1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Introduction — Kombu 2.1.0 documentation</title>
<link rel="stylesheet" href="../_static/celery.css" type="text/css" />
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: '../',
VERSION: '2.1.0',
COLLAPSE_INDEX: false,
FILE_SUFFIX: '.html',
HAS_SOURCE: true
};
</script>
<script type="text/javascript" src="../_static/jquery.js"></script>
<script type="text/javascript" src="../_static/underscore.js"></script>
<script type="text/javascript" src="../_static/doctools.js"></script>
<link rel="top" title="Kombu 2.1.0 documentation" href="../index.html" />
<link rel="up" title="User Guide" href="index.html" />
<link rel="next" title="Connections and transports" href="connections.html" />
<link rel="prev" title="User Guide" href="index.html" />
</head>
<body>
<div class="related">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="connections.html" title="Connections and transports"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="index.html" title="User Guide"
accesskey="P">previous</a> |</li>
<li><a href="../index.html">Kombu 2.1.0 documentation</a> »</li>
<li><a href="index.html" accesskey="U">User Guide</a> »</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body">
<div class="section" id="introduction">
<span id="guide-intro"></span><h1>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h1>
<div class="section" id="what-is-messaging">
<span id="intro-messaging"></span><h2>What is messaging?<a class="headerlink" href="#what-is-messaging" title="Permalink to this headline">¶</a></h2>
<p>In times long ago people didn’t have email.
They had the postal service, which with great courage would deliver mail
from hand to hand all over the globe. Soldiers deployed at wars far away could only
communicate with their families through the postal service, and
posting a letter would mean that the recipient wouldn’t actually
receive the letter until weeks or months, sometimes years later.</p>
<p>It’s hard to imagine this today when people are expected to be available
for phone calls every minute of the day.</p>
<p>So humans need to communicate with each other, this shouldn’t
be news to anyone, but why would applications?</p>
<p>One example is banks.
When you transfer money from one bank to another, your bank sends
a message to the banks messaging central. The messaging central
then record and coordinate the transaction. Banks
need to send and receive millions and millions of
messages every day, and losing a single message would mean either losing
your money (bad) or the banks money (very bad)</p>
<p>Another example is the stock exchanges, which also have a need
for very high message throughputs and have strict reliability
requirements.</p>
<p>Email is a great way for people to communicate. It is much faster
than using the postal service, but still using email as a means for
programs to communicate would be like the soldier above, waiting
for signs of life from his girlfriend back home.</p>
</div>
<div class="section" id="messaging-scenarios">
<span id="id1"></span><h2>Messaging Scenarios<a class="headerlink" href="#messaging-scenarios" title="Permalink to this headline">¶</a></h2>
<ul>
<li><p class="first">Request/Reply</p>
<p>The request/reply pattern works like the postal service example.
A message is addressed to a single recipient, with a return address
printed on the back. The recipient may or may not reply to the
message by sending it back to the original sender.</p>
<p>Request-Reply is achieved using <em>direct</em> exchanges.</p>
</li>
<li><p class="first">Broadcast</p>
<p>In a broadcast scenario a message is sent to all parties.
This could be none, one or many recipients.</p>
<p>Broadcast is achieved using <em>fanout</em> exchanges.</p>
</li>
<li><p class="first">Publish/Subscribe</p>
<p>In a publish/subscribe scenario producers publish messages
to topics, and consumers subscribe to the topics they are
interested in.</p>
<p>If no consumers subscribe to the topic, then the message
will not be delivered to anyone. If several consumers
subscribe to the topic, then the message will be delivered
to all of them.</p>
<p>Pub-sub is achieved using <em>topic</em> exchanges.</p>
</li>
</ul>
</div>
<div class="section" id="reliability">
<span id="messaging-reliability"></span><h2>Reliability<a class="headerlink" href="#reliability" title="Permalink to this headline">¶</a></h2>
<p>For some applications reliability is very important. Losing a message is
a critical situation that must never happen. For other applications
losing a message is fine, it can maybe recover in other ways,
or the message is resent anyway as periodic updates.</p>
<p>AMQP defines two built-in delivery modes:</p>
<ul>
<li><p class="first">persistent</p>
<blockquote>
<div><p>Messages are written to disk and survives a broker restart.</p>
</div></blockquote>
</li>
<li><p class="first">transient</p>
<blockquote>
<div><p>Messages may or may not be written to disk, as the broker sees fit
to optimize memory contents. The messages will not survive a broker
restart.</p>
</div></blockquote>
</li>
</ul>
<p>Transient messaging is by far the fastest way to send and receive messages,
so having persistent messages comes with a price, but for some
applications this is a necessary cost.</p>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar">
<div class="sphinxsidebarwrapper"><p class="logo"><a href="../index.html">
<img class="logo" width="128" height="128" src="http://cloud.github.com/downloads/ask/kombu/kombusmall.jpg" alt="Logo"/>
</a></p>
<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Introduction</a><ul>
<li><a class="reference internal" href="#what-is-messaging">What is messaging?</a></li>
<li><a class="reference internal" href="#messaging-scenarios">Messaging Scenarios</a></li>
<li><a class="reference internal" href="#reliability">Reliability</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="index.html"
title="previous chapter">User Guide</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="connections.html"
title="next chapter">Connections and transports</a></p>
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../_sources/userguide/introduction.txt"
rel="nofollow">Show Source</a></li>
</ul>
<div id="searchbox" style="display: none">
<h3>Quick search</h3>
<form class="search" action="../search.html" method="get">
<input type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
<p class="searchtip" style="font-size: 90%">
Enter search terms or a module, class or function name.
</p>
</div>
<script type="text/javascript">$('#searchbox').show(0);</script>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
>index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="connections.html" title="Connections and transports"
>next</a> |</li>
<li class="right" >
<a href="index.html" title="User Guide"
>previous</a> |</li>
<li><a href="../index.html">Kombu 2.1.0 documentation</a> »</li>
<li><a href="index.html" >User Guide</a> »</li>
</ul>
</div>
<div class="footer">
© Copyright 2009-2012, Ask Solem.
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.2.
</div>
</body>
</html>
|
