Isuru's Blog

I wrote a Medium story about " Using Java Flight Recorder " in last year. The story is a bit long, but it has all the details you need to know when you want to start using Java Flight Recorder (JFR). Read more at " Using Java Flight Recorder ". Thank you!

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 ...

Flame Graphs Brendon D. Gregg , who is a computer performance analyst , has created  Flame Graphs to visualize stack traces in an interactive way. You must watch his talk at USENIX/LISA13 , titled Blazing Performance with Flame Graphs , which explains Flame Graphs in detail. There can be different types of flame graphs and I'm focusing on  CPU Flame Graphs  with Java in this blog post. Please look at the Flame Graphs Description  to understand the Flame Graph visualization. CPU Flame Graphs and Java Stack Traces As  Brendon  mentioned in his talk, understanding why CPUs are busy is very important when analyzing performance.  CPU Flame Graphs  is a good way to identify hot methods from sampled stack traces. In order to generate CPU Flame Graphs for Java Stack Traces , we need a way to get sample stack traces. Brendon has given examples to use jstack  and Google's lightweight-java-profiler . Please r...

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...