GC 알고리즘: Serial, G1, ZGC, Shenandoah

// Enable GC algorithms:
// -XX:+UseSerialGC
// -XX:+UseParallelGC
// -XX:+UseG1GC       (default since Java 9)
// -XX:+UseZGC        (Java 15+ production)
// -XX:+UseShenandoahGC (Red Hat / OpenJDK builds)

// Use:
// java -XX:+UseSerialGC -Xmx256m MyApp
// Pauses: long (proportional to heap size)
// Throughput: low
// Best for: CLI tools, small heaps < 100 MB

// Use:
// java -XX:+UseParallelGC -XX:ParallelGCThreads=8 MyApp
// Pauses: moderate
// Throughput: high
// Best for: batch jobs, number crunching

// Use:
// java -XX:+UseG1GC -XX:MaxGCPauseMillis=200 MyApp
// Pauses: bounded by target (but not guaranteed)
// Throughput: good
// Best for: large heaps (4 GB+), mixed workloads

// Use:
// java -XX:+UseZGC -Xmx16g MyApp
// Pauses: < 1 ms (usually)
// Throughput: slightly lower than G1 (concurrent work has CPU cost)
// Best for: large heaps, low-latency services (APIs, trading)

// Use:
// java -XX:+UseShenandoahGC MyApp
// Available in: Red Hat builds, some AdoptOpenJDK distributions
// Pauses: sub-millisecond
// Best for: latency-sensitive workloads

// Enable in Java 21+:
// java -XX:+UseZGC -XX:+ZGenerational -Xmx8g MyApp

// JVM flags:
// -Xlog:gc*:file=gc.log:time,uptime,level,tags
// Inspect logs:
// cat gc.log | grep "Pause"

ManagementFactory.getGarbageCollectorMXBeans().forEach(gc ->
    System.out.printf("%s: %d collections, %d ms%n",
        gc.getName(), gc.getCollectionCount(), gc.getCollectionTime()));