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I Optimized the Wrong Thing (A Profiling Story)

· 2 min read
Yisi Liu
Yisi Liu
Game Developer

Six hours. That's how long I spent rewriting Sharpshooters' bullet system before realizing it wasn't the problem.

The Symptom​

During wave 4, the frame rate would stutter every 3–4 seconds. Not a crash, not a freeze — a noticeable 20ms hike that made the game feel janky. I had 40 bullets on screen at peak. My first instinct: bullets are expensive.

What I Did Wrong​

I immediately rewrote the bullet system to use object pooling. Bullets no longer instantiate and destroy — they activate and deactivate from a pool of 100. It took most of a weekend.

The stutter didn't go away.

What I Did Right (Eventually)​

I opened Unity's Profiler. Five minutes after opening it, I found the actual culprit: the damage number UI.

Every hit spawned a TextMeshPro popup that displayed the damage value, animated upward, and then destroyed itself. At peak combat, that was 30–50 Instantiate calls per second — far more garbage than any bullet.

The fix took 45 minutes: a small pool of 20 text popups that get recycled instead of destroyed.

The Irony​

The bullet pooling I spent the weekend on was still a good idea — it'll matter at higher bullet counts. But it was not the source of the problem I was trying to fix.

Rule I'm Taking Forward​

Profile before you optimize. This is advice I'd heard a hundred times. Now I've paid the tuition.

My new process: reproduce the problem, open the Profiler, find the actual spike, then write code. Not before.

What the Profiler Showed​

Frame time: 32ms (frame 1847)
  GC.Collect          12.4ms  ← here
  TextMeshPro.Update   6.1ms
  Physics.Simulate     4.8ms
  Render               5.3ms

The GC.Collect call is the giveaway — that's the garbage collector running because something is allocating heavily. Bullets after pooling: 0 allocations. Text popups before pooling: ~800 bytes per popup × 50 popups/sec = ~40KB/sec of garbage.

Takeaway for Anyone New to Unity Performance​

Three things generate GC pressure more than anything else in my experience:

  1. Instantiate/Destroy — use pooling for anything that spawns frequently
  2. String operations in Update() — $"Score: {score}" creates a new string every frame
  3. LINQ in hot paths — .Where(), .Select() allocate enumerators

Profile first. Know which of the three you're actually hitting before you rewrite anything.

Sharpshooters dev log. Follow along as I build a 3D shooter from scratch.