Performance optimization is crucial for building scalable, high-performing Java applications. While traditional profiling tools can introduce significant overhead, Java provides a built-in, low-overhead solution: Java Flight Recorder (JFR).

JFR is a continuous profiling tool that collects detailed runtime metrics, helping developers identify bottlenecks, diagnose issues, and fine-tune JVM performance. In this article, we’ll explore how JFR works, how to enable and configure it, and how to analyze performance data effectively.

What Is Java Flight Recorder?

Overview of JFR

Java Flight Recorder is a built-in JVM profiling tool designed for high-performance applications. It captures low-level system events and JVM statistics, enabling developers to analyze memory, CPU usage, GC behavior, thread activity, and more.

Why Use JFR?

✔ Low Overhead – JFR runs with minimal impact on application performance.
✔ Continuous Monitoring – Unlike traditional profilers, JFR records events over time for better analysis.
✔ Deep JVM Insights – Captures GC logs, thread dumps, method profiling, IO operations, and more.
✔ Integrated with JDK – No need for third-party tools, available in JDK 11+ (free).

Enabling Java Flight Recorder

JFR can be enabled in multiple ways:

1. Enable JFR at JVM Startup

java -XX:StartFlightRecording=name=profile,filename=myrecording.jfr

2. Start JFR Dynamically (Without Restarting JVM)

jcmd <pid> JFR.start name=profile filename=myrecording.jfr

3. Stop and Dump JFR Data

jcmd <pid> JFR.stop name=profile

Analyzing JFR Data

JFR recordings can be analyzed using tools like:

  • JDK Mission Control (JMC) – A GUI tool for visualizing JFR recordings.
  • Command-line Analysis – Use jfr print to inspect event logs.

Example: Viewing JFR Events

jfr print --events cpu,thread myrecording.jfr

Key Metrics Captured by JFR

Metric Insights Provided
CPU Usage Identifies high-CPU-consuming methods and threads
Garbage Collection (GC) Analyzes GC pauses and heap behavior
Thread Activity Detects deadlocks, blocked threads, and latency issues
I/O Operations Monitors disk and network bottlenecks
Memory Allocation Identifies excessive object creation and leaks

Optimizing Performance with JFR

1. Detecting High CPU Usage

Use JFR to find CPU hotspots by analyzing method sampling data:

  • Open JFR in JMC and check “Method Profiling”.
  • Identify methods with the highest CPU time.
  • Optimize inefficient loops or use caching to reduce CPU overhead.

2. Analyzing Garbage Collection (GC) Performance

JFR provides detailed GC logs to detect memory issues:

  • Check GC pauses and heap usage trends.
  • Tune JVM GC parameters for better performance:
java -XX:+UseG1GC -XX:InitiatingHeapOccupancyPercent=45

3. Detecting I/O Bottlenecks

JFR records disk and network activity, helping developers:

  • Identify slow database queries.
  • Optimize disk writes and reads.
  • Reduce unnecessary network calls.

Best Practices for Using JFR

✅ Use JFR in production – It has minimal overhead.
✅ Capture long-running recordings for better insights.
✅ Combine JFR with logs and metrics for full visibility.
✅ Use JMC for visualization to easily identify performance issues.

Conclusion

Java Flight Recorder is an essential tool for advanced JVM profiling and performance tuning. With low overhead, deep runtime insights, and seamless integration, JFR helps developers diagnose bottlenecks, optimize resource usage, and improve application performance.

Key Takeaways:

✔ JFR provides low-cost, continuous profiling for Java applications.
✔ Captures JVM metrics, thread activity, GC performance, and more.
✔ Integrated with JDK Mission Control (JMC) for advanced analysis.
✔ Ideal for diagnosing CPU, memory, and I/O performance issues.

By leveraging Java Flight Recorder, you can fine-tune your Java applications and ensure optimal performance at scale. Ready to start profiling? 🚀