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<div class="subTitle">org.apache.hadoop.hbase.conf</div>
<h2 title="Class ConfigurationManager" class="title">Class ConfigurationManager</h2>
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<pre>@InterfaceAudience.Private
@InterfaceStability.Evolving
public class <a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.64">ConfigurationManager</a>
extends <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></pre>
<div class="block">Maintains the set of all the classes which would like to get notified when the Configuration is
reloaded from the disk in the Online Configuration Change mechanism, which lets you update
certain configuration properties on-the-fly, without having to restart the cluster.
<p>
If a class has configuration properties which you would like to be able to change on-the-fly, do
the following:
<ol>
<li>Implement the <a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf"><code>ConfigurationObserver</code></a> interface. This would require you to implement
the <a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html#onConfigurationChange-org.apache.hadoop.conf.Configuration-"><code>ConfigurationObserver.onConfigurationChange(Configuration)</code></a> method. This is a callback
that is used to notify your class' instance that the configuration has changed. In this method,
you need to check if the new values for the properties that are of interest to your class are
different from the cached values. If yes, update them. <br />
However, be careful with this. Certain properties might be trivially mutable online, but others
might not. Two properties might be trivially mutable by themselves, but not when changed
together. For example, if a method uses properties "a" and "b" to make some decision, and is
running in parallel when the notifyOnChange() method updates "a", but hasn't yet updated "b", it
might make a decision on the basis of a new value of "a", and an old value of "b". This might
introduce subtle bugs. This needs to be dealt on a case-by-case basis, and this class does not
provide any protection from such cases.</li>
<li>Register the appropriate instance of the class with the <a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html" title="class in org.apache.hadoop.hbase.conf"><code>ConfigurationManager</code></a>
instance, using the <a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#registerObserver-org.apache.hadoop.hbase.conf.ConfigurationObserver-"><code>registerObserver(ConfigurationObserver)</code></a> method.
Be careful not to do this in the constructor, as you might cause the 'this' reference to escape.
Use a factory method, or an initialize() method which is called after the construction of the
object.</li>
<li>Deregister the instance using the
<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#deregisterObserver-org.apache.hadoop.hbase.conf.ConfigurationObserver-"><code>deregisterObserver(ConfigurationObserver)</code></a> method when it is going
out of scope. In case you are not able to do that for any reason, it is still okay, since entries
for dead observers are automatically collected during GC. But nonetheless, it is still a good
practice to deregister your observer, whenever possible.</li>
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<td class="colFirst"><code>private <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Set.html?is-external=true" title="class or interface in java.util">Set</a>&lt;<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&gt;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#configurationObservers">configurationObservers</a></span></code>&nbsp;</td>
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<tr class="rowColor">
<td class="colFirst"><code>private static org.slf4j.Logger</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#LOG">LOG</a></span></code>&nbsp;</td>
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<td class="colOne"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#ConfigurationManager--">ConfigurationManager</a></span>()</code>&nbsp;</td>
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<td class="colFirst"><code>boolean</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#containsObserver-org.apache.hadoop.hbase.conf.ConfigurationObserver-">containsObserver</a></span>(<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&nbsp;observer)</code>
<div class="block">Returns true if contains the observer, for unit test only</div>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#deregisterObserver-org.apache.hadoop.hbase.conf.ConfigurationObserver-">deregisterObserver</a></span>(<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&nbsp;observer)</code>
<div class="block">Deregister an observer class</div>
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<td class="colFirst"><code>int</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#getNumObservers--">getNumObservers</a></span>()</code>
<div class="block">Returns the number of observers.</div>
</td>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#notifyAllObservers-org.apache.hadoop.conf.Configuration-">notifyAllObservers</a></span>(org.apache.hadoop.conf.Configuration&nbsp;conf)</code>
<div class="block">The conf object has been repopulated from disk, and we have to notify all the observers that
are expressed interest to do that.</div>
</td>
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<tr id="i4" class="altColor">
<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationManager.html#registerObserver-org.apache.hadoop.hbase.conf.ConfigurationObserver-">registerObserver</a></span>(<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&nbsp;observer)</code>
<div class="block">Register an observer class</div>
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<pre>private static final&nbsp;org.slf4j.Logger <a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.65">LOG</a></pre>
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<pre>private final&nbsp;<a href="https://docs.oracle.com/javase/8/docs/api/java/util/Set.html?is-external=true" title="class or interface in java.util">Set</a>&lt;<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&gt; <a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.71">configurationObservers</a></pre>
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<pre>public&nbsp;<a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.64">ConfigurationManager</a>()</pre>
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<pre>public&nbsp;void&nbsp;<a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.78">registerObserver</a>(<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&nbsp;observer)</pre>
<div class="block">Register an observer class</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>observer</code> - observer to be registered.</dd>
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<pre>public&nbsp;void&nbsp;<a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.91">deregisterObserver</a>(<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&nbsp;observer)</pre>
<div class="block">Deregister an observer class</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>observer</code> - to be deregistered.</dd>
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<pre>public&nbsp;void&nbsp;<a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.104">notifyAllObservers</a>(org.apache.hadoop.conf.Configuration&nbsp;conf)</pre>
<div class="block">The conf object has been repopulated from disk, and we have to notify all the observers that
are expressed interest to do that.</div>
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<pre>public&nbsp;int&nbsp;<a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.121">getNumObservers</a>()</pre>
<div class="block">Returns the number of observers.</div>
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<pre>public&nbsp;boolean&nbsp;<a href="../../../../../src-html/org/apache/hadoop/hbase/conf/ConfigurationManager.html#line.128">containsObserver</a>(<a href="../../../../../org/apache/hadoop/hbase/conf/ConfigurationObserver.html" title="interface in org.apache.hadoop.hbase.conf">ConfigurationObserver</a>&nbsp;observer)</pre>
<div class="block">Returns true if contains the observer, for unit test only</div>
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