key</entry>
+ <entry>Value</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>qpid.group_header_key</entry>
+ <entry>string - key for message header that holds the group identifier value</entry>
+ </row>
+ <row>
+ <entry>qpid.shared_msg_group</entry>
+ <entry>1 - enforce ordering across multiple consumers</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ <para>
+ It is important to note that there is no need to provide the actual group
+ identifer values that will be used. The broker learns this values as messages are
+ recieved. Also, there is no practical limit - aside from resource limitations -
+ to the number of different groups that the broker can track at run time.
+ </para>
+ <note>
+ <title>Restrictions</title>
+ <para>
+ Message grouping is not supported on LVQ or Priority queues.
+ </para>
+ </note>
+ <section role="h3" id="usingmessagegroups-DefaultGroup">
+ <title>
+ Default Group
+ </title>
+ <para>
+ Should a message without a group identifier arrive at a queue configured for message grouping, the broker assigns the message to the default group. Therefore, all such "unidentified" messages are considered by the broker as part of the same group. The name of the default group is <command>"qpid.no-group"</command>. This default can be overridden by suppling a different value to the broker configuration item <command>"default-message-group"</command>:
+ <programlisting>
+ qpidd --default-msg-group "EMPTY-GROUP"
+ </programlisting>
+ </para>
+ </section>
+ </section>
+ </section>
+
+
+
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