Troubleshooting with Java Flight Recorder

background purpose

Let's use Oracle Java Mission Control (JMC) / Java Flight Recorder (JFR), which is a paid monitoring and troubleshooting tool available from Oracle Java7 u40 or later.

What is JMC / JFR?

--Java application monitoring and troubleshooting tool provided by Java SE Advanced, a paid product of Oracle Java. --However, JMC / JFR itself (required binary / mechanism) is already included in the (ordinary) Oracle JDK that can be downloaded free of charge, so it can be used free of charge for verification purposes on a personal PC. In short, the paid product Java SE Advanced offers only usage rights, and the binaries themselves are exactly the same. --So, no special download / installation is required, and you can use it immediately if you have the Oracle JDK installed. ――If you roughly distinguish between JMC and JFR, --JMC is a GUI and simple real-time monitoring, --JFR is a profiler that records the behavior of Java applications (airplane black box --product name after Flight Recorder) ――However, in general, both are called JMC or JFR. --Since the recording (profiling) mechanism itself is included in Oracle's HotSpot JVM, there is little overhead due to recording. --Recording records are output as a file with a ".jfr" extension, so you can analyze this file by viewing it from the JMC GUI. --Originally a feature of jRockIt, a former BEA (acquired by Oracle) JVM, ported by Oracle from Oracle Java7 u40 or later so that it can also be used with the Oracle HotSpot JVM. ――There have been various kinds of diagnostic tools and commands in Java so far, but is Oracle aiming to make it almost covered by JMC / JFR?

Verification environment

--Oracle JDK 8 latest --OS: Windows 7 (Of course, any type of OS can be used as long as the JDK runs)

References

--oracle.com --JMC / JFR --JMC / JFR Official Website --docs.oracle.com --Oracle Commercial Features --JMC / JFR --Official Manual -Marcus Hirt --JMC Tutorial --This is a must! You can understand how to use and analyze JFR based on the sample code. --JavaOne 2016 --Java Mission Control 5.5 --Presentation materials can be downloaded -YouTube --Java Mission Control --JMC / JFR overview video for about 30 minutes -YouTube --Java Mission Control Demo --JMC / JFR demo video of about 10 minutes -docs.oracle.com --Java Platform, Standard Edition Troubleshooting Guide -O'Reilly --Java Performance: The Definitive Guide --Overview of JMC / JFR in "Chapter 3. A Java Performance Toolbox" and other chapters Introducing tuning examples using JFR

Download and install

--JMC / JFR itself is built into the JDK, so if you already have the JDK installed, no additional downloads or installations are required! You can start using it according to the execution method below. --If you want to use Eclipse Plugin, download it from the following site (not required) - [Oracle Java Mission Control for Eclipse] (http://download.oracle.com/technology/products/missioncontrol/updatesites/experimental/5.5.0/eclipse/)

Execution method

--Starting JMC / JFR GUI --Execute $ {JAVA_HOME} \ bin \ jmc.exe --Enable JFR --Just add the following parameters to the JVM startup parameters! - -XX:+UnlockCommercialFeatures -XX:+FlightRecorder --There are three ways to start JFR recording (example of outputting with the name my_recording.jfr). ―― 1. Specified by the startup argument - java.exe -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:StartFlightRecording=duration=60s,filename=my_recording.jfr MyJavaApplication --2 Start with jcmd command - jcmd <PID> JFR.start duration=60s filename=my_recording.jfr ―― 3. Start from JMC GUI (easiest) --Described in the next section

Quickly move what it looks like

1. What to prepare

Download the "Java SE Development Kit 8uXXX Demos and Samples Downloads zip" from the JDK Download Site. Actually, the sample file of jfr is also included in this.

--Location: sample \ missioncontrol \ flightrecordings folder in the above downloaded zip file --Sample file --java2d_demo.jfr: JFR recording sample of demo \ jfc \ Java2D \ Java2Demo.jar in the zip file --wldf.jfr: [WebLogic MedRec Sample](http://www.oracle.com/webfolder/technetwork/tutorials/obe/fmw/wls/12c/12_2_1/02-34-004-DeploySampleApplication/deploysampleapplication.html# JFR recording sample in section 4)

2. Browse the already recorded jfr file

Execute $ {JAVA_HOME} \ bin \ jmc.exe

Select java2d_demo.jfr from File-> Open File ... and open it. Like below If you can see the screen, it's OK.

3. Try to record it yourself

Let's actually record using Java2Demo.jar included in Java Demos and Samples.

Step1. Run the sample app

Execute the Java2Demo.jar file as follows

SET JDK_HOME=<JDK path>
SET PRG=D:\A_Dev\Java\jdk-8u101-windows-x64-demos\jdk1.8.0_101\demo\jfc\Java2D\Java2Demo.jar
SET JVM=-Xmx32m -Xms16m ← To generate GC frequently. Not required
SET JFR=-XX:+UnlockCommercialFeatures -XX:+FlightRecorder

%JDK_HOME%\bin\java %JVM% %JFR% -jar %PRG%

Click here for the screen image of Java2Demo.jar. To load, select the tab "Transforms" and set the Anim delay on the right side of the screen short.

Step2. Start the JMC screen

When you start jmc.exe, the following screen is displayed. You should see the Java2Demo.jar process on the left. The second "The JVM Running Mission Control" process on the left is jmc's own process.

Step3. Flight record from JMC screen

Right-click on the process part and select "Start Flight Recording ...".

From the "Start Flight Recording" screen below, set the recording time to "1 min" and the event setting to "Profiling --on server". Click the "Finish" button to start recording.

The following pop-up will appear and recording will start. While waiting for 1 minute, play around with the Java2Demo.jar app (with or without load).

Step4. Browse the recorded jfr

After 1 minute, the .jfr file that has been recorded automatically should start up.

Confirmation point 1-General

You can see the average and maximum values of "heap usage", "CPU usage", and "GC pause time" recorded for 1 minute as shown below.

Confirmation point 2 --GC

Select the "Memory" main tab on the left and select the "Garbage Collection" subtab. It can be seen that GC occurs frequently as shown below.

Confirmation point 3 --Hot Methods

Select the "Code" main tab on the left and select the "Hot Methods" subtab. You can see that java.util.HashMap.put, java.awt.TexturePaintContext ... was called most often during the 1 minute of recording.

JMC / JFR screen configuration

The overall screen configuration consists of the main tab on the left and the sub-tabs for each main tab. The screen configuration for each main tab is as follows (* The WebLogic main tab in the screen capture is what you see if you have the WebLogic plugin installed)

General

Memory

Code

Thread

I/O

System

Event

List of each main tab / sub tab

(* Below, tab names are written in English. Since most of the various manuals and references are in English, it is easier to get used to them with English names.)