je/docs/GettingStartedGuide/EnvProps.html

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<title>Environment Properties</title>
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<p>Library Version 12.2.7.5</p>
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<th colspan="3" align="center">Environment Properties</th>
</tr>
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<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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<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>
<p>
You can also set this property using the <code class="literal">je.env.isReadOnly</code>
parameter in your <code class="filename"><span class="emphasis"><em>env_home</em></span>/je.properties</code> file.
</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>
<p>
You can also set this property using the <code class="literal">je.env.isTransactional</code>
parameter in your <code class="filename"><span class="emphasis"><em>env_home</em></span>/je.properties</code> file.
</p>
</li>
</ul>
</div>
<p>For example:</p>
<a id="je_env3"></a>
<pre class="programlisting">package je.gettingStarted;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.Environment;
import com.sleepycat.je.EnvironmentConfig;
import java.io.File;
...
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);
} </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 JE cache.
See
<a class="xref" href="cachesize.html" title="Sizing the Cache">Sizing the Cache</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="Sizing the Cache">Sizing the Cache</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">Berkeley DB, Java Edition Getting Started with Transaction Processing</em> guide.
</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.
</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>
<a id="je_env4"></a>
<pre class="programlisting">package je.gettingStarted;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.Environment;
import com.sleepycat.je.EnvironmentMutableConfig;
import java.io.File;
...
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
} </pre>
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