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* Copyright (c) 2015 Eclipse Foundation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* Contributors:
* Eric Poirier (Eclipse Foundation) - Initial implementation
<h1 class="article-title"><?php echo $pageTitle; ?></h1>
<h2>JVM Convergence</h2>
As Henrik St&aring;hl, VP of Product Management in the Java Platform
Group at Oracle outlined Oracle’s JVM strategy at the JavaOne
conference back in 2010, the high level plan presented to the
JavaOne audience and on Henrik’s blog foresaw that the best features
from HotSpot and JRockit would be merged into a single VM. Dubbed <i>JVM
convergence</i>, this process was expected to take multiple years.
<p>While the first fruits of this labor showed up in JDK 7, the bulk
of JVM convergence effort has been planned for JDK 8. A quick glance
at the planned JDK 8 feature list, which is available on the
corresponding OpenJDK Project’s web site, shows a number of
improvements in the JVM area, like the removal of the permanent
generation, that have been implemented for JDK 8 as part of the JVM
convergence effort.</p>
<p>Fortunately, you don’t have to wait until JDK 8 is released to
benefit from a small selection of the new JVM features, as a few of
them have, after careful backporting and testing, made their way
into JDK 7 Update releases. One of the most notable of them is Java
Mission Control, which is bundled with the HotSpot JVM starting with
the release of Oracle JDK 7 Update 40 (7u40).</p>
<p>Java Mission Control’s ancestor is JRockit Mission Control, the
production time profiling and diagnostics tools suite for the
JRockit JVM. For in-depth background and information on the JRockit
JVM and JRockit Mission Control, I’d recommend the book “Oracle
JRockit: The Definitive Guide” by Marcus Hirt and Marcus Lagergren.</p>
<p>What began as an effort to create tooling to analyze how real
production systems were using the JRockit JVM, evolved into an
efficient, low overhead way to gather and analyze telemetry data of
applications running on the JRockit JVM, allowing the development
team to reproduce and address customer issues without requiring
access to their source code, or their production environment.</p>
Instead of using more traditional and invasive techniques like
bytecode instrumentation (which has the obvious drawback that the so
instrumented application being analyzed is no longer made up of the
same bytecode that was running in production and exhibited some
interesting behavior) or JVMTI, Java Mission Control relies on a
‘flight recorder’ feature in the HotSpot JVM - which is accordingly
called <i>Java Flight Recorder</i>.
<p>Recordings of JVM telemetry data can be produced by the Java Flight
Recorder on demand, analyzed directly or stored for later analysis
inside Java Mission Control using the Flight Recorder tool. The data
includes an execution profile, memory allocation and garbage
collection statistics, optimization decisions, as well as
information on I/O and locking events. Given that its focus is on
gathering data with the lowest possible impact on the running
application, Java Mission Control is suitable for use in both
development and production environments.</p>
<p>Oracle Java Mission Control and Oracle Java Flight Recorder are
commercial features, which are available as part of the Oracle Java
SE Advanced product. They are freely available for download for
development and evaluation purposes as part of Oracle JDK 7 Update
40, as per the terms in the Oracle Binary Code License Agreement,
but require an Oracle Java SE Advanced license for production use.</p>
<h2>Getting Started</h2>
If you have downloaded and installed Oracle JDK 7 Update 40, or a
later release, you can start Java Mission Control by running the jmc
application in the <i>bin</i> directory of an Oracle JDK 7 Update 40
installation. If you are an Eclipse user, you’ll be greeted by a
familiar looking user interface - which may come as a surprise.
