How would you diagnose OutOfMemoryError in a Java service?

Triages heap, Metaspace, native, direct-buffer, thread, and container exhaustion using preserved evidence before changing limits.

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TL;DR

First I preserve the exact error detail and surrounding service, container, and GC evidence because Java heap space, Metaspace, direct-buffer failure, native thread creation, and an operating-system kill are different incidents. For heap exhaustion, I want a heap dump near failure plus GC and allocation history. For native or process exhaustion, I inspect RSS, thread count, direct memory, container limits, and native-memory evidence. I stabilize the service separately from diagnosing the cause.

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Production incident response, evidence selection, memory-pool differentiation, and safe verification.

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Core answer
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Overview
The detail message and deployment evidence determine which memory resource failed and which artifact can explain it.
First I preserve the exact error detail and surrounding service, container, and GC evidence because Java heap space, Metaspace, direct-buffer failure, native thread creation, and an operating-system kill are different incidents. For heap exhaustion, I want a heap dump near failure plus GC and allocation history. For native or process exhaustion, I inspect RSS, thread count, direct memory, container limits, and native-memory evidence. I stabilize the service separately from diagnosing the cause.
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Stronger answer
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A rising post-GC live set points toward retention, while a stable live set with very high allocation and GC time points toward allocation pressure or undersized capacity. Metaspace growth can indicate excessive class loading or class-loader retention. An OOM-killed container may leave no Java exception, so platform events and exit codes matter. I avoid taking repeated full dumps on a struggling fleet because dump creation is expensive and the files can be large and sensitive.

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Details

Treating all OOM details as heap leaks.
Collecting disruptive evidence on every instance.
Calling a larger heap a complete fix.

How would you diagnose OutOfMemoryError in a Java service?

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