Presentation delivered by Matt Brasier at DOAG German Oracle User Group Conference in Nuremberg, 19-21 November 2013. This lab will demonstrate the depth and breadth of the information available via the JMX API. We will use the JVM tools to peer deep into the workings of the JVM and understand how to identify and solve common performance bottlenecks. Attendees will get hands-on experience of using tools like VisualVM and Jstat to interrogate the JVM, and how to interpret the data returned. This lab will be a hands-on session that allows attendees to understand the power available to them in some of the overlooked core JVM tools (jstack, jstat, visualvm). The session will use a combination of slides and examples that the attendees can code-along with on their own laptops, and will focus primarily on how the tools can be used to identify performance bottlenecks, although we will also look at how you can expose your own application MBeans and use these to monitor the application. In my work as a Java performance consultant, I have found that JMX and the basic JVM tooling that uses it, is not understood by developers, so this session is about raising awareness of these tools and allowing developers to get inside the JVM and their application to understand how it works (and write better code). In my experience, once developers understand the power of JMX and VisualVM, they find it very interesting, and often the best way to demonstrate it is by allowing people to work with it. The fact that the base JDK is all that is required to demonstrate this means that there are few pre-requisites for this session, and because it is based on a low level technology, it is of interest to people working on all aspects of Java. I think this could make popular talk which will help developers understand the magic and power behind the Java Virtual Machine.

1. Through the JMX Window
Matt Brasier
Head of Consulting
C2B2 Consulting
© C2B2 Consulting Limited 2013
All Rights Reserved

2. Who am I?
• Head of consulting at C2B2
• Application server consultant
– WebLogic 5.1->Present
– JBoss 3.x -> Present
– Tomcat, etc
• Performance tuning and critical situation
support
• Author
© C2B2 Consulting Limited 2013
All Rights Reserved

3. Agenda
•
•
•
•
•
What is JMX?
JMX tools
What information does it expose?
What operations can JMX expose?
Exposing your own information and
operations
© C2B2 Consulting Limited 2013
All Rights Reserved

4. WHAT IS JMX?
© C2B2 Consulting Limited 2013
All Rights Reserved

5. What is JMX
• Java Management
eXtensions
• Currently at version 1.4
• http://docs.oracle.com/
javase/7/docs/technote
s/guides/jmx/JMX_1_4_
specification.pdf
“The Java Management
extensions (also called
the JMX specification)
define an architecture,
the design patterns, the
APIs, and the services
for application and
network management
and monitoring in the
Java programming
language.”
© C2B2 Consulting Limited 2013
All Rights Reserved

6. JMX History
• 1998 – JMX starts as JSR • JMAPI – Java Management
API, failed Sun project
3. EG composed of most
J2EE vendors, based on • JDMK – Java Dynamic
Management Kit, another
JDMK
failed Sun project
• 2003 – J2EE 1.4
• JMX
incorporates JMX in the
J2EE Spec
• 2004 – With Java 5
release, JMX becomes
part of the JDK/Java SE
© C2B2 Consulting Limited 2013
All Rights Reserved

7. What is management?
• Management Information
– Any information that is useful for the runtime
management of the application.
• Management Operations
– Any operations that can assist in the runtime
management of the application.
© C2B2 Consulting Limited 2013
All Rights Reserved

8. Why JMX?
• Application Management is important!
– If often forgotten.
• Standardise the APIs and patterns for exposing
management operations and tooling.
– Tools can be sure information is in an expected
format.
– Applications can take advantage of existing
tooling.
© C2B2 Consulting Limited 2013
All Rights Reserved

9. Core Concepts
• MBean
– Management Bean
• Operations
• Attributes
• MBean Server
– Registry for MBeans
• API
– Remote and local access to MBean Server and
MBeans
© C2B2 Consulting Limited 2013
All Rights Reserved

10. Core Concepts
• Applications/Frameworks/Containers expose
MBeans
• The JVM contains an MBeanServer which
registers all MBeans
• Clients use the JMX API to connect to the
MBeanServer and find relevant MBeans
• Clients read/change values of attributes and
invoke operations to manage the service
© C2B2 Consulting Limited 2013
All Rights Reserved

11. JMX TOOLS
© C2B2 Consulting Limited 2013
All Rights Reserved

12. JMX Tools
• JConsole
• JVisualVM
• Monitoring tools
– Hyperic HQ
– Nagios
– Etc
© C2B2 Consulting Limited 2013
All Rights Reserved

