Database Reference
In-Depth Information
Figure9-1.The JMX architecture
The JMX architecture is simple. The JVM collects information from the underlying operating
system. The JVM itself is instrumented, so many of its features are exposed for management as
described earlier. An instrumented Java application (such as Cassandra) runs on top of this, also
exposing some of its features as manageable objects. The JDK includes an MBean server that
makes the instrumented features available over a remote protocol to a JMX Management Ap-
plication. The JVM also offers management capabilities to Simple Network Monitoring Protocol
(SNMP) agents and works in a similar manner.
But within a given application, you can manage only what the application developers have made
available for you to manage. Luckily, the Cassandra developers have instrumented large parts of
the database, making management via JMX fairly straightforward.
This instrumentation of a Java application is performed by wrapping the application code that
you want JMX to hook into with managed beans.
MBeans
A managedbean, or MBean, is a special type of Java bean that represents a single manageable
resource inside the JVM. MBeans interact with an MBean server to make their functions re-
motely available.
The
jconsole
tool ships with the standard Java Development Kit. It provides a graphical user
interface client for working with MBeans and can be used for local or remote management. A
view of JConsole is shown in
Figure 9-2
.
