Lessons from a Costly Mistake: How I Learned to Prevent Performance Issues in Production

We all make mistakes. Some are small, easily fixed and forgotten. Others have a more significant impact, lingering in our minds long after the issue is resolved. Recently, I made one of those mistakes—a simple code change that snowballed into a big problem in production. This post isn't just about what went wrong but what I learned from the experience. Hopefully, by sharing my story, I can help you avoid making the same mistakes.

The Mistake That Slipped Through

I was confident when I made the change. It seemed harmless at the time—just an inline database query that I thought would improve functionality. It worked fine in the lower environments, so I didn't think twice. But once the code hit production, performance took a serious nosedive. What had seemed like a simple change led to major slowdowns, and users quickly felt the impact.

It wasn't long before my team caught wind of the issue, and I had to face the consequences. This wasn't just a minor hiccup; it was a performance problem that affected the entire application. And worse, it was something that could have been avoided if I'd approached it differently from the start.

Lesson 1: Always Seek a Second Pair of Eyes

One of the biggest lessons I learned is that no matter how confident you feel about a change, if you're dealing with complex code, always ask for someone to review it. I thought I had it under control, but that overconfidence cost me. If I had reached out to a teammate, they might have caught the potential performance issue before it hit production.

Code reviews aren't just a box to tick—they’re a vital part of the development process, especially when your code starts to feel "hacky." I’ve come to realize that if your code feels like a workaround, that’s your cue to ask for help. A fresh perspective can reveal optimization opportunities or highlight potential pitfalls that you might not see.

Lesson 2: Involve the Right People for the Right Code

Not all code reviews are created equal. After this experience, I’ve learned the importance of bringing the right people into the review process. If your change involves database queries, loop in a DBA (Database Administrator) who can help optimize your code. For application logic, don’t just rely on one person’s opinion—get feedback from several developers.

For me, one big takeaway was realizing that I hadn’t involved the right people in my code review process. If I had asked a DBA to look at my query, the performance problem might have been caught earlier. Now, I make sure to invite the right experts into the conversation, especially when dealing with areas that aren't my strongest.

Lesson 3: Testing Isn’t Just About Functionality—It’s About Performance Too

When I wrote that inline query, I tested it in lower environments, and everything seemed fine. The functionality was there, and I assumed that performance would carry over to production. I couldn’t have been more wrong. Lower environments often don’t reflect the real-world conditions that production does, and that’s where my mistake slipped through.

After this incident, I’ve come to appreciate that testing is not just about making sure the code works—it’s about making sure it performs well too. Now, I focus on writing unit tests wherever possible, and when that isn’t an option, I make sure to get thorough code reviews and perform integration testing. Testing in conditions that simulate production as closely as possible is key to avoiding these types of issues.

Lesson 4: Own Your Mistakes and Learn from Them

When the issue was finally caught, my team wasn’t happy, and my boss questioned why I hadn’t been more cautious. It was a hard conversation, and I felt bad for causing the problem. But here's the thing: no one wants to deploy buggy code. What matters most is how you respond when things go wrong.

In that moment, I had to own my mistake, learn from it, and make sure I didn’t repeat it. It wasn’t easy, but it was necessary. I had to keep an open mind and accept that I’d overlooked something important. This experience reminded me that mistakes are part of the learning process. What counts is being able to reflect on them, adjust your approach, and do better next time.

The Path Forward: Practical Steps I’m Taking to Avoid Future Mistakes

So, what am I doing differently now to prevent another performance issue in production? Here are the steps I’ve implemented:

1. Always Ask for Reviews:

   If the code is complex, I no longer hesitate to ask for a second (or third) opinion. It’s not a sign of weakness—it's a smart way to catch potential