java.lang.OutOfMemoryError: GC overhead limit exceeded

Introduction

The java.lang.OutOfMemoryError: GC overhead limit exceeded error is a common issue that Java developers encounter when their applications consume too much CPU time on garbage collection with little memory reclaimed. The Java Virtual Machine (JVM) triggers this error when it spends over 98% of the total execution time on garbage collection but reclaims less than 2% of the heap memory during that period.

Understanding how the JVM handles garbage collection and memory allocation is crucial for maintaining high-performing Java applications.

In this article, I'll explore the causes of the java.lang.OutOfMemoryError: GC overhead limit exceeded error, how to diagnose and fix it, and best practices to avoid it in the future.

What causes the OutOfMemoryError: GC overhead limit exceeded error?

The java.lang.OutOfMemoryError: GC overhead limit exceeded error occurs when the JVM spends too much time performing garbage collection and recovers too little memory.

This error is typically caused by one of the following reasons:

1. Memory Leak: Your application may have a memory leak, causing it to consume more memory than necessary.
2. Inefficient Code: Your application may be inefficiently using memory, leading to excessive garbage collection.
3. Large Heap Size: If your application has a large heap size, garbage collection may take longer to complete.
4. Inadequate Heap Size: If your application has an inadequate heap size, garbage collection may not be able to reclaim enough memory.

The following code snippet shows an example of a memory leak that can lead to the java.lang.OutOfMemoryError: GC overhead limit exceeded error:

import java.util.ArrayList;
import java.util.List;

public class MemoryLeak {

  // List to store Long objects
  private static final List<Long> longs = new ArrayList<>();

  public static void main(String[] args) {
    // Infinite loop to add Long.MAX_VALUE to the list
    while (true) {
      longs.add(Long.MAX_VALUE);
    }
  }
}

In this example, Long.MAX_VALUE is repeatedly added to the list, simulating unbounded memory growth. The list's persistent reference prevents garbage collection from reclaiming memory.

If we execute the MemoryLeak class with the following command:

java -Xmx10m -XX:+UseParallelGC MemoryLeak.java

The Xmx flag sets the maximum heap size to 10MB, and the UseParallelGC flag specifies the Parallel Garbage Collector. Since the MemoryLeak class adds Long.MAX_VALUE to the longs list in an infinite loop, the list will grow indefinitely. The garbage collector will try to reclaim memory, but since the list is still growing and referenced by the main class, it will spend most of its time doing garbage collection with little memory reclaimed.

The JVM will eventually (and quickly) run out of memory and throw the java.lang.OutOfMemoryError: GC overhead limit exceeded error:

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
        at java.base/java.lang.Long.valueOf(Long.java:1204)
        at MemoryLeak.main(MemoryLeak.java:9)
        at java.base/java.lang.invoke.LambdaForm$DMH/0x00007fab38030000.invokeStatic(LambdaForm$DMH)
        at java.base/java.lang.invoke.LambdaForm$MH/0x00007fab3813d400.invoke(LambdaForm$MH)
        at java.base/java.lang.invoke.Invokers$Holder.invokeExact_MT(Invokers$Holder)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invokeImpl(DirectMethodHandleAccessor.java:154)

How to diagnose and fix the OutOfMemoryError: GC overhead limit exceeded error?

To diagnose and fix the java.lang.OutOfMemoryError: GC overhead limit exceeded error, follow these steps:

1. Analyze Heap Dumps: Use a heap dump analysis tool like VisualVM, JProfiler, or YourKit to identify memory leaks and inefficient memory usage.
2. Optimize Code: Identify and fix memory leaks, such as unintentional object retention in collections, and ensure efficient use of memory-intensive operations like caching or object creation.
3. Tune Garbage Collection:
   • Adjust the garbage collection settings to optimize memory usage and reduce garbage collection overhead.
   • Consider using a different garbage collector, such as the G1 Garbage Collector (-XX:+UseG1GC), which is designed for large heaps and low-latency applications.
4. Increase Heap Size: If your application is running out of memory, consider increasing the heap size to allow more memory for garbage collection.

Your process should make sure that the root cause of the OutOfMemoryError is not a memory leak or inefficient memory usage. Once and only when you've ensured the heap usage is optimal and genuine, you can adjust the garbage collection settings or increase the heap size to avoid the error.

Conclusion

The java.lang.OutOfMemoryError: GC overhead limit exceeded error is a common issue in Java applications that consume too much CPU time on garbage collection. Diagnosing and fixing this error involves identifying the root cause through heap dump analysis, resolving memory inefficiencies, and tuning JVM settings to optimize garbage collection and memory allocation. By following these best practices, you can avoid the OutOfMemoryError error and improve the performance and stability of your Java applications.

References

• Stack Overflow: Error java.lang.OutOfMemoryError: GC overhead limit exceeded
• Oracle: HotSpot Virtual Machine Garbage Collection Tuning Guide