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<div class="sub-title"><span class="package-label-in-type">Package</span>&nbsp;<a href="package-summary.html">org.apache.hadoop.hbase</a></div>
<h1 title="Class ZNodeClearer" class="title">Class ZNodeClearer</h1>
</div>
<div class="inheritance" title="Inheritance Tree"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">java.lang.Object</a>
<div class="inheritance">org.apache.hadoop.hbase.ZNodeClearer</div>
</div>
<section class="class-description" id="class-description">
<hr>
<div class="type-signature"><span class="annotations">@Private
</span><span class="modifiers">public final class </span><span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-52">ZNodeClearer</a></span>
<span class="extends-implements">extends <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">Object</a></span></div>
<div class="block"><p>
Contains a set of methods for the collaboration between the start/stop scripts and the servers.
It allows to delete immediately the znode when the master or the regions server crashes. The
region server / master writes a specific file when it starts / becomes main master. When they end
properly, they delete the file.
</p>
<p>
In the script, we check for the existence of these files when the program ends. If they still
exist we conclude that the server crashed, likely without deleting their znode. To have a faster
recovery we delete immediately the znode.
</p>
<p>
The strategy depends on the server type. For a region server we store the znode path in the file,
and use it to delete it. for a master, as the znode path constant whatever the server, we check
its content to make sure that the backup server is not now in charge.
</p></div>
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<div class="col-first even-row-color"><code>private static final org.slf4j.Logger</code></div>
<div class="col-second even-row-color"><code><a href="#LOG" class="member-name-link">LOG</a></code></div>
<div class="col-last even-row-color">&nbsp;</div>
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<div class="col-first even-row-color"><code>private </code></div>
<div class="col-constructor-name even-row-color"><code><a href="#%3Cinit%3E()" class="member-name-link">ZNodeClearer</a>()</code></div>
<div class="col-last even-row-color">&nbsp;</div>
</div>
</section>
</li>
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<h2>Method Summary</h2>
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<div class="col-first even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static boolean</code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#clear(org.apache.hadoop.conf.Configuration)" class="member-name-link">clear</a><wbr>(org.apache.hadoop.conf.Configuration&nbsp;conf)</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">Delete the master znode if its content (ServerName string) is the same as the one in the znode
file.</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static void</code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#deleteMyEphemeralNodeOnDisk()" class="member-name-link">deleteMyEphemeralNodeOnDisk</a>()</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">delete the znode file</div>
</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#getMyEphemeralNodeFileName()" class="member-name-link">getMyEphemeralNodeFileName</a>()</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">Get the name of the file used to store the znode contents</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#parseMasterServerName(java.lang.String)" class="member-name-link">parseMasterServerName</a><wbr>(<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a>&nbsp;rsZnodePath)</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">See HBASE-14861.</div>
</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#readMyEphemeralNodeOnDisk()" class="member-name-link">readMyEphemeralNodeOnDisk</a>()</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">read the content of znode file, expects a single line.</div>
</div>
<div class="col-first odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static void</code></div>
<div class="col-second odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#writeMyEphemeralNodeOnDisk(java.lang.String)" class="member-name-link">writeMyEphemeralNodeOnDisk</a><wbr>(<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a>&nbsp;fileContent)</code></div>
<div class="col-last odd-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">Logs the errors without failing on exception.</div>
</div>
</div>
</div>
</div>
<div class="inherited-list">
<h3 id="methods-inherited-from-class-java.lang.Object">Methods inherited from class&nbsp;java.lang.<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">Object</a></h3>
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<!-- ============ FIELD DETAIL =========== -->
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<h2>Field Details</h2>
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<li>
<section class="detail" id="LOG">
<h3>LOG</h3>
<div class="member-signature"><span class="modifiers">private static final</span>&nbsp;<span class="return-type">org.slf4j.Logger</span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-54">LOG</a></span></div>
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<h2>Constructor Details</h2>
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<section class="detail" id="&lt;init&gt;()">
<h3>ZNodeClearer</h3>
<div class="member-signature"><span class="modifiers">private</span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-56">ZNodeClearer</a></span>()</div>
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<h2>Method Details</h2>
<ul class="member-list">
<li>
<section class="detail" id="writeMyEphemeralNodeOnDisk(java.lang.String)">
<h3>writeMyEphemeralNodeOnDisk</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type">void</span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-62">writeMyEphemeralNodeOnDisk</a></span><wbr><span class="parameters">(<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a>&nbsp;fileContent)</span></div>
<div class="block">Logs the errors without failing on exception.</div>
</section>
</li>
<li>
<section class="detail" id="readMyEphemeralNodeOnDisk()">
<h3>readMyEphemeralNodeOnDisk</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-98">readMyEphemeralNodeOnDisk</a></span>()
throws <span class="exceptions"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/io/IOException.html" title="class or interface in java.io" class="external-link">IOException</a></span></div>
<div class="block">read the content of znode file, expects a single line.</div>
<dl class="notes">
<dt>Throws:</dt>
<dd><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/io/IOException.html" title="class or interface in java.io" class="external-link">IOException</a></code></dd>
</dl>
</section>
</li>
<li>
<section class="detail" id="getMyEphemeralNodeFileName()">
<h3>getMyEphemeralNodeFileName</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-117">getMyEphemeralNodeFileName</a></span>()</div>
<div class="block">Get the name of the file used to store the znode contents</div>
</section>
</li>
<li>
<section class="detail" id="deleteMyEphemeralNodeOnDisk()">
<h3>deleteMyEphemeralNodeOnDisk</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type">void</span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-124">deleteMyEphemeralNodeOnDisk</a></span>()</div>
<div class="block">delete the znode file</div>
</section>
</li>
<li>
<section class="detail" id="parseMasterServerName(java.lang.String)">
<h3>parseMasterServerName</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a></span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-139">parseMasterServerName</a></span><wbr><span class="parameters">(<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a>&nbsp;rsZnodePath)</span></div>
<div class="block">See HBASE-14861. We are extracting master ServerName from rsZnodePath example:
"/hbase/rs/server.example.com,16020,1448266496481"</div>
<dl class="notes">
<dt>Parameters:</dt>
<dd><code>rsZnodePath</code> - from HBASE_ZNODE_FILE</dd>
<dt>Returns:</dt>
<dd>String representation of ServerName or null if fails</dd>
</dl>
</section>
</li>
<li>
<section class="detail" id="clear(org.apache.hadoop.conf.Configuration)">
<h3>clear</h3>
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type">boolean</span>&nbsp;<span class="element-name"><a href="../../../../src-html/org/apache/hadoop/hbase/ZNodeClearer.html#line-156">clear</a></span><wbr><span class="parameters">(org.apache.hadoop.conf.Configuration&nbsp;conf)</span></div>
<div class="block">Delete the master znode if its content (ServerName string) is the same as the one in the znode
file. (env: HBASE_ZNODE_FILE). I case of master-rs colloaction we extract ServerName string
from rsZnode path.(HBASE-14861)</div>
<dl class="notes">
<dt>Returns:</dt>
<dd>true on successful deletion, false otherwise.</dd>
</dl>
</section>
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