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264 lines
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HTML
264 lines
11 KiB
HTML
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<?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>Environment Properties</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="env.html" title="Chapter 2. Database Environments" />
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<link rel="prev" href="envclose.html" title="Closing Database Environments" />
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<link rel="next" href="envStats.html" title="Environment Statistics" />
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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">Environment Properties</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="envclose.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2. Database Environments</th>
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<td width="20%" align="right"> <a accesskey="n" href="envStats.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="EnvProps"></a>Environment Properties</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<dl>
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<dt>
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<span class="sect2">
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<a href="EnvProps.html#envconfig">The EnvironmentConfig Class</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="EnvProps.html#envhandleconfig">EnvironmentMutableConfig</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>
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You set properties for the <code class="classname">Environment</code> using the
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<code class="classname">EnvironmentConfig</code> class. You can also set properties for a
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specific <code class="classname">Environment</code> instance using
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<code class="classname">EnvironmentMutableConfig</code>.
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</p>
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<div class="sect2" 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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<h3 class="title"><a id="envconfig"></a>The EnvironmentConfig Class</h3>
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</div>
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</div>
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</div>
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<p>
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The <code class="classname">EnvironmentConfig</code> class makes a large number of fields and
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methods available to you. Describing all of these tuning parameters is beyond the scope of
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this manual. However, there are a few properties that you are likely to want to set. They
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are described here.
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</p>
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<p>
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Note that for each of the properties that you can commonly set, there is a corresponding
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getter method. Also, you can always retrieve the
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<code class="classname">EnvironmentConfig</code> object used by your environment using the
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<code class="methodname">Environment.getConfig()</code> method.
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</p>
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<p>
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You set environment configuration parameters using the following methods on the
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<code class="classname">EnvironmentConfig</code> class:
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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">EnvironmentConfig.setAllowCreate()</code>
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</p>
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<p>
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If <code class="literal">true</code>, the database environment is created when it is opened.
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If <code class="literal">false</code>, environment open fails if the environment does not
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exist. This property has no meaning if the database environment already exists.
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Default is <code class="literal">false</code>.
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</p>
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</li>
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<li>
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<p>
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<code class="methodname">EnvironmentConfig.setReadOnly()</code>
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</p>
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<p>If <code class="literal">true</code>, then all databases opened in this
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environment must be opened as read-only. If you are writing a
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multi-process application, then all but one of your processes must set
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this value to <code class="literal">true</code>. Default is <code class="literal">false</code>.</p>
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<p>
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You can also set this property using the <code class="literal">je.env.isReadOnly</code>
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parameter in your <code class="filename"><span class="emphasis"><em>env_home</em></span>/je.properties</code> file.
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</p>
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</li>
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<li>
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<p>
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<code class="methodname">EnvironmentConfig.setTransactional()</code>
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</p>
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<p>If <code class="literal">true</code>, configures the database environment
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to support transactions. Default is <code class="literal">false</code>.</p>
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<p>
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You can also set this property using the <code class="literal">je.env.isTransactional</code>
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parameter in your <code class="filename"><span class="emphasis"><em>env_home</em></span>/je.properties</code> file.
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</p>
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</li>
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</ul>
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</div>
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<p>For example:</p>
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<a id="je_env3"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.Environment;
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import com.sleepycat.je.EnvironmentConfig;
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import java.io.File;
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...
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Environment myDatabaseEnvironment = null;
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try {
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EnvironmentConfig envConfig = new EnvironmentConfig();
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envConfig.setAllowCreate(true);
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envConfig.setTransactional(true);
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myDatabaseEnvironment =
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new Environment(new File("/export/dbEnv"), envConfig);
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} catch (DatabaseException dbe) {
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System.err.println(dbe.toString());
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System.exit(1);
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} </pre>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="envhandleconfig"></a>EnvironmentMutableConfig</h3>
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</div>
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</div>
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</div>
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<p>
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<code class="classname">EnvironmentMutableConfig</code> manages properties that can be reset after the
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<code class="classname">Environment</code> object has been constructed. In addition, <code class="classname">EnvironmentConfig</code>
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extends <code class="classname">EnvironmentMutableConfig</code>, so you can set these mutable properties at
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<code class="classname">Environment</code> construction time if necessary.
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</p>
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<p>
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The <code class="classname">EnvironmentMutableConfig</code> class allows you to set the following
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properties:
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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="literal">setCachePercent()</code>
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</p>
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<p>
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Determines the percentage of JVM memory available to the JE cache.
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See
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<a class="xref" href="cachesize.html" title="Sizing the Cache">Sizing the Cache</a>
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for more information.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">setCacheSize()</code>
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</p>
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<p>
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Determines the total amount of memory available to the database cache.
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See <a class="xref" href="cachesize.html" title="Sizing the Cache">Sizing the Cache</a>
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for more information.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">setTxnNoSync()</code>
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</p>
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<p>
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Determines whether change records created due to a transaction commit are written to the backing
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log files on disk. A value of <code class="literal">true</code> causes
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the data to not be flushed to
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disk. See the <em class="citetitle">Berkeley DB, Java Edition Getting Started with Transaction Processing</em> guide.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">setTxnWriteNoSync()</code>
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</p>
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<p>
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Determines whether logs are flushed on transaction commit (the logs are still written, however).
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By setting this value to <code class="literal">true</code>, you potentially gain better performance than if
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you flush the logs on commit, but you do so by losing some of your transaction durability guarantees.
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</p>
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</li>
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</ul>
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</div>
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<p>
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There is also a corresponding getter method (<code class="methodname">getTxnNoSync()</code>).
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Moreover, you can always retrieve your environment's
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<code class="classname">EnvironmentMutableConfig</code> object by
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using the <code class="methodname">Environment.getMutableConfig()</code> method.
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</p>
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<p>
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For example:
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</p>
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<a id="je_env4"></a>
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<pre class="programlisting">package je.gettingStarted;
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import com.sleepycat.je.DatabaseException;
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import com.sleepycat.je.Environment;
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import com.sleepycat.je.EnvironmentMutableConfig;
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import java.io.File;
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...
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try {
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Environment myEnv = new Environment(new File("/export/dbEnv"), null);
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EnvironmentMutableConfig envMutableConfig =
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new EnvironmentMutableConfig();
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envMutableConfig.setTxnNoSync(true);
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myEnv.setMutableConfig(envMutableConfig);
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} catch (DatabaseException dbe) {
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// Exception handling goes here
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} </pre>
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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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|||
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<tr>
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|||
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<td width="40%" align="left"><a accesskey="p" href="envclose.html">Prev</a> </td>
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|||
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<td width="20%" align="center">
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|||
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<a accesskey="u" href="env.html">Up</a>
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|||
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</td>
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|||
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<td width="40%" align="right"> <a accesskey="n" href="envStats.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">Closing Database Environments </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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|||
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<td width="40%" align="right" valign="top"> Environment Statistics</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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