| Measurement |
Description |
Measurement
Unit |
Interpretation |
| Total_classes_loaded |
Refers to the total number of classes that have been loaded since the Java virtual machine started execution.
|
Number |
|
| Classes_loaded |
Indicates the number of classes that have been loaded in the Java virtual machine since the last measurement period.
|
Number |
Classes are fundamental to the design of Java programming language. Like many server applications, Tomcat installs a variety of class loaders (that is,
classes that implement
java.lang.ClassLoader) to allow different portions of the container, and the web applications running
on the container, to have access to different repositories of available
classes and resources. A consistent decrease in the number of classes
loaded and unloaded could indicate a road-block in the
loading/unloading of classes by the class loader. If left unchecked, critical resources/classes could be
rendered inaccessible to web
applications, thereby severelyaffecting application performance.
|
| Classes_unloaded |
Indicates the total number of classes that have been unloaded in the Java virtual machine since the last measurement period.
|
Number |
| Total_daemon_threads |
Indicates the current number of live daemon threads.
|
Number |
The main function of the daemon threads is to provide service to other threads, running in the same
process as the daemon thread. If the value of this measure is equal to that of the Live_threads measure, then JVM would stop
executing; in other words, when the only remaining threads are the daemon threads, then JVM shuts
down and so does Tomcat.
|
| Live_threads |
Indicates the current number of live daemon and non daemon threads.
|
Number |
| Deadlock_threads |
Indicates the current number of deadlock threads.
|
Number |
Ideally the value of this measure should be 0.A non-zero valueindicates the occurrence of a deadlock. When a thread attempts to acquire a resource that is already locked by another thread, a
deadlock situation arises.
|
| Server_uptime |
Indicates the uptime of Java virtual machine.
|
Mins |
To ensure that the JVM is up and running for a long time, you need to make sure that atleast one non-daemon thread is executing at all times. This is because, without any non-daemon threads, the daemon threads have no recipients for the service it provides; Hence it brings down both the JVM and Tomcat.
|