Database Reference
In-Depth Information
Heap M
y Usage
This shows the total memory available to the Cassandra program, as well as how much it's
using right now.
p Memory U
Threads
This is the number of live threads Cassandra is using.
Cllasses
The number of classes that Cassandra has loaded. This number is relatively small for such a
powerful program; Cassandra typically requires around 2,300 classes out of the box. Com-
pare this to a program such as Oracle WebLogic, which typically loads around 24,000
classes.
CPU U
U Usage
This shows the percentage of the processor that the Cassandra program is currently using.
You can use the selector to adjust the time range shown in the charts.
If you want to see a more detailed view of how Cassandra is using the Java heap and nonheap
memory, click the Memory tab. By changing the chart value in the drop-down, you can see in
detail the graduations in which Cassandra is using its memory. You can also (try to) force a
garbage collection if you think it's necessary.
You can connect to more than one JMX agent at once. Just choose File > New Connection... and
repeat the steps to connect to another running Cassandra node to view multiple servers at once.
Cassandra's MBeans
Once you've connected with a JMX agent such as JConsole, you can manage Cassandra using the
MBeans it exposes. To do so, click the MBeans tab. Other than the standard Java items available
to every agent, there are several Cassandra packages that contain manageable beans, organized
by their package names, which start with org.apache.cassandra. We won't go into detail on all of
them here, but there are several of interest that we'll take a look at.
Many classes in Cassandra are exposed as MBeans, which means in practical terms that they
implement a custom interface that describes the operations that need to be implemented and for
which the JMX agent will provide hooks. The steps are basically the same for getting any MBean
to work; I'll use a single key class as an example. If you'd like to JMX-enable something that isn't
already enabled, modify the source code following this general outline and you'll be in business.
