High CPU in "VM Thread" in Java application

Environment

• OpenJDK
• Oracle JDK

Issue

• My Java application is using a lot of CPU time, and there is a single thread called "VM Thread" that is using ~100% cpu. Why is this occurring?

Resolution

Inspect the GC logging and heap dump to determine if the excessive GC is due to an undersized heap or unintended object retention.

Root Cause

The high cpu is due to garbage collection or another JVM operation that requires a safepoint: Deoptimization, PrintThreads, PrintJNI, FindDeadlock, ThreadDump, EnableBiasLocking, RevokeBias, HeapDumper, GetAllStackTrace.

Diagnostic Steps

• Captured thread dumps and top data to see the high CPU usage.
• Request a heap dump and GC logs from the time of the issue.
• Check if a significant amount of stopped time is not GC related.

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