Common Java OutOfMemoryError Types and Their Solutions

When the JVM runs out of memory, it throws a java.lang.OutOfMemoryError. The article summarizes the most common OOM causes and their solutions.

1. Java heap space

Occurs when the heap cannot accommodate new objects, triggering java.lang.OutOfMemoryError: Java heap space. Typical reasons include creating oversized objects, traffic spikes, excessive finalizer usage, and memory leaks (e.g., unclosed resources). The usual fix is to increase the -Xmx heap size, or address the specific cause such as limiting large object creation, adding resources, or fixing leaks.

2. GC overhead limit exceeded

Thrown when the JVM spends >98% of time in GC but recovers <2% of memory repeatedly. The cause and solution are similar to heap space issues: increase heap size or reduce memory pressure.

3. PermGen space (pre‑Java 8)

Indicates the permanent generation is full, often due to loading many or large classes. Solutions include increasing -XX:MaxPermSize, restarting the JVM to clear duplicated classloaders, or enabling class unloading with -XX:+CMSClassUnloadingEnabled and -XX:+UseConcMarkSweepGC. Memory dumps can be analyzed with jmap -dump:format=b,file=dump.hprof <pid> and Eclipse MAT.

4. Metaspace (Java 8+)

Metaspace replaces PermGen; the error java.lang.OutOfMemoryError: Metaspace has similar causes. Adjust its size with -XX:MaxMetaspaceSize.

5. Unable to create new native thread

Occurs when the OS cannot allocate a native thread due to OS limits (ulimit, kernel.pid_max), or insufficient native memory. Solutions: increase OS limits, add memory, reduce thread count, lower stack size with -Xss, and configure thread pools.

6. Out of swap space

All virtual memory is exhausted. Causes include address space shortage, full physical memory, native memory leaks, or large DirectByteBuffer usage. Remedies: move to 64‑bit, check for compression issues, lower -XX:MaxDirectMemorySize, or upgrade hardware.

7. Requested array size exceeds VM limit

The JVM limits array length to Integer.MAX_VALUE-2. Verify whether such large arrays are necessary and split them if possible.

8. Direct buffer memory

Direct ByteBuffer default limit is 64 MB; exceeding it throws java.lang.OutOfMemoryError: Direct buffer memory. Diagnose with tools like Arthas, check NIO usage, adjust -XX:MaxDirectMemorySize, remove -XX:+DisableExplicitGC if present, and ensure proper buffer cleanup.

Recommended Tools & Products

• Eclipse Memory Analyzer (MAT) – https://www.eclipse.org/mat

• Alibaba Cloud APM for OOM keyword alerts – https://help.aliyun.com/document_detail/42966.html

• Alibaba Arthas – https://github.com/alibaba/arthas

For further reading see articles on Plumbr, GCeasy, and JVM memory architecture.