Introduction

Unreal Engine’s garbage collector automatically manages memory by cleaning up unused objects. However, improper object lifecycle management, frequent memory allocations, and unoptimized GC settings can cause performance bottlenecks. This issue is particularly problematic in open-world games, high-asset environments, and VR applications where memory usage is high. This article explores the causes, debugging techniques, and solutions to optimize garbage collection performance in Unreal Engine.

Common Causes of Garbage Collection Issues in Unreal Engine

1. Excessive Actor Spawning Without Proper Cleanup

Spawning actors dynamically without destroying them properly leads to memory leaks and increased GC workload.

Problematic Code

for (int i = 0; i < 1000; i++) {
    GetWorld()->SpawnActor(EnemyClass, SpawnLocation, SpawnRotation);
}

Solution: Destroy Unused Actors Efficiently

TArray Enemies;
UGameplayStatics::GetAllActorsOfClass(GetWorld(), AEnemyCharacter::StaticClass(), Enemies);
for (AActor* Enemy : Enemies) {
    Enemy->Destroy();
}

2. Unreleased UObjects Holding Memory Indefinitely

Unreal Engine’s `UObject` system requires proper reference handling to avoid memory retention.

Problematic Code

UStaticMeshComponent* MeshComponent = NewObject();

Solution: Use `TWeakObjectPtr` or Explicitly Nullify References

TWeakObjectPtr MeshComponent = CreateDefaultSubobject(TEXT("Mesh"));

3. Blueprint Objects Persisting in Memory Due to Hard References

Blueprint objects with strong references prevent GC from reclaiming memory.

Solution: Use `TSoftObjectPtr` Instead of `TObjectPtr`

TSoftObjectPtr MyBlueprintAsset;

4. High GC Execution Time Due to Large Object Pools

Too many objects in memory increase GC cycle time, causing frame drops.

Solution: Optimize `gc.MaxObjectsNotConsideredByGC`

gc.MaxObjectsNotConsideredByGC=200000

5. Unoptimized Level Streaming Causing GC Overhead

Loading and unloading levels improperly causes GC spikes.

Solution: Use `FlushLevelStreaming()` to Manage Level Memory

UGameplayStatics::FlushLevelStreaming(GetWorld());

Debugging Garbage Collection Performance Issues

1. Monitoring GC Performance in Unreal Engine

stat memgc

2. Checking Memory Usage of Active Objects

stat obj

3. Identifying Objects Preventing GC

obj list class=UStaticMeshComponent

4. Profiling Garbage Collection Impact

stat dumphitches

5. Dumping Unreal Engine’s Object List

obj list

Preventative Measures

1. Use Object Pooling Instead of Frequent Spawning

UObjectPoolComponent* MyPool = NewObject();

2. Set `GC.Interval` to Control GC Execution Frequency

gc.TimeBetweenPurgingPendingKillObjects=30

3. Use Weak References for Non-Essential Objects

TWeakObjectPtr WeakReference = SomeObject;

4. Avoid Unnecessary Hard References in Blueprints

TSoftObjectPtr SoftReference;

5. Manually Trigger Garbage Collection When Needed

GEngine->ForceGarbageCollection();

Conclusion

Garbage collection inefficiencies in Unreal Engine can cause performance degradation, frame stuttering, and memory leaks. By properly managing object lifecycles, using weak references, optimizing GC settings, and debugging performance issues using built-in profiling tools, developers can maintain optimal performance in their games. Proactive memory management is crucial for preventing unexpected performance bottlenecks.

Frequently Asked Questions

1. How do I monitor garbage collection performance in Unreal Engine?

Use `stat memgc`, `stat obj`, and `stat dumphitches` to analyze memory usage and GC impact.

2. Why is my Unreal Engine game stuttering?

GC spikes, excessive actor spawning, and unoptimized object management can cause frame drops.

3. How can I prevent GC from causing performance issues?

Optimize memory usage with object pooling, reduce hard references, and manually trigger GC when needed.

4. Should I manually trigger garbage collection in Unreal Engine?

Only when necessary, such as before loading a new level or after freeing a large number of objects.

5. What is the best way to optimize garbage collection in large open-world games?

Use level streaming efficiently, limit object count per level, and tweak GC settings for high-performance environments.