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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<title>Environment Properties</title>
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<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 11.2.5.3</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Environment Properties</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="EnvClose.html">Prev</a> </td>
<th width="60%" align="center">Chapter 2. Database Environments</th>
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<hr />
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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="EnvProps"></a>Environment Properties</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="EnvProps.html#envconfig">The EnvironmentConfig Class</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="EnvProps.html#envhandleconfig">EnvironmentMutableConfig</a>
</span>
</dt>
</dl>
</div>
<p>You set properties for the <code class="classname">Environment</code> using
the <code class="classname">EnvironmentConfig</code> class. You can also set properties for a specific
<code class="classname">Environment</code> instance using <code class="classname">EnvironmentMutableConfig</code>.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="envconfig"></a>The EnvironmentConfig Class</h3>
</div>
</div>
</div>
<p>
The <code class="classname">EnvironmentConfig</code> class makes a
large number of fields and methods available to you. Describing all of these
tuning parameters is beyond the scope of this manual. However, there are a
few properties that you are likely to want to set. They are described
here.</p>
<p>Note that for each of the properties that you can commonly set, there is a
corresponding getter method. Also, you can always retrieve the
<code class="classname">EnvironmentConfig</code> object used by your environment
using the <code class="methodname">Environment.getConfig()</code> method.
</p>
<p>
You set environment configuration parameters using the following methods on the
<code class="classname">EnvironmentConfig</code> class:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="methodname">EnvironmentConfig.setAllowCreate()</code>
</p>
<p>If <code class="literal">true</code>, the database environment is created
when it is opened. If <code class="literal">false</code>, environment open fails if the environment
does not exist. This property has no meaning if the database
environment already exists. Default is <code class="literal">false</code>.</p>
</li>
<li>
<p>
<code class="methodname">EnvironmentConfig.setReadOnly()</code>
</p>
<p>If <code class="literal">true</code>, then all databases opened in this
environment must be opened as read-only. If you are writing a
multi-process application, then all but one of your processes must set
this value to <code class="literal">true</code>. Default is <code class="literal">false</code>.</p>
</li>
<li>
<p>
<code class="methodname">EnvironmentConfig.setTransactional()</code>
</p>
<p>If <code class="literal">true</code>, configures the database environment
to support transactions. Default is <code class="literal">false</code>.</p>
</li>
</ul>
</div>
<p>For example:</p>
<pre class="programlisting">package db.gettingStarted;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.Environment;
import com.sleepycat.db.EnvironmentConfig;
import java.io.File;
import java.io.FileNotFoundException;
...
Environment myDatabaseEnvironment = null;
try {
EnvironmentConfig envConfig = new EnvironmentConfig();
envConfig.setAllowCreate(true);
envConfig.setTransactional(true);
myDatabaseEnvironment =
new Environment(new File("/export/dbEnv"), envConfig);
} catch (DatabaseException dbe) {
System.err.println(dbe.toString());
System.exit(1);
} catch (FileNotFoundException fnfe) {
System.err.println(fnfe.toString());
System.exit(-1);
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="envhandleconfig"></a>EnvironmentMutableConfig</h3>
</div>
</div>
</div>
<p>
<code class="classname">EnvironmentMutableConfig</code> manages properties that can be reset after the
<code class="classname">Environment</code> object has been constructed. In addition, <code class="classname">EnvironmentConfig</code>
extends <code class="classname">EnvironmentMutableConfig</code>, so you can set these mutable properties at
<code class="classname">Environment</code> construction time if necessary.
</p>
<p>
The <code class="classname">EnvironmentMutableConfig</code> class allows you to set the following
properties:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">setCachePercent()</code>
</p>
<p>
Determines the percentage of JVM memory available to the DB cache.
See <a class="xref" href="cachesize.html" title="Selecting the Cache Size">Selecting the Cache Size</a>
for more information.
</p>
</li>
<li>
<p>
<code class="literal">setCacheSize()</code>
</p>
<p>
Determines the total amount of memory available to the database cache.
See <a class="xref" href="cachesize.html" title="Selecting the Cache Size">Selecting the Cache Size</a>
for more information.
</p>
</li>
<li>
<p>
<code class="literal">setTxnNoSync()</code>
</p>
<p>
Determines whether change records created due to a transaction commit are written to the backing
log files on disk. A value of <code class="literal">true</code> causes
the data to not be flushed to
disk. See the
<em class="citetitle">Getting Started with Transaction Processing for Java</em>
guide for more information.
</p>
</li>
<li>
<p>
<code class="literal">setTxnWriteNoSync()</code>
</p>
<p>
Determines whether logs are flushed on transaction commit (the logs are still written, however).
By setting this value to <code class="literal">true</code>, you potentially gain better performance than if
you flush the logs on commit, but you do so by losing some of your transaction durability guarantees.
See the
<em class="citetitle">Getting Started with Transaction Processing for Java</em>
guide for more information.
</p>
</li>
</ul>
</div>
<p>
There is also a corresponding getter method (<code class="methodname">getTxnNoSync()</code>).
Moreover, you can always retrieve your environment's
<code class="classname">EnvironmentMutableConfig</code> object by
using the <code class="methodname">Environment.getMutableConfig()</code> method.
</p>
<p>
For example:
</p>
<pre class="programlisting">package db.gettingStarted;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.Environment;
import com.sleepycat.db.EnvironmentMutableConfig;
import java.io.File;
import java.io.FileNotFoundException;
...
try {
Environment myEnv = new Environment(new File("/export/dbEnv"), null);
EnvironmentMutableConfig envMutableConfig =
new EnvironmentMutableConfig();
envMutableConfig.setTxnNoSync(true);
myEnv.setMutableConfig(envMutableConfig);
} catch (DatabaseException dbe) {
// Exception handling goes here
} catch (FileNotFoundException fnfe) {
// Exception handling goes here
}</pre>
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<a accesskey="u" href="Env.html">Up</a>
</td>
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</tr>
<tr>
<td width="40%" align="left" valign="top">Closing Database Environments </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
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<td width="40%" align="right" valign="top"> Part I. Programming with the Direct Persistence Layer</td>
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