Modern Java applications often face performance challenges that are difficult to diagnose in production environments. High CPU usage, memory leaks, inefficient garbage collection, and thread contention can degrade performance, leading to sluggish applications and costly downtime. Traditional profilers introduce too much overhead for production use, making them impractical. This is where Java Flight Recorder (JFR) and Java Mission Control (JMC) become invaluable.
These tools allow developers to monitor and diagnose performance issues with minimal impact on application execution. In this article, we’ll explore how JFR and JMC work and walk through a real-world case study demonstrating their effectiveness.
What is Java Flight Recorder (JFR)?
Java Flight Recorder is an efficient, event-based profiling tool built into the Java Virtual Machine (JVM). It collects a wealth of data about an application’s execution with minimal overhead, making it ideal for use in production. JFR captures details such as:
- CPU and memory usage
- Garbage collection (GC) activity
- Thread synchronization and locks
- Method execution times
To start JFR when launching an application, you can use:
1 | java -XX:StartFlightRecording=filename=recording.jfr,duration=60s,settings=profile -jar yourapp.jar |
For running applications, JFR can be dynamically enabled without restarting:
1 | jcmd <pid> JFR.start name=myrecording duration=120s filename=myrecording.jfr |
This allows for on-the-fly monitoring of performance issues, a crucial advantage in production environments.
Java Mission Control (JMC): Analyzing JFR Data
Java Mission Control is the companion tool for JFR, offering a graphical interface to analyze recorded data. JMC provides insights into application behavior, helping developers identify bottlenecks and inefficiencies. Key analysis features include:
- Memory and GC Profiling – Track object allocations and optimize garbage collection.
- Thread Analysis – Identify deadlocks and excessive context switching.
- CPU and Hotspot Detection – Pinpoint methods consuming the most CPU cycles.
By opening a .jfr file in JMC, developers can navigate through these metrics and uncover performance bottlenecks quickly.
Case Study: Diagnosing a Memory Leak in a Java Web Application
Let’s look at how a development team used JFR and JMC to diagnose a memory leak in a production Java web application.
Problem Statement
A financial services company running a Spring Boot application on AWS noticed a steady increase in memory usage. The application eventually crashed due to OutOfMemoryError, despite regular garbage collection. Traditional monitoring tools showed increasing heap usage but couldn’t identify the cause.
Using JFR to Capture Data
The team enabled JFR on the live application without restarting:
1 | jcmd <pid> JFR.start name=memoryleak duration=300s filename=memoryleak.jfr |
After five minutes, they stopped JFR and analyzed the .jfr file in JMC.
Analyzing JFR Data in JMC
In JMC, the Memory & Object Allocation section revealed an unusually high number of ArrayList instances. Further investigation showed that a caching mechanism was incorrectly holding references to old data, preventing garbage collection.
Fixing the Issue
The team updated the caching logic to use WeakReference, ensuring old objects were properly garbage collected. After redeploying the fix, they ran JFR again and confirmed that memory usage remained stable.
Final Thoughts
Java Flight Recorder and Java Mission Control provide powerful yet lightweight profiling capabilities for production applications. Whether diagnosing memory leaks, optimizing CPU usage, or improving garbage collection efficiency, these tools offer actionable insights with minimal impact.
By integrating JFR and JMC into your workflow, you can proactively detect and resolve performance issues, keeping your Java applications running efficiently.
