Java Performance Skill
Optimize JVM performance through profiling, GC tuning, and memory analysis.
Overview
This skill covers JVM performance optimization including garbage collection tuning, memory analysis, CPU profiling, and benchmarking with JMH.
When to Use This Skill
Use when you need to:
- •Tune GC for low latency or throughput
- •Profile CPU hotspots
- •Analyze memory leaks
- •Benchmark code performance
- •Optimize container settings
Quick Reference
GC Presets
bash
# High-throughput -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -Xms4g -Xmx4g -XX:+AlwaysPreTouch # Low-latency -XX:+UseZGC -XX:+ZGenerational -Xms8g -Xmx8g # Memory-constrained -XX:+UseSerialGC -Xms512m -Xmx512m -XX:+UseCompressedOops # Container-optimized -XX:+UseContainerSupport -XX:MaxRAMPercentage=75.0 -XX:+ExitOnOutOfMemoryError
Profiling Commands
bash
# Thread dump jstack -l <pid> > threaddump.txt # Heap dump jmap -dump:format=b,file=heap.hprof <pid> # GC analysis jstat -gcutil <pid> 1000 10 # Flight recording jcmd <pid> JFR.start duration=60s filename=app.jfr # Async profiler ./profiler.sh -d 30 -f profile.html <pid>
JMH Benchmark
java
@BenchmarkMode(Mode.Throughput)
@Warmup(iterations = 3, time = 1)
@Measurement(iterations = 5, time = 1)
@State(Scope.Benchmark)
public class MyBenchmark {
@Benchmark
public void testMethod(Blackhole bh) {
bh.consume(compute());
}
}
GC Comparison
| GC | Latency | Throughput | Heap Size |
|---|---|---|---|
| G1 | Medium | High | 4-32GB |
| ZGC | Very Low | Medium | 8GB-16TB |
| Shenandoah | Very Low | Medium | 8GB+ |
| Parallel | High | Very High | Any |
Troubleshooting
| Problem | Cause | Solution |
|---|---|---|
| GC thrashing | Heap too small | Increase heap |
| High latency | GC pauses | Switch to ZGC |
| Memory leak | Object retention | Heap dump + MAT |
| CPU spikes | Hot loops | Profile + optimize |
Usage
code
Skill("java-performance")