DontDestroyOnLoad usage in Unity - Performance & Optimization

Performance: DontDestroyOnLoad usage

MEDIUM IMPACT

This affects how game objects persist across scene loads, impacting memory usage and scene load performance.

Keeping a game manager object alive across multiple scene loads

Unity

void Awake() {
  if (FindObjectsOfType<GameManager>().Length > 1) {
    Destroy(this.gameObject);
    return;
  }
  DontDestroyOnLoad(this.gameObject);
}

Prevents duplicate objects by destroying extras, keeping memory and CPU usage stable.

📈 Performance GainMemory usage remains constant; scene load times stay consistent

Keeping a game manager object alive across multiple scene loads

Unity

void Awake() {
  DontDestroyOnLoad(this.gameObject);
}

// No check for duplicates, so multiple instances accumulate after scene reloads

Multiple instances of the same object accumulate, increasing memory and CPU usage unnecessarily.

📉 Performance CostIncreases memory usage linearly with each scene load; can cause slow scene transitions

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
DontDestroyOnLoad without duplicate check	N/A	N/A	N/A	[X] Bad
DontDestroyOnLoad with duplicate check	N/A	N/A	N/A	[OK] Good

Rendering Pipeline

DontDestroyOnLoad affects the scene management phase by keeping objects alive beyond scene unloads, which means the rendering pipeline must handle these persistent objects each frame.

→Scene Management

→Memory Management

→Rendering

⚠️ BottleneckMemory Management due to accumulating objects if not handled properly

Optimization Tips

1Always check for existing instances before calling DontDestroyOnLoad.

2Destroy duplicate persistent objects to avoid memory leaks.

3Use Unity Profiler to monitor memory and object counts during scene loads.

Performance Quiz - 3 Questions

What is a common performance issue when using DontDestroyOnLoad without safeguards?

A Multiple copies of the same object accumulate, increasing memory use

B The object is destroyed too early causing errors

C The object causes the scene to reload infinitely

D The object disables rendering of other objects

DevTools: Profiler

How to check: Open Unity Profiler, load scenes multiple times, and watch memory usage and object count in Hierarchy.

What to look for: Increasing memory or growing number of persistent objects indicates missing duplicate checks.