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<title>Administrative Methods</title>
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<link rel="up" href="databases.html" title="Chapter 7. Databases" />
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<p>Library Version 12.2.7.5</p>
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<th colspan="3" align="center">Administrative Methods</th>
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<td width="20%" align="left"><a accesskey="p" href="dbprops.html">Prev</a> </td>
<th width="60%" align="center">Chapter 7. Databases</th>
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<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="DBAdmin"></a>Administrative Methods</h2>
</div>
</div>
</div>
<p>
Both the <code class="classname">Environment</code> and
<code class="classname">Database</code> classes provide methods that are useful
for manipulating databases. These methods are:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="methodname">Database.getDatabaseName()</code>
</p>
<p>Returns the database's name.</p>
<a id="je_db3.1"></a>
<pre class="programlisting">String dbName = myDatabase.getDatabaseName();</pre>
<span>
</span>
</li>
<li>
<p>
<code class="methodname">Database.getEnvironment()</code>
</p>
<p>Returns the <code class="classname">Environment</code> that contains this database.</p>
<a id="je_db4"></a>
<pre class="programlisting">Environment theEnv = myDatabase.getEnvironment();</pre>
</li>
<li>
<p>
<code class="methodname">Database.preload()</code>
</p>
<p>Preloads the database into the in-memory cache. Optionally takes
a <code class="literal">long</code> that identifies the maximum number of bytes to load into the
cache. If this parameter is not supplied, the maximum memory usage
allowed by the evictor thread is used.
</p>
<a id="je_db6"></a>
<pre class="programlisting">myDatabase.preload(1048576l); // 1024*1024</pre>
</li>
<li>
<p>
<code class="methodname">Environment.getDatabaseNames()</code>
</p>
<p>Returns a list of Strings of all the databases contained by the
environment.</p>
<a id="je_db7"></a>
<pre class="programlisting">import java.util.List;
...
List myDbNames = myDbEnv.getDatabaseNames();
for(int i=0; i &lt; myDbNames.size(); i++) {
System.out.println("Database Name: " + (String)myDbNames.get(i));
}</pre>
</li>
<li>
<p>
<code class="methodname">Environment.removeDatabase()</code>
</p>
<p>Deletes the database. The database must be closed when you
perform this action on it.</p>
<a id="je_db8"></a>
<pre class="programlisting">String dbName = myDatabase.getDatabaseName();
myDatabase.close();
myDbEnv.removeDatabase(null, dbName);</pre>
</li>
<li>
<p>
<code class="methodname">Environment.renameDatabase()</code>
</p>
<p>Renames the database. The database must be closed when you
perform this action on it.</p>
<a id="je_db9"></a>
<pre class="programlisting">String oldName = myDatabase.getDatabaseName();
String newName = new String(oldName + ".new", "UTF-8");
myDatabase.close();
myDbEnv.renameDatabase(null, oldName, newName);</pre>
</li>
<li>
<p>
<code class="methodname">Environment.truncateDatabase()</code>
</p>
<p>
Deletes every record in the database and optionally returns the
number of records that were deleted. Note that it is much less
expensive to truncate a database without counting the number of
records deleted than it is to truncate and count.
</p>
<a id="je_db5"></a>
<pre class="programlisting">int numDiscarded =
myEnv.truncate(null, // txn handle
myDatabase.getDatabaseName(), // database name
true); // If true, then the
// number of records
// deleted are counted.
System.out.println("Discarded " + numDiscarded +
" records from database " +
myDatabase.getDatabaseName()); </pre>
</li>
</ul>
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