etsangsplk / instana-javaagent

javaagent to initialize JVM attach and instrumentation APIs at JVM startup.

Instana JVM Startup Agent

The Instana agent architecture is modular. When the Instana agent runs, it will perform a runtime attach to any JVM and load the required classes lazily.

Compatibility tests however have shown that certain versions of J9 do not support all required features when no -javaagent was present on the JVM start command line. J9 will log a message like this:

*** java.lang.instrument ASSERTION FAILED ***: "jvmtierror == JVMTI_ERROR_NOT_AVAILABLE" at JPLISAgent.c line: 1009

Additionally tests have shown that the first runtime attach can cause a short pause when the JVM starts the necessary services for the agent.

For those reasons we recommend to start the JVM with this javaagent like this:

java -javaagent:instana-javaagent-1.0.0.jar -jar app.jar server

The latest version of that jar can be found in MavenCentral -> Instana.

Should the J9 that is used be a Java 8 updated with recent fixpacks, this is no longer necessary, but an command line switch can be used instead. Since as of "Java 8 - Service refresh 3 fix pack 22 (Dec 2016)" an option exists which basically performs the same:

-XX:+EnableHCR

Use the -XX:+EnableHCR option to enable late attached agents to redefine or retransform classes. 
This option might incur a performance penalty. This option is temporary and deprecated and will
be removed in a future update when no longer necessary.