Isuru's Blog

My first Hackernoon story was published today. The story is " Profiling Java Applications with Async Profiler " With " Async Profiler ", both system code paths and Java code paths can be profiled with the help of AsyncGetCallTrace (an internal HotSpot JVM API) and perf_events . Async profiler supports several types of profiling. For example, CPU profiling Allocation profiling Wall-clock profiling Lock profiling The Hackernoon story demonstrates few examples of using Async Profiler and generating Flame Graphs as the output.

Have you seen " ~ UNCLASSIFIABLE ~.() " in the Call Tree Tab when analyzing a Flight Recording in Java Mission Control? That means, you have stack traces with more than 64 frames. The default stack depth in Java Flight Recorder is 64 and it can be changed with stackdepth option in -XX:FlightRecorderOptions flag. Please read my Medium story for more details on the Stack Depth in Java Flight Recorder .

When you are using Java Flight Recorder (JFR), the JFR will use an event settings file to check which event types to record. By default in JFR, there are two settings, "default" and "profile". The default setting is recommended for Continuous Recordings as it has very low overhead (typically less than 1% overhead). The profile setting has more events and useful when profiling the application. As mentioned in my previous blog post regarding  Java Flight Recorder Continuous Recordings , we use following arguments to do a Continuous Recording. -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:FlightRecorderOptions=defaultrecording=true,disk=true,repository=./tmp,dumponexit=true,dumponexitpath=./ Note: According to the Oracle documentation on " java " command, we should be able to specify "settings" parameter to the -XX:FlightRecorderOptions. However, the settings parameter has no effect when used with the -XX:FlightRecorderOptions and ...

When we are trying to find performance issues, it is sometimes necessary to do continuous recordings with Java Flight Recorder. Usually we debug issues in an environment similar to a production setup. That means we don't have a desktop environment and we cannot use Java Mission Control for flight recording. That also means we need to record & get dumps using command line in servers. We can of course use remote connection methods, but it's more easier to get recordings from the server. With continuous recordings, we need to figure out how to get dumps. There are few options. Get a dump when the Java application exits. For this, we need to use dumponexit and dumponexitpath options. Get a dump manually from JFR.dump diagnostic command via " jcmd " Note: The "jcmd" command is in $JAVA_HOME/bin. If you use the  Oracle Java Installation script for Ubuntu , you can directly use "jcmd" without including  $JAVA_HOME/bin in $PATH. Enabl...

Last year, I got two opportunities to talk about Java Mission Control & Java Flight Recorder. I first talked about " Using Java Mission Control & Java Flight Recorder " as an internal tech talk at WSO2 . I must thank Srinath for giving me that opportunity. After that, Prabath also invited me to do a talk at Java Colombo Meetup . Prabath, Thank you for inviting me and giving me the opportunity to talk at the Java Colombo Meetup! I'm also very excited to see that Marcus Hirt , the Team Lead for Java Mission Control has mentioned about the Java Colombo Meetup in his blog post: " My Favourite JMC Quotes ". It's so nice to see "Sri Lanka" was mentioned in his blog post! :) From Marcus' Blog Here are the slides used at the meetup. Java Colombo Meetup: Java Mission Control & Java Flight Recorder from Isuru Perera Marcus Hirt's blog posts really helped me to understand JMC & JFR concepts and his t...