[P2] Add performance benchmarks (JMH)

[sfloess]

Problem

No performance benchmarks exist to measure and track performance characteristics.

Impact

• Severity: MEDIUM
• Category: Performance/Quality
• Unknown performance characteristics
• Cannot detect performance regressions
• No data for optimization decisions
• Difficult to compare with alternatives

Key Performance Metrics Needed

1. Application Lifecycle

• Application startup time: Deploy → Start (warm JVM)
• Application cold start: Deploy → Start (cold JVM)
• Application shutdown time: Stop → Undeploy
• Hot reload latency: Old version → New version

2. ClassLoader Operations

• ClassLoader creation overhead
• Class loading time (first load vs cached)
• ClassLoader cleanup/GC impact

3. Resource Monitoring

• Monitoring overhead (CPU impact of monitoring itself)
• Snapshot collection latency
• Metrics aggregation performance

4. Message Bus

• Publish latency (message → delivered)
• Throughput (messages/second)
• Subscriber overhead (N subscribers impact)

5. REST API

• Deploy endpoint latency
• List applications latency (N apps)
• Concurrent request handling

Recommended Framework

Use JMH (Java Microbenchmark Harness):

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@State(Scope.Benchmark)
public class ApplicationLifecycleBenchmark {
    
    private ApplicationManager manager;
    
    @Setup
    public void setup() {
        manager = new ApplicationManager();
    }
    
    @Benchmark
    public void measureApplicationStartup() {
        manager.deploy(descriptor);
        manager.start("test-app");
    }
}

Module Structure

Create new module:

jplatform-benchmarks/
├── pom.xml (JMH dependencies)
└── src/main/java/
    └── org/flossware/jplatform/benchmarks/
        ├── ApplicationLifecycleBenchmark.java
        ├── ClassLoaderBenchmark.java
        ├── MessageBusBenchmark.java
        └── ResourceMonitorBenchmark.java

Running Benchmarks

mvn clean install -pl jplatform-benchmarks
java -jar jplatform-benchmarks/target/benchmarks.jar

CI/CD Integration

Run benchmarks on release and track trends:

- name: Run Performance Benchmarks
  run: mvn -pl jplatform-benchmarks jmh:run -Djmh.resultFormat=JSON
  
- name: Store Benchmark Results
  uses: benchmark-action/github-action-benchmark@v1
  with:
    tool: 'jmh'
    output-file-path: jplatform-benchmarks/target/jmh-result.json

Performance Targets

Set baselines (example):

• Application startup: < 100ms (warm JVM)
• Message bus publish: < 1ms (p99)
• ClassLoader creation: < 50ms
• REST API deploy: < 200ms

Priority

P2 - Medium - Should be added for v1.3 or v2.0.

Resources

• JMH: https://github.com/openjdk/jmh
• JMH Samples: https://github.com/openjdk/jmh/tree/master/jmh-samples