13. Demo
© C2B2 Consulting Limited 2013
All Rights Reserved

14. WHAT INFORMATION DOES IT
EXPOSE?
© C2B2 Consulting Limited 2013
All Rights Reserved

15. Default JMX info
• Heap Use
–
–
–
–
java.lang:type=Memory
java.lang:type=MemoryPool,name=Eden Space
java.lang:type=MemoryPool,name=Tenured Gen
java.lang:type=MemoryPool,name=Perm Gen
• Garbage collection
– java.lang:type=GarbageCollector,name=MarkSweepCompact
– java.lang:type=GarbageCollector,name=Copy
• Operating system info
– java.lang:type=OperatingSystem
© C2B2 Consulting Limited 2013
All Rights Reserved

16. Default JMX info
• Runtime JVM parameters
– java.lang:type=Runtime
• NIO Buffers
– java.nio:type=BufferPool,name=direct
• JDK Logger
– java.util.logging:type=Logging
• Classloading
– java.lang:type=ClassLoading
• And more!
© C2B2 Consulting Limited 2013
All Rights Reserved

17. In an application server
• Connection pool info
– Sizes
– Free connections
• Servlet/JSP info
– Number of requests
– Number of errors
• Thread pools
– Sizes
• JMS
– Queue sizes
– Pending messages
• EJBs
– Pool sizes
– Cache hit rates
• Connectors
– In coming request
volumes
© C2B2 Consulting Limited 2013
All Rights Reserved

18. WHAT OPERATIONS DOES IT
EXPOSE?
© C2B2 Consulting Limited 2013
All Rights Reserved

19. Default operations
• com.sun.management:type=HotSpotDiagnostic
– dumpHeap
– setVMOption
– getVMOption
• java.lang:type=Memory
– Gc
• java.lang:type=Threading
– dumpAllThreads
– findDeadLockedThreads
© C2B2 Consulting Limited 2013
All Rights Reserved

20. In an application server
• Datasources
– Reset all datasources
• JMS
– Delete all messages
• Server
– Restart or stop a server
• Deployment
– Deploy or redeploy applications
© C2B2 Consulting Limited 2013
All Rights Reserved

21. In an application server
• Any operation you
could normally perform
to manage an
application server!
• It is like an X-ray of your
application
© C2B2 Consulting Limited 2013
All Rights Reserved

22. EXPOSING YOUR OWN
MANAGEMENT INFORMATION AND
OPERATIONS
© C2B2 Consulting Limited 2013
All Rights Reserved

23. Two step process
• Create MBeans
• Register with MBean
server
• Profit
© C2B2 Consulting Limited 2013
All Rights Reserved

24. Create MBeans
• Identify where in your application you have
relevant management information
• Create an MBean interface
• Implement the MBean interface
© C2B2 Consulting Limited 2013
All Rights Reserved

25. MBean Interface
public Interface LocationMonitorMBean
{
public void getNumberOfFiles();
public void setScanPeriod();
public void getScanPeriod();
public void resetFileCounter();
public void disable();
public void enable();
public void getEnabled();
}
Getters and Setters represent
Attributes
Other methods represent
operations
© C2B2 Consulting Limited 2013
All Rights Reserved

26. Implementation class
• Implement the MBean interface
– You can do this with an existing class
• Try and avoid doing intensive work in the
MBean implementation
– Pre-compute values
– Periodically check and cache values
© C2B2 Consulting Limited 2013
All Rights Reserved

27. Implementation class
public class LocationMonitor implements LocationMonitorMBean
{
private boolean enabled;
Attributes are accessed via getters/setters
private long scanInterval;
private long numFiles;
public void getNumberOfFiles(
{
return numFiles;
...
© C2B2 Consulting Limited 2013
All Rights Reserved

28. Register with MBeanServer
• Create (or get hold of) an instance of your
MBean implementation
• Get hold of an MBean Server
– PlatformMBeanServer
• Create an ObjectName for your MBean
• Register the MBean
© C2B2 Consulting Limited 2013
All Rights Reserved

29. Register with MBeanServer
public static void main(String[] args) throws Exception
Get the MBean Server
{
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
ObjectName name = new
Create the ObjectName
ObjectName(“uk.co.c2b2.management:type=LocationMonitor");
Create the MBean instance
LocationMonitor mbean = new LocationMonitor();
mbs.registerMBean(mbean, name);
Register it
}
© C2B2 Consulting Limited 2013
All Rights Reserved

30. What to monitor
• Resources that your application uses
– Including data (flow rates etc)
• Expose management operations
– Restarting components
– Re-loading configuration files
© C2B2 Consulting Limited 2013
All Rights Reserved

31. What is through the JMX window?
• A future with more
Information
• A future with more
control
© C2B2 Consulting Limited 2013
All Rights Reserved

32. QUESTIONS?
© C2B2 Consulting Limited 2013
All Rights Reserved