JVM Metrics

How are Metrics Calculated?

In Trace0, JVM metrics come from the following two OpenTelemetry sources:

Requests metrics are calculated from the service’s SPAN_KIND_SERVER spans, one per request the service handles. Request count, requests per second, latency percentiles and errors are all derived from these spans and their durations and statuses.
JVM metrics (Memory, Garbage Collection, Threads, Buffers, Classes, CPU and File Descriptors) are calculated from the OpenTelemetry metrics the JVM reports, as defined by the OpenTelemetry semantic conventions for JVM metrics. Each metric below links to its section of that spec.

Aggregation Temporality

OpenTelemetry Sum metrics (Counters and UpDownCounters) and Histogram metrics are reported with an aggregation temporality, which decides what each reported data point means. We use the most recent aggregation temporality the service reported for the metric in the selected period. An aggregation temporality can either be Cumulative or Delta.

Metric Type	Cumulative	Delta
`Sum (Counter, UpDownCounter)`	Each data point is a running total since the process started. We show the most recent value reported in each interval.	Each data point is the change since the previous export. We add up the values reported in each interval.
`Histogram`	Each data point holds each bucket’s running total since the process started. We show each bucket’s most recent count in the selected period.	Each data point holds each bucket’s count since the previous export. We add up each bucket’s counts across the selected period.

Gauge and Summary metrics don’t have an aggregation temporality, so this doesn’t apply to them.

Metrics

We currently display the following application metrics for the JVM:

Requests

Single Value

Metric	Unit	How is it Calculated?
Request Count	Number	TODO
Requests per Second	Number	TODO
Request Latency P99	Time (ms, s)	TODO
Error Rate	Percentage	TODO

Chart

Metric	Description	Chart Type	How is it Calculated?
Request Latency P99, P95, P90, P75, P50	Latency percentile distribution	Line chart	TODO
Requests & Errors	Request volume vs error volume	Histogram	TODO
Errors	Error volume over time	Histogram	TODO
Requests By Endpoint	Request details (count, latency, errors) per endpoint.	Table, one row per endpoint	TODO

JVM Memory

Metric	Description	Chart Type	How is it Calculated?
Total Heap Memory Used	Total memory used (in bytes) across all heap memory pools.	Line chart	From the `jvm.memory.used` metric. We take the series where `jvm.memory.type` is `heap`, and add up their values across every memory pool at each interval.
Heap Memory Used by Pool	Heap memory used (in bytes), per memory pool.	Line chart, one line per memory pool	From the `jvm.memory.used` metric. Split by the `jvm.memory.pool.name`. Only includes pools where the `jvm.memory.type` attribute is `heap`. Each interval shows the most recent value reported.
Non-Heap Memory Used by Pool	Non-heap memory used (in bytes), per memory pool.	Line chart, one line per memory pool	From the `jvm.memory.used` metric. Split by the `jvm.memory.pool.name`. Only includes pools where the `jvm.memory.type` attribute is `non_heap`. Each interval shows the most recent value reported.
Heap Memory Committed by Pool	Memory committed (in bytes), per memory pool.	Line chart, one line per memory pool	From the `jvm.memory.committed` UpDownCounter, obtained from `MemoryPoolMXBean#getUsage()`. Split by the `jvm.memory.pool.name` and `jvm.memory.type` attributes. Each interval shows the most recent value reported.
Memory Limit	Maximum memory (in bytes) that can be obtained, per memory pool.	Line chart, one line per memory pool	From the `jvm.memory.limit` UpDownCounter, obtained from `MemoryPoolMXBean#getUsage()`. Split by the `jvm.memory.pool.name` and `jvm.memory.type` attributes. Each interval shows the most recent value reported.
Memory Used After Last GC	Memory used (in bytes) after the most recent garbage collection on each memory pool.	Line chart, one line per memory pool	From the `jvm.memory.used_after_last_gc` UpDownCounter, obtained from `MemoryPoolMXBean#getCollectionUsage()`. Split by the `jvm.memory.pool.name` and `jvm.memory.type` attributes. Each interval shows the most recent value reported.
Memory Init	Initial memory requested (in bytes), per memory pool.	Line chart, one line per memory pool	From the `jvm.memory.init` UpDownCounter (Development status), obtained from `MemoryPoolMXBean#getUsage()`. Split by the `jvm.memory.pool.name` and `jvm.memory.type` attributes. Each interval shows the most recent value reported.

JVM Garbage Collection

Metric	Description	Chart Type	How is it Calculated?
GC Duration	Distribution of how long (in seconds) garbage collection actions take, per garbage collector.	OpenTelemetry histogram, one per garbage collector	From the `jvm.gc.duration` Histogram. Its values come from `GcInfo#getDuration()` on `GarbageCollectionNotificationInfo` events. Split by the `jvm.gc.name` attribute (e.g. `G1 Young Generation`, `G1 Old Generation`). For each bucket, we add up the counts across the whole selected period. The spec recommends the bucket boundaries `[0.01, 0.1, 1, 10]`.

