HPjmeter 4.2 User's Guide

The Thread Histogram shows the number of threads existing in the observed period of time. By
selecting the smallest time interval, one minute, you can see an estimate of the number of
simultaneously active threads. Most operating systems have a limited capacity for the number
of threads a single process may create. Exceeding this capacity may cause a crash. Although
HPjmeter cannot indicate whether or not this will happen, the intensity of the new thread creation
may suggest deeper analysis is needed in this area.
Adjusting kernel parameters may increase the threads per process limit.
Sometimes an application may exhibit threads leak, when the number of dynamically created
threads is unconstrained and grows all the time. Tuning kernel parameters is unlikely to help
in this situation.
Related Topics
• Thread Histogram (page 131)
Identifying Excessive Method Compilation
HPjmeter allows you to enable an alert that identifies excessive method compilations. You can
then use the Method Compilation Count display to view the specific method or methods that
caused the alert.
Symptoms of excessive method compilation include poor application response because the JVM
is spending time re-compiling methods.
The Method Compilation Count display shows the methods that have been compiled, sorted by
number of compilations.
Figure 4-3 Example Metric: Method Compilation Count
Excessive method compilation is rare, especially with newer releases of JVM. Sometimes, due
to a defect in the JVM, a particular method can get repeatedly compiled, and de-optimized. This
means that the execution of this method oscillates between interpreter and compiled code.
However, due to the stress on the JVM, such phenomena are typically much more costly than
just running this method exclusively in interpreted mode.
Repeated compilation problems may result in SLO violations and will affect some or all
transactions. Read the JVM Release Notes to learn how to disable compilation of selected methods
for the HP Java HotSpot Virtual Machine.
46 Monitoring Applications