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=== Tuning

==== Garbage Collection

Like any Java applications, Apache Karaf uses a JVM. An important feature of the JVM is the Garbage Collector.

Apache Karaf default configuration is sized for small to medium needs and to work on most machine.

That's why this default configuration may appear like "small".

By default, Apache Karaf uses:

* `-Xms128M`
* `-Xmx512M`
* `-XX:+UnlockDiagnosticVMOptions`

On Sun/Oracle JVM:

* the Perm size is the JVM default (for Java 7)

On IBM JVM and AIX system:

* `-Xverify:none`
* `-Xdump:heap`
* `-Xlp`

For any container, it's always difficult to predict the usage of the resources and the behaviour of the artifacts deployed.

Generally speaking, a good approach for tuning is to enable `-verbose:gc` and use tools like VisualVM to identify the potentials
memory leaks, and see the possible optimisation of the spaces and GC.

You can find introduction about GC here: [http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/gc01/index.html].

===== Java 6

If you have enough resources available on the machine, a good configuration may be:

* `-server`
* `-Xmx1024M`
* `-XX:MaxPermSize=640M`
* `-XX:+UseConcMarkSweepGC`
* `-XX:+UseParNewGC`
* `-XX:+CMSClassUnloadingEnabled`

It will give more resources to Apache Karaf, and avoid some perm space saturation if you do a lot of bundles refresh.

See http://www.oracle.com/technetwork/java/javase/gc-tuning-6-140523.html for details about Java 6 tuning.

===== Java 7

Java 7 introduces a new GC algorithm: the GC1.

Depending of the use cases (and usage of the heap), the new GC1 algorithm can give good performance improvements:

* `-XX:+UseG1GC`
* `-XX:-UseAdaptiveSizePolicy`

See http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html for details about Java 7 GC1 tuning.

You can find a good article about Java 7 tuning here: http://java-is-the-new-c.blogspot.de/2013/07/tuning-and-benchmarking-java-7s-garbage.html

==== Threads

In high loaded system, the number of threads can be very large.

===== WebContainer

If you use the Apache Karaf WebContainer, the Jetty connectors create threads to handle the incoming HTTP requests.

The `etc/jetty.xml` configuration file allows you to tune the Jetty connector.

For instance, the following connector configuration:

----
    <Call name="addConnector">
        <Arg>
            <New class="org.eclipse.jetty.server.nio.SelectChannelConnector">
                <Set name="host">
                    <Property name="jetty.host" />
                </Set>
                <Set name="port">
                    <Property name="jetty.port" default="8181" />
                </Set>
                <Set name="maxIdleTime">300000</Set>
                <Set name="Acceptors">2</Set>
                <Set name="statsOn">false</Set>
                <Set name="confidentialPort">8443</Set>
                <Set name="lowResourcesConnections">20000</Set>
                <Set name="lowResourcesMaxIdleTime">5000</Set>
            </New>
        </Arg>
    </Call>
----

defines the following properties:

* `maxIdleTime` is the maximum inactivity time for a connection.
* `lowResourcesConnections` defines the number of connections. If the current number of connections is greater than
 this value, the status is "low on resources". In that case, a new connection timeout is applied: the `lowResourceMaxIdleTime`.
* `Acceptors` defines the number of threads for incoming connections.

===== Apache Camel

For instance, if you use Apache Camel inside Apache Karaf, Camel components can create a lot of threads.

Apache Camel use the notion of `threadPoolProfile` to control the threads creation.

For instance, the following Camel configuration defines a pool creation strategy:

----
<threadPoolProfile id="defaultThreadPoolProfile" defaultProfile="true"
                   poolSize="10" maxPoolSize="20" maxQueueSize="1000"
                   rejectedPolicy="CallerRuns"/>
----

See the http://camel.apache.org for details.

===== Apache CXF

Apache CXF uses workqueues to handle server request/response.

You may see a `etc/org.apache.cxf.workqueues-default.cfg` configuration file. It's the default configuration applied
to all workqueues (a workqueue can be associated to a specific endpoint).

On a workqueue, you can define the following properties about the threads:

* `org.apache.cxf.workqueue.default.highWaterMark` defines the maximum number of threads.
* `org.apache.cxf.workqueue.default.lowWaterMark` defines the minimum number of threads.
* `org.apache.cxf.workqueue.default.initialSize` defines the initial number of threads.

See the http://cxf.apache.org for details.

==== System packages

The `etc/jre.properties` defines the packages directly provided by the JVM.

Most of the time, the default configuration in Apache Karaf is fine and works in most of the use cases.

However, some times, you may want to not use the packages provided by the JVM, but the same packages provided by a bundle.

For instance, the JAXB version provided by the JVM is "old", and you want to use new JAXB bundles.

In that case, you have to comment the packages in `etc/jre.properties` to avoid to be provided by the JVM and use the
ones from the bundles.