JVM Metrics

ZIO has built-in support for collecting JVM Metrics. These metrics are a direct port of the JVM metrics provided by the Prometheus Java Hotspot library and compatible with that library.

There are five categories of JVM metrics. Let's look at them one by one:

• Buffer Pools
  • jvm_buffer_pool_used_bytes — Used bytes of a given JVM buffer pool.
  • jvm_buffer_pool_capacity_bytes — Bytes capacity of a given JVM buffer pool.
  • jvm_buffer_pool_used_buffers — Used buffers of a given JVM buffer pool.
• Class Loading
  • jvm_classes_loaded — The number of classes that are currently loaded in the JVM
  • jvm_classes_loaded_total — The total number of classes that have been loaded since the JVM has started execution
  • jvm_classes_unloaded_total — The total number of classes that have been unloaded since the JVM has started execution
• Garbage Collector
  • jvm_gc_collection_seconds_sum — Time spent in a given JVM garbage collector in seconds.
  • jvm_gc_collection_seconds_count
• Memory Allocation
  • jvm_memory_pool_allocated_bytes_total — Total bytes allocated in a given JVM memory pool. Only updated after GC, not continuously.
• Memory Pools
  • jvm_memory_bytes_used — Used bytes of a given JVM memory area.
  • jvm_memory_bytes_committed — Committed (bytes) of a given JVM memory area.
  • jvm_memory_bytes_max — Max (bytes) of a given JVM memory area.
  • jvm_memory_bytes_init — Initial bytes of a given JVM memory area.
  • jvm_memory_pool_bytes_used — Used bytes of a given JVM memory pool.
  • jvm_memory_pool_bytes_committed — Committed bytes of a given JVM memory pool.
  • jvm_memory_pool_bytes_max — Max bytes of a given JVM memory pool.
  • jvm_memory_pool_bytes_init — Initial bytes of a given JVM memory pool.
• Standard
  • process_cpu_seconds_total — Total user and system CPU time spent in seconds.
  • process_start_time_seconds — Start time of the process since unix epoch in seconds.
  • process_open_fds — Number of open file descriptors.
  • process_max_fds — Maximum number of open file descriptors.
  • process_virtual_memory_bytes — Virtual memory size in bytes.
  • process_resident_memory_bytes — Resident memory size in bytes.
• Thread
  • jvm_threads_current — Current thread count of a JVM.
  • jvm_threads_daemon — Daemon thread count of a JVM.
  • jvm_threads_peak — Peak thread count of a JVM.
  • jvm_threads_started_total — Started thread count of a JVM.
  • jvm_threads_deadlocked — Cycles of JVM-threads that are in deadlock waiting to acquire object monitors or ownable synchronizers.
  • jvm_threads_deadlocked_monitor — Cycles of JVM-threads that are in deadlock waiting to acquire object monitors.
  • jvm_threads_state — Current count of threads by state.
• Version Info
  • jvm_info
    • version — java.runtime.version
    • vendor — java.vm.vendor
    • runtime — java.runtime.name

Collecting Metrics

Collecting Inside a ZIO Application

JVM Metrics are collection of the following ZIO services:

• BufferPools
• ClassLoading
• GarbageCollector
• MemoryAllocation
• MemoryPools
• Standard
• Thread
• VersionInfo

All of these services are available in the zio.metrics.jvm package. Each service has a live implementation that can be used to collect metrics, or we can use all of them at once with by providing DefaultJvmMetrics.live layer to our application.

Collecting as a Sidecar to a ZIO Application

ZIO JVM metrics have built-in applications that collect the JVM metrics. They can be composed with other ZIO applications as a sidecar. By doing so, we are able to collect JVM metrics without modifying our main ZIO application. They will be executed as a daemon alongside the main app:

examples/jvm/src/main/scala/zio/examples/metrics/JvmMetricAppExample.scala

package zio.examples.metrics

import zio._
import zio.http._
import zio.metrics.connectors.prometheus.PrometheusPublisher
import zio.metrics.connectors.{MetricsConfig, prometheus}
import zio.metrics.jvm.DefaultJvmMetrics

object JvmMetricAppExample extends ZIOAppDefault {
  private val httpApp =
    Routes(
      Method.GET / "metrics" ->
        handler(ZIO.serviceWithZIO[PrometheusPublisher](_.get.map(Response.text)))
    )

  override def run = Server
    .serve(httpApp)
    .provide(
      // ZIO Http default server layer, default port: 8080
      Server.default,

      // The prometheus reporting layer
      prometheus.prometheusLayer,
      prometheus.publisherLayer,
      // Interval for polling metrics
      ZLayer.succeed(MetricsConfig(5.seconds)),

      // Default JVM Metrics
      DefaultJvmMetrics.liveV2.unit
    )
}