name	java-performance
description	JVM performance tuning - GC optimization, profiling, memory analysis, benchmarking
sasmp_version	1.3.0
version	3.0.0
bonded_agent	02-java-advanced
bond_type	SECONDARY_BOND
allowed-tools	Read, Write, Bash, Glob, Grep
parameters	{"focus":{"type":"string","enum":["gc","memory","cpu","profiling"],"description":"Performance focus area"}}

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

# 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

# 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

@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

Skill("java-performance")