Application Real-Time Monitoring Service:JVM metrics

Memory metrics

The ARMS agent periodically calls ManagementFactory.getPlatformMXBeans(MemoryPoolMXBean.class) to retrieve memory usage for each JVM memory pool.

Each MemoryPoolMXBean reports the initial, maximum, committed, and used sizes for a specific memory space. To query these values directly:

public static void printCurrentJVMMemoryUsage() {
    List<MemoryPoolMXBean> beans = ManagementFactory.getPlatformMXBeans(MemoryPoolMXBean.class);
    for (MemoryPoolMXBean bean : beans) {
        System.out.printf("area=%s\tname=%s\tinitial=%d\tmax=%d\tcommited=%d\tuse=%d\n", bean.getType().name(),
                bean.getName(), bean.getUsage().getInit(), bean.getUsage().getMax(), bean.getUsage().getCommitted(), bean.getUsage().getUsed());
    }
}

Sample output (varies by JVM version):

area=NON_HEAP	name=Code Cache	initial=2555904	max=134217728	commited=3211264	use=3139712
area=NON_HEAP	name=Metaspace	initial=0	max=-1	commited=8388608	use=7950584
area=NON_HEAP	name=Compressed Class Space	initial=0	max=1073741824	commited=1048576	use=919408
area=HEAP	name=PS Eden Space	initial=67108864	max=1409286144	commited=67108864	use=39057856
area=HEAP	name=PS Survivor Space	initial=11010048	max=11010048	commited=11010048	use=0
area=HEAP	name=PS Old Gen	initial=179306496	max=2863661056	commited=179306496	use=0

The agent reports these values directly without additional processing.

GC metrics

The collection method depends on your agent version:

• Before V4.4.0: A scheduled task polls ManagementFactory.getPlatformMXBeans(GarbageCollectorMXBean.class).

• V4.4.0 and later: The agent subscribes to GarbageCollectionNotificationInfo events for real-time collection.

Each GarbageCollectorMXBean reports cumulative GC counts and durations since JVM startup. To query these values directly:

public static void printGC() {
    List<GarbageCollectorMXBean> beans = ManagementFactory.getPlatformMXBeans(GarbageCollectorMXBean.class);
    for (GarbageCollectorMXBean  bean : beans) {
        System.out.printf("name=%s\tgcCount=%d\tgcTime=%d\n", bean.getName(),
                bean.getCollectionCount(), bean.getCollectionTime());
    }
}

Sample output (varies by JVM version):

name=PS Scavenge	gcCount=0	gcTime=0
name=PS MarkSweep	gcCount=0	gcTime=0

Because these values are cumulative since JVM startup, the agent computes the delta between consecutive collections (default interval: 15 seconds). It reports per-interval counts and durations.

Thread stack usage chart

The ARMS console displays a Thread Stack Usage chart. The agent does not collect this metric. Instead, the value equals the current live thread count multiplied by 1 MB. This is the default per-thread stack size the JVM allocates for local variable tables, operand stacks, dynamic links, and method return addresses.

Thread metrics

The ARMS agent periodically calls ManagementFactory.getThreadMXBean() to retrieve thread counts.

The returned ThreadMXBean instance provides the cumulative started thread count, current live thread count, and daemon thread count. The agent also counts live threads by state: RUNNABLE, BLOCKED, WAITING, and TIMED_WAITING.

To query these values directly:

public static void printThreads() {
    ThreadMXBean threadMXBean = java.lang.management.ManagementFactory.getThreadMXBean();
    int threadCount = threadMXBean.getThreadCount();
    int daemonThreadCount = threadMXBean.getDaemonThreadCount();
    long totalStartedThreadCount = threadMXBean.getTotalStartedThreadCount();
    long terminatedThreadCount = totalStartedThreadCount - threadCount;
    System.out.printf("allStartedThreadCount=%d\tcurrentThreadCount=%d\tdaemonThreadCount=%d\tterminatedThreadCount=%d\n"
            , totalStartedThreadCount, threadCount, daemonThreadCount, terminatedThreadCount);
}

Sample output (varies by JVM version):

allStartedThreadCount=5	currentThreadCount=5	daemonThreadCount=4	terminatedThreadCount=0

The terminated thread count equals the cumulative started count minus the current live count. All other values come directly from ThreadMXBean. The agent reports these values without additional processing.

Class loading metrics

The ARMS agent periodically calls ManagementFactory.getClassLoadingMXBean() to retrieve class loading counts.

The returned ClassLoadingMXBean provides cumulative loaded and unloaded class counts since JVM startup. To query these values directly:

public static void printCurrentJVMMemoryUsage() {
    ClassLoadingMXBean classLoaderMXBean = ManagementFactory.getClassLoadingMXBean();
    long totalLoadedClassCount = classLoaderMXBean.getTotalLoadedClassCount();
    long unloadedClassCount = classLoaderMXBean.getUnloadedClassCount();
    System.out.printf("totalLoadedClassCount=%d\tunloadedClassCount=%d\n"
            , totalLoadedClassCount, unloadedClassCount);
}

Sample output (varies by JVM version):

totalLoadedClassCount=1355	unloadedClassCount=0

Because these values are cumulative since JVM startup, the agent computes the delta between consecutive collections (default interval: 15 seconds) to report per-interval counts.

File descriptor metrics

The ARMS agent periodically calls ManagementFactory.getOperatingSystemMXBean() to retrieve file descriptor usage. This metric is available only on Unix-based systems, where the bean is an instance of UnixOperatingSystemMXBean.

To query these values directly:

public static void printFDUsage() {
    OperatingSystemMXBean operatingSystemMXBean = ManagementFactory.getOperatingSystemMXBean();
    if (!(operatingSystemMXBean instanceof UnixOperatingSystemMXBean)) {
        return;
    }
    long openFDCount = ((UnixOperatingSystemMXBean) operatingSystemMXBean).getOpenFileDescriptorCount();
    long maxFDCount = ((UnixOperatingSystemMXBean) operatingSystemMXBean).getMaxFileDescriptorCount();
    System.out.printf("openFDCount=%d\tfdOpenRatio=%f\n"
            , openFDCount, (double) openFDCount / maxFDCount);
}

Sample output (varies by JVM version):

openFDCount=184	fdOpenRatio=0.017969

The open ratio is calculated as openFileDescriptorCount / maxFileDescriptorCount. The agent reports these values without additional processing.