<p>Java Mission Control is built upon the Eclipse RCP technology. If
you are interested in the background and details behind getting an
Eclipse RCP based application into the JDK, I’d recommend the
upcoming “Experiences from building one of the world's most
distributed RCP apps” presentation at EclipseCon 2014 by Klara Ward
and Marcus Hirt from Oracle. And of course, if you’d like to see
Oracle Java Mission Control in action at EclipseCon, Marcus Hirt and
David Lindholm have a session titled “The new profiling tools in the
Oracle JDK!” that goes into the details.</p>
Besides the standalone Java Mission Control tool, if you instead
prefer to run your development tools inside the Eclipse IDE, the
Oracle Java Mission Control home page at <a target="_blank"
provides a pointer to the Eclipse Update site for the respective set
of plugins. For the best user experience, it is recommended to use
Eclipse IDE 3.8.2. Please note that in that case you’ll need to run
your Eclipse IDE on the JDK in order for all the feature of Java
Mission Control to work as expected. Detailed installation
instructions are linked off the Oracle Java Mission Control home
<h2>Using the JMX Console</h2>
<p>If you are familiar with the JConsole utility in the JDK, you’ll
find the Java Mission Control JXM Console easily accessible,
providing you with a superset of the functionality. For a start, it
lets you detect and connect to Java processes running either locally
on your machine, or remotely, through the Java Discovery Protocol
(JDP) or given a JMX agent URL.</p>
<p>Once connected, the JMX console allows you to monitor and visualize
the JMX data of the Java process, to take actions depending on the
observed values triggering conditions, to store recorded data for
later analysis, and, of course, to load it back into Java Mission
Control to take a deeper look into the observed behavior.</p>
<p>Typically, the JMX Console would be used to continuously monitor a
running process, by observing a small set of data of interest like
the CPU load or heap usage. Once a certain condition is met, the
console could be configured to dump the Flight Recorder data, for
example, for later evaluation.</p>
<h2>The Java Flight Recorder</h2>
<p>When something goes wrong unexpectedly, it’s very important to be
able to find out the exact circumstances in order to track down the
root cause of failure. The Java Flight Recorder can be thought of as
such a tool for the HotSpot JVM - it efficiently records information
about the JVM and its environment, for as long as it’s running. When
something interesting happens, the recorded data can be dumped and
stored for later, off-line analysis, or it can be simply stored on
an ongoing basis. It has a low performance impact, less then 2% for
typical Java applications, when collecting data and events.</p>
<h2>Creating Flight Recordings</h2>
In order to create flight recordings, you have to explicitly enable
the Java Flight Recorder in the HotSpot JVM you’d like to monitor by
passing a few additional flags to it upon startup. For details,
please consult the extensive Java Flight Recorder Runtime Guide
available at <a target="_blank"
<p>Recordings can be timed or continuous. Timed recordings run for a
given amount of time, and stop automatically once the time is up.
When you create a timed recording in Java Mission Control, it will
be automatically stored, downloaded and loaded into the tool for
analysis once the recording completes. Continuous recordings, on the
other hand, run until they are stopped by the end user.</p>
<p>While creating recordings directly from Java Mission Control is the
easiest choice for developers, users who need more flexibility can
use the jcmd command line tool, or pass command line flags to the
HotSpot JVM to get the desired behavior.</p>
<h2>Analyzing Flight Recordings</h2>
<p>Once you load up a flight recording in Java Mission Control, you
can look at a number of different areas like code, memory, threads,
locks and I/O and analyze various aspects of runtime behavior of
your application.</p>
<p>For example, for CPU-bound applications, the code view in the user
interface will let you drill down into hotspots of your application,
and discover optimization opportunities. If you’re tuning the GC, or
tracking down memory allocation issues, then you can use the memory
view to get a detailed view on individual GC events, allocation
sites, GC pauses, etc. You can visualize the latency profile of your
application by looking at I/O and Threads views, and even drill down
into a view representing individual events in the recording.</p>
<p>Fortunately, you don’t have to wait for Java 8 to try out Java
Mission Control and Java Flight Recorder. If you’re curious about
the Eclipse RCP based application in the Oracle JDK, as I hope you’d
be, check out the jmc application in the bin directory, and give it
a spin.</p>
<li><a target="_blank" href="">Oracle
Java Mission Control home page</a></li>
<li><a target="_blank"
href="">Demo video</a></li>
<li><a target="_blank"
<li><a target="_blank" href="">Marcus
Hirt’s blog</a></li>
<li><a target="_blank"
JVM Strategy</a></li>
<li><a target="_blank"
href="">Planned JDK
8 Features</a></li>
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