JVM Threads

Metric	Description	Chart Type	How is it Calculated?
Thread Count	Number of executing platform threads, per thread state.	Line chart, one line per thread state	From the `jvm.thread.count` UpDownCounter, obtained from `ThreadMXBean` / `ThreadInfo#getThreadState()`. Split by the `jvm.thread.state` attribute (e.g. `runnable`, `blocked`, `waiting`, `timed_waiting`). Each interval shows the most recent value reported.

JVM Buffers

Metric	Description	Chart Type	How is it Calculated?
Buffer Memory Used	Memory used by buffers (in bytes), per buffer pool.	Line chart, one line per buffer pool	From the `jvm.buffer.memory.used` UpDownCounter (Development status), obtained from `BufferPoolMXBean#getMemoryUsed()`. Split by the `jvm.buffer.pool.name` attribute (e.g. `mapped`, `direct`). Each interval shows the most recent value reported.
Buffer Memory Limit	Total memory capacity of buffers (in bytes), per buffer pool.	Line chart, one line per buffer pool	From the `jvm.buffer.memory.limit` UpDownCounter (Development status), obtained from `BufferPoolMXBean#getTotalCapacity()`. Split by the `jvm.buffer.pool.name` attribute. Each interval shows the most recent value reported.
Buffer Count	Number of buffers, per buffer pool.	Line chart, one line per buffer pool	From the `jvm.buffer.count` UpDownCounter (Development status), obtained from `BufferPoolMXBean#getCount()`. Split by the `jvm.buffer.pool.name` attribute. Each interval shows the most recent value reported.

JVM Classes

Metric	Description	Chart Type	How is it Calculated?
Classes Loaded	Number of classes loaded since the JVM started.	Line chart	From the `jvm.class.loaded` Counter, obtained from `ClassLoadingMXBean#getTotalLoadedClassCount()`. Each interval shows the most recent value reported (cumulative), or the sum of the values reported during the interval (delta).
Classes Unloaded	Number of classes unloaded since the JVM started.	Line chart	From the `jvm.class.unloaded` Counter, obtained from `ClassLoadingMXBean#getUnloadedClassCount()`. Each interval shows the most recent value reported (cumulative), or the sum of the values reported during the interval (delta).
Class Count	Number of classes currently loaded.	Line chart	From the `jvm.class.count` UpDownCounter, obtained from `ClassLoadingMXBean#getLoadedClassCount()`. Each interval shows the most recent value reported.

JVM CPU

Metric	Description	Chart Type	How is it Calculated?
CPU Time	CPU time used by the process (in seconds), as reported by the JVM.	Line chart	From the `jvm.cpu.time` Counter. It is obtained from `OperatingSystemMXBean#getProcessCpuTime()` on HotSpot and OpenJ9. Each interval shows the most recent value reported (cumulative), or the sum of the values reported during the interval (delta).
CPU Count	Number of processors available to the JVM.	Line chart	From the `jvm.cpu.count` UpDownCounter, obtained from `Runtime#availableProcessors()`. It’s always a whole number, since fractional cores and millicores aren’t represented. Each interval shows the most recent value reported.

JVM File Descriptors

Metric	Description	Chart Type	How is it Calculated?
File Descriptor Count	Number of open file descriptors, as reported by the JVM.	Line chart	From the `jvm.file_descriptor.count` UpDownCounter (Development status, Opt-In), obtained from `UnixOperatingSystemMXBean#getOpenFileDescriptorCount()`. Each interval shows the most recent value reported.
File Descriptor Limit	Maximum number of open file descriptors, as reported by the JVM.	Line chart	From the `jvm.file_descriptor.limit` UpDownCounter (Development status, Opt-In), obtained from `UnixOperatingSystemMXBean#getMaxFileDescriptorCount()`. Each interval shows the most recent value reported.

Introduction

Getting Started

Platform

Agents

Setup Guides

Pricing

Security

FAQ

How are Metrics Calculated?

Aggregation Temporality

Metrics

Requests

JVM Memory

JVM Garbage Collection

JVM Threads

JVM Buffers

JVM Classes

JVM CPU

JVM File Descriptors

​How are Metrics Calculated?

​Aggregation Temporality

​Metrics

​Requests

​JVM Memory

​JVM Garbage Collection

​JVM Threads

​JVM Buffers

​JVM Classes

​JVM CPU

​JVM File Descriptors

How are Metrics Calculated?

Aggregation Temporality

Metrics

Requests

JVM Memory

JVM Garbage Collection

JVM Threads

JVM Buffers

JVM Classes

JVM CPU

JVM File Descriptors