OutOfMemoryError: GC Overhead Limit Exceeded

Why This Happens

This error means the JVM is spending almost all its time doing garbage collection but recovering almost no memory. This typically indicates that the heap is nearly full with live objects that cannot be collected, usually due to a memory leak or processing a dataset too large for the allocated heap.

The Problem

Map<String, String> cache = new HashMap<>();
for (int i = 0; i < 10_000_000; i++) {
    cache.put("key" + i, "value" + i); // Unbounded cache growth
}

The Fix

// Use a bounded cache with LRU eviction
Map<String, String> cache = new LinkedHashMap<>(1000, 0.75f, true) {
    @Override
    protected boolean removeEldestEntry(Map.Entry eldest) {
        return size() > 1000;
    }
};

Step-by-Step Fix

1. 1

   Identify memory-heavy objects

   Take a heap dump and analyze it with Eclipse MAT or VisualVM to find the largest object groups.

2. 2

   Find the retention path

   Trace the GC roots to find why large objects cannot be collected.

3. 3

   Fix the leak or bound the data

   Use bounded caches, process data in streams, close resources properly, or increase heap size with -Xmx.