Java Flight Recording and Analysis with Azul Mission Control
January 25, 2024Author(s)
Java Flight Recording (JFR) is a Java Virtual Machine (JVM) profiling and diagnostics tool. It enables you to collect and analyze data regarding the performance and behavior of a Java application. As JFR is included in the JVM, there is no need for additional tools or installations to make recordings of your applications.
By utilizing JFR, you gain valuable insights into the runtime behavior of your Java applications. It helps you to optimize performance, identify and troubleshoot issues, and ensure better overall reliability. JFR is designed with very low overhead, allowing its use in production environments with minimal impact on the performance of your application.
You can use a JFR recording to examine your application with various tools, such as Azul Mission Control.
Azul Mission Control
Based on the open-sourced "JDK Mission Control" tool, Azul Mission Control monitors, profiles, and troubleshoots Java applications running in a JVM.
Leveraging JFR, it provides a detailed and efficient analysis of a running Java application with minimal overhead on the JVM. It can also analyze an existing recording without a live connection with a running application.
As Azul Mission Control is Azul's preferred tool for analyzing events within Java applications, we expanded the documentation in docs.azul.com to provide more information about "all things JFR."
This article summarizes that information with direct links to learn more.
Making a Recording
Azul Mission Control provides you insights into your Java application based on recordings. These can be made as files for later analysis or with live insights into a running application.
Recording at the Start of the Application to a File
To recording at the start of the application, you can configure the startup of your application with an additional command:
java -XX:StartFlightRecording=filename=/tmp/rec.jfr,duration=180s -jar my_app.jar
More information: https://docs.azul.com/azul-mission-control/recording/jfr-recording-at-startup
Recording a Running Application to a File
Use the jcmd tool to start the recording of a running application:
jcmd JVMID JFR.start filename=rec.jfr
More information: https://docs.azul.com/azul-mission-control/recording/jfr-recording-during-run
Recording a Running Application with Azul Mission Control
When the JVM is configured to allow remote JMX connections, you can connect directly from Azul Mission Control to make a recording.
More information: https://docs.azul.com/azul-mission-control/recording/jfr-recording-with-amc
Docker Specific Info
As Docker is a "closed environment," creating a JFR recording of an application running in a Docker or Kubernetes environment can be challenging. You can use different approaches, depending on your available connections and where you can store the recording:
- Configure the application to start a recording from startup to a local file or on a volume.
- Use
docker execorkubectl execto start a recording in the container to a local file or on a volume. - Connect directly with Azul Mission Control if the required ports of the container are accessible and JMX has been configured.
More information: https://docs.azul.com/azul-mission-control/recording/jfr-recording-in-docker
Analyze a Recording with Azul Mission Control
When a recording is finished in Azul Mission Control, or a pre-recorded file is opened, an automated analysis result is shown:
The overview screen displays recorded data split into categories. Click a node to investigate the corresponding category details.
- Java Application: Includes data about the recorded Java program workflow: threads life cycle, I/O activity, Exceptions thrown, etc.
- JVM Internals: Holds JVM activity metrics: Class loading, Garbage collection indices, and other events.
- Environment: Holds data about the environment where the JVM runs.
- Event Browser: Displays all the JVM recorded events as a tree.
More information: https://docs.azul.com/azul-mission-control/analyzing/introduction
Conclusion
Thanks to the possibilities of recording to a file with JFR or making a remote connection through JMX, you can tailor a solution that fits your use case and how your Java applications are deployed.
With Azul Mission Control, you can delve deep into the recordings to optimize your code and ensure it runs smoothly and error-free.
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A Closer Look at JFR Streaming
Since JDK 14, there is a new kid on the block – Java Flight Recorder streaming, which enables developers to subscribe to JFR data.
It is a feature allowing a developer to subscribe to select JFR data and to decide what to do with that data in the host process. JFR events can also be consumed from a separate process by pointing to the file repo of a separate JVM process – the mechanism is the same.
Read More
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Analyze JFR Recordings
Continuing from part 1, to exploit the recording by analyzing it, we have a tool named jfr that ships with the JDK. On Linux the alternative jdk management may not be aware of jfr, which means you may need to use the full path to this executable.
The first interesting thing to do is to get an overview of the recording, the summary sub-command displays an histogram of the events.
Read More
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Control JFR Programmatically
While from JDK 14 events can be consumed on the fly, previous JDK versions (from JDK 11) offer a public API useful enough to control Flight Recorder programmatically or to read events from a JFR file.
Such API facilities are useful especially when combined with other technologies like Spring Actuators. Yet when there’s available integration or when using these integrations is too late, like recording startup, the most actionable way to get recording is from the command line.
Read More