What JVM memory areas matter to a Java backend service?

Explains heap, per-thread stacks, Metaspace, code cache, and native memory through the failures and evidence they produce.

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The Java heap holds ordinary objects and is managed by the garbage collector. Each thread has a stack containing method frames and local execution state, while class metadata is stored in Metaspace. The JVM also uses native memory for areas such as thread stacks, direct buffers, native libraries, and internal runtime structures. These areas have different limits and produce different symptoms, so an OutOfMemoryError is not automatically a heap leak.

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A practical JVM memory model that avoids the inaccurate shortcut that every value has one fixed physical location.

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Core answer
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The useful distinction is which runtime resource is exhausted or retaining data, not a decorative stack-versus-heap diagram.
The Java heap holds ordinary objects and is managed by the garbage collector. Each thread has a stack containing method frames and local execution state, while class metadata is stored in Metaspace. The JVM also uses native memory for areas such as thread stacks, direct buffers, native libraries, and internal runtime structures. These areas have different limits and produce different symptoms, so an OutOfMemoryError is not automatically a heap leak.
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A deep or unbounded call chain can exhaust a thread stack and produce StackOverflowError. Excessive class loading can exhaust Metaspace, while too many threads or large direct buffers can exhaust native or process memory even when the Java heap looks healthy. Local variables hold values according to Java semantics, but the JVM may optimize object allocation and representation. I explain the observable regions first and use the error detail, process metrics, GC data, and native-memory evidence to locate the failing resource.

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Treating every memory failure as heap exhaustion.
Saying objects always live in one fixed physical location.
Setting heap equal to the full container limit.

What JVM memory areas matter to a Java backend service?

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