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<th colspan="3" align="center">Environment Properties</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>
</div>
<p>You set properties for the <tt class="classname">Environment</tt> using
the <tt class="classname">EnvironmentConfig</tt> class. You can also set properties for a specific
<tt class="classname">Environment</tt> instance using <tt class="classname">EnvironmentMutableConfig</tt>.
</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></div>
</div>
<p>
The <tt class="classname">EnvironmentConfig</tt> 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
<tt class="classname">EnvironmentConfig</tt> object used by your environment
using the <tt class="methodname">Environment.getConfig()</tt> method.
</p>
<p>
You set environment configuration parameters using the following methods on the
<tt class="classname">EnvironmentConfig</tt> class:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<tt class="methodname">EnvironmentConfig.setAllowCreate()</tt>
</p>
<p>If <tt class="literal">true</tt>, the database environment is created
when it is opened. If <tt class="literal">false</tt>, environment open fails if the environment
does not exist. This property has no meaning if the database
environment already exists. Default is <tt class="literal">false</tt>.</p>
</li>
<li>
<p>
<tt class="methodname">EnvironmentConfig.setReadOnly()</tt>
</p>
<p>If <tt class="literal">true</tt>, 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 <tt class="literal">true</tt>. Default is <tt class="literal">false</tt>.</p>
</li>
<li>
<p>
<tt class="methodname">EnvironmentConfig.setTransactional()</tt>
</p>
<p>If <tt class="literal">true</tt>, configures the database environment
to support transactions. Default is <tt class="literal">false</tt>.</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></div>
</div>
<p>
<tt class="classname">EnvironmentMutableConfig</tt> manages properties that can be reset after the
<tt class="classname">Environment</tt> object has been constructed. In addition, <tt class="classname">EnvironmentConfig</tt>
extends <tt class="classname">EnvironmentMutableConfig</tt>, so you can set these mutable properties at
<tt class="classname">Environment</tt> construction time if necessary.
</p>
<p>
The <tt class="classname">EnvironmentMutableConfig</tt> class allows you to set the following
properties:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<tt class="literal">setCachePercent()</tt>
</p>
<p>
Determines the percentage of JVM memory available to the DB cache.
See <a href="cachesize.html">Selecting the Cache Size</a>
for more information.
</p>
</li>
<li>
<p>
<tt class="literal">setCacheSize()</tt>
</p>
<p>
Determines the total amount of memory available to the database cache.
See <a href="cachesize.html">Selecting the Cache Size</a>
for more information.
</p>
</li>
<li>
<p>
<tt class="literal">setTxnNoSync()</tt>
</p>
<p>
Determines whether change records created due to a transaction commit are written to the backing
log files on disk. A value of <tt class="literal">true</tt> causes
the data to not be flushed to
disk. See the
<i class="citetitle">Getting Started with Transaction Processing for Java</i>
guide for more information.
</p>
</li>
<li>
<p>
<tt class="literal">setTxnWriteNoSync()</tt>
</p>
<p>
Determines whether logs are flushed on transaction commit (the logs are still written, however).
By setting this value to <tt class="literal">true</tt>, 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
<i class="citetitle">Getting Started with Transaction Processing for Java</i>
guide for more information.
</p>
</li>
</ul>
</div>
<p>
There is also a corresponding getter method (<tt class="methodname">getTxnNoSync()</tt>).
Moreover, you can always retrieve your environment's
<tt class="classname">EnvironmentMutableConfig</tt> object by
using the <tt class="methodname">Environment.getMutableConfig()</tt> 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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