Analyzing Your Application With JFR
Java Flight Recorder (JFR) is a profiling and event collection framework built into the Java Virtual Machine (JVM). With JFR, you can collect detailed runtime information about various aspects of a Java application, such as method execution, memory allocation, garbage collection, and more. This information is valuable for performance analysis, troubleshooting, and optimization of Java applications.
Making a JFR Recording
At Application Startup
To enable recording from startup of an application, use the following command-line option:
-XX:StartFlightRecording=filename=rec.jfr,duration=60s,settings=profile
-
filename=/tmp/rec.jfr: The file that is used to store the recording. -
duration=600s: Specifies the maximum duration for a flight recording. It determines how long the recording continues capturing events and metrics before automatically stopping. You can use this option to limit the duration of a recording to avoid capturing an excessive amount of data and to control the impact on the application’s performance. -
settings=profile: By default, Flight Recorder uses the settings defined in<java_home>/lib/jfr/default.jfcwhich gives a good balance between data and performance. In the same directory, you can find a second configurationprofile.jfcwhich records more events and is useful while profiling an application. You can also create a copy of one these files and create your own configuration, e.g.my-config.jfc.
Check JFR Command Line Options in the documentation of Azul Mission Control for all available options and more info.
From a Running Application
On the same host and userid as the Java process under analysis, run the following command to start a recording:
$ jcmd JVMID JFR.start filename=rec.jfr
Where JVMID is either the process ID or the classname assigned with the java process as shown when running jcmd without parameters.
To stop a recording, use:
$ jcmd JVMID JFR.stop name=1
To start a recording with more detailed metrics, use the following with extra options as explained above:
$ jcmd JVMID JFR.start filename=rec.jfr settings=profile
Analyzing a JFR Recording
JFR recordings are most easily viewed in Azul Mission Control, and you can connect to a running application from within Azul Mission Control to create a recording. More info is available in the Azul Mission Control documentation.