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Merged
trask merged 2 commits into from
Nov 19, 2025
Merged

List JFR events used in metrics #15332

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List JFR events used in metrics
brunobat Nov 17, 2025
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Merge branch 'main' into jdk-event-docs
laurit Nov 19, 2025
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40 changes: 27 additions & 13 deletions instrumentation/runtime-telemetry/runtime-telemetry-java17/library/README.md
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Expand Up @@ -35,16 +35,30 @@ default, and the telemetry each produces:
<!-- DO NOT MANUALLY EDIT. Regenerate table following changes to instrumentation using ./gradlew generateDocs -->
<!-- generateDocsStart -->

| JfrFeature | Default Enabled | Metrics |
|---------------------------|-----------------|-------------------------------------------------------------------------------------------------------------------|
| BUFFER_METRICS | `false` | `jvm.buffer.count`, `jvm.buffer.memory.limit`, `jvm.buffer.memory.used` |
| CLASS_LOAD_METRICS | `false` | `jvm.class.count`, `jvm.class.loaded`, `jvm.class.unloaded` |
| CONTEXT_SWITCH_METRICS | `true` | `jvm.cpu.context_switch` |
| CPU_COUNT_METRICS | `true` | `jvm.cpu.limit` |
| CPU_UTILIZATION_METRICS | `false` | `jvm.cpu.recent_utilization`, `jvm.system.cpu.utilization` |
| GC_DURATION_METRICS | `false` | `jvm.gc.duration` |
| LOCK_METRICS | `true` | `jvm.cpu.longlock` |
| MEMORY_ALLOCATION_METRICS | `true` | `jvm.memory.allocation` |
| MEMORY_POOL_METRICS | `false` | `jvm.memory.committed`, `jvm.memory.init`, `jvm.memory.limit`, `jvm.memory.used`, `jvm.memory.used_after_last_gc` |
| NETWORK_IO_METRICS | `true` | `jvm.network.io`, `jvm.network.time` |
| THREAD_METRICS | `false` | `jvm.thread.count` |
**Warning**: JFR events might not be available for all JVMs or with a GraalVM native image, therefore limiting the produced metrics. The original implementation was done for Hotspot. OpenJ9 currently (Nov. 2025) only has the VM-level JFR implementation. So events emitted at the Java level (ie. in jdk.jfr) will not be present. Meaning, jdk.SocketRead, jdk.SocketWrite won't work.

| JfrFeature | Jfr Event names | Default Enabled | Metric names |
|---------------------------|----------------------------------------------------------------------------------------------|-----------------|-------------------------------------------------------------------------------------------------------------------|
| BUFFER_METRICS | `jdk.DirectBufferStatistics`[6] | `false` | `jvm.buffer.count`, `jvm.buffer.memory.limit`, `jvm.buffer.memory.used` |
| CLASS_LOAD_METRICS | `jdk.ClassLoadingStatistics`[5] | `false` | `jvm.class.count`, `jvm.class.loaded`, `jvm.class.unloaded` |
| CONTEXT_SWITCH_METRICS | `jdk.ThreadContextSwitchRate`[6] | `true` | `jvm.cpu.context_switch` |
| CPU_COUNT_METRICS | `jdk.ContainerConfiguration` | `true` | `jvm.cpu.limit` |
| CPU_UTILIZATION_METRICS | `jdk.CPULoad`[6] | `false` | `jvm.cpu.recent_utilization`, `jvm.system.cpu.utilization` |
| GC_DURATION_METRICS | `jdk.G1GarbageCollection`[1], `jdk.OldGarbageCollection`[4], `jdk.YoungGarbageCollection`[4] | `false` | `jvm.gc.duration` |
| LOCK_METRICS | `jdk.JavaMonitorWait` | `true` | `jvm.cpu.longlock` |
| MEMORY_ALLOCATION_METRICS | `jdk.ObjectAllocationInNewTLAB`, `jdk.ObjectAllocationOutsideTLAB`[2] | `true` | `jvm.memory.allocation` |
| MEMORY_POOL_METRICS | `jdk.G1HeapSummary`[1], `jdk.MetaspaceSummary`[2], `jdk.PSHeapSummary`[3] | `false` | `jvm.memory.committed`, `jvm.memory.init`, `jvm.memory.limit`, `jvm.memory.used`, `jvm.memory.used_after_last_gc` |
| NETWORK_IO_METRICS | `jdk.SocketRead`, `jdk.SocketWrite` | `true` | `jvm.network.io`, `jvm.network.time` |
| THREAD_METRICS | `jdk.JavaThreadStatistics` | `false` | `jvm.thread.count` |

**[1]** - G1 doesn't exist if you use the [community edition](https://www.graalvm.org/community/) for GraalVM native image.

**[2]** - Not applicable for GraalVM native image.

**[3]** - No parallel GC on GraalVM native image.

**[4]** - On GraalVM there is no true "old" and "eden" spaces. Everything is allocated in linked heap chunks.

**[5]** - No dynamic class loading on GraalVM.

**[6]** - Possible but not implemented on GraalVM, as of Nov. 2025.
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