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<em xmlns="http://www.w3.org/1999/xhtml" class="parameter"><code>Changes-Since</code></em> Parameter</h1><div id="navheader" align="right"><table class="navLinks"><tr><td><a id="showHideButton" onclick="showHideToc();" class="pointLeft" title="Hide TOC tree">Sidebar

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<a accesskey="n" class="navLinkNext" href="ch03s09.html">Next</a></td></tr></table></div></div><div id="content"><div class="section" title="Efficient Polling with the Changes-Since Parameter"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="d877e480"/>Efficient Polling with the

<em class="parameter"><code>Changes-Since</code></em> Parameter</h2></div></div></div><p> The ReST API allows you to poll for the status of

certain operations by performing a <span class="command"><strong>GET</strong></span> on various

elements. Rather than re-downloading and re-parsing the

full status at each polling interval, your ReST client may

use the <em class="parameter"><code>changes-since</code></em> parameter to

check for changes since a previous request. The

<em class="parameter"><code>changes-since</code></em> time is specified as

an <a class="link" href="http://en.wikipedia.org/wiki/ISO_8601" target="_top">ISO

8601</a> dateTime (2011-01-24T17:08Z). You may also

specify a date without a timestamp (2011-01-24), in this

case the UTC timezone will be assumed. If nothing has

changed since the <em class="parameter"><code>changes-since</code></em>

time, a <span class="returnvalue">304 (Not Modified)</span>

response will be returned. If data has changed, only the

items changed since the specified time will be returned in

the response. For example, performing a <span class="command"><strong>GET</strong></span> against

https://api.servers.openstack.org/v1.1/224532/servers?<em class="parameter"><code>changes-since</code></em>=2011-01-24T17:08Z

would list all servers that have changed since Mon, 24 Jan

2011 17:08:00 UTC. </p></div><script xmlns="" type="text/javascript" src="../common/main.js"></script><hr xmlns=""/><h2 xmlns="" class="userNotes">User Notes On This Page</h2><div xmlns="" id="disqus_thread"><script type="text/javascript">

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