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157 lines
6.4 KiB
HTML
157 lines
6.4 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Administrative Methods</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="databases.html" title="Chapter 7. Databases" />
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<link rel="prev" href="dbprops.html" title="Database Properties" />
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<link rel="next" href="dbUsage.html" title="Database Example" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Administrative Methods</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbprops.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 7. Databases</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbUsage.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="DBAdmin"></a>Administrative Methods</h2>
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</div>
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</div>
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</div>
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<p>
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Both the <code class="classname">Environment</code> and
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<code class="classname">Database</code> classes provide methods that are useful
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for manipulating databases. These methods are:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="methodname">Database.getDatabaseName()</code>
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</p>
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<p>Returns the database's name.</p>
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<a id="je_db3.1"></a>
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<pre class="programlisting">String dbName = myDatabase.getDatabaseName();</pre>
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<span>
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</span>
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</li>
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<li>
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<p>
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<code class="methodname">Database.getEnvironment()</code>
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</p>
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<p>Returns the <code class="classname">Environment</code> that contains this database.</p>
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<a id="je_db4"></a>
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<pre class="programlisting">Environment theEnv = myDatabase.getEnvironment();</pre>
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</li>
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<li>
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<p>
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<code class="methodname">Database.preload()</code>
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</p>
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<p>Preloads the database into the in-memory cache. Optionally takes
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a <code class="literal">long</code> that identifies the maximum number of bytes to load into the
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cache. If this parameter is not supplied, the maximum memory usage
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allowed by the evictor thread is used.
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</p>
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<a id="je_db6"></a>
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<pre class="programlisting">myDatabase.preload(1048576l); // 1024*1024</pre>
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</li>
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<li>
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<p>
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<code class="methodname">Environment.getDatabaseNames()</code>
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</p>
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<p>Returns a list of Strings of all the databases contained by the
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environment.</p>
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<a id="je_db7"></a>
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<pre class="programlisting">import java.util.List;
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...
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List myDbNames = myDbEnv.getDatabaseNames();
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for(int i=0; i < myDbNames.size(); i++) {
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System.out.println("Database Name: " + (String)myDbNames.get(i));
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}</pre>
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</li>
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<li>
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<p>
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<code class="methodname">Environment.removeDatabase()</code>
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</p>
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<p>Deletes the database. The database must be closed when you
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perform this action on it.</p>
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<a id="je_db8"></a>
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<pre class="programlisting">String dbName = myDatabase.getDatabaseName();
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myDatabase.close();
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myDbEnv.removeDatabase(null, dbName);</pre>
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</li>
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<li>
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<p>
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<code class="methodname">Environment.renameDatabase()</code>
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</p>
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<p>Renames the database. The database must be closed when you
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perform this action on it.</p>
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<a id="je_db9"></a>
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<pre class="programlisting">String oldName = myDatabase.getDatabaseName();
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String newName = new String(oldName + ".new", "UTF-8");
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myDatabase.close();
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myDbEnv.renameDatabase(null, oldName, newName);</pre>
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</li>
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<li>
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<p>
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<code class="methodname">Environment.truncateDatabase()</code>
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</p>
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<p>
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Deletes every record in the database and optionally returns the
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number of records that were deleted. Note that it is much less
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expensive to truncate a database without counting the number of
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records deleted than it is to truncate and count.
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</p>
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<a id="je_db5"></a>
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<pre class="programlisting">int numDiscarded =
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myEnv.truncate(null, // txn handle
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myDatabase.getDatabaseName(), // database name
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true); // If true, then the
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// number of records
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// deleted are counted.
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System.out.println("Discarded " + numDiscarded +
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" records from database " +
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myDatabase.getDatabaseName()); </pre>
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</li>
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</ul>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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||
<table width="100%" summary="Navigation footer">
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||
<tr>
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||
<td width="40%" align="left"><a accesskey="p" href="dbprops.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="databases.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dbUsage.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Database Properties </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Database Example</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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