JVM trace can aid in the diagnosis of problems in the Java Virtual Machine
(JVM). Note that JVM trace can produce a large amount of output, so you should
normally activate JVM trace for special transactions, rather than turning
it on globally for all transactions.
Controlling tracing for JVMs tells you about the different ways to activate JVM
tracing and change the JVM trace options. To summarize, you can control JVM
trace using:
- The CICS-supplied transaction CETR, which you can use to change the JVM
trace options, and to activate JVM tracing. You can use the CETR transaction
to define JVM tracing dynamically on the running CICS system.
- The CICS system initialization parameters JVMLEVEL0TRACE, JVMLEVEL1TRACE,
JVMLEVEL2TRACE, and JVMUSERTRACE, which you can use to set the default JVM
trace options for the CICS region, and the SPCTRSJ and STNTRSJ system initialization
parameters, which you can use to activate JVM tracing. You can only supply
these parameters at CICS startup time; you cannot define them in the DFHSIT
macro. You can use this method to define tracing for JVMs at CICS initialization.
- The EXEC CICS INQUIRE JVMPOOL and EXEC CICS SET JVMPOOL commands (but
not their CEMT equivalents), which you can use to change the current JVM trace
options for the CICS region.
- The EXEC CICS SET TRACETYPE command, which you can use to activate JVM
tracing.
- The ibm.dg.trc.external system property in the JVM
properties file that is referenced by the JVM profile for a JVM, which you
can use to set and activate initial trace options for a particular JVM. You
should only use this system property with care.
The first two methods, using CETR and using the CICS system initialization
parameters, are most similar to the methods that you would use to define tracing
for other components.
When you set trace levels 29–32 for the SJ component and activate
JVM trace, each JVM trace point that is generated appears as an instance of
CICS trace point SJ 4D01. If the JVM trace facility fails, CICS issues the
trace point SJ 4D00.
In addition to the JVM trace options, the standard trace points for the
SJ (JVM) domain, at CICS trace levels 0, 1 and 2, can be used to trace the
actions that CICS takes in setting up and managing JVMs and the shared class
cache. The SJ domain includes a level 2 trace point SJ 0224, which shows you
a history of the programs that have used each JVM. “JVM domain trace points” in CICS® Trace Entries has details of all the
standard trace points in the SJ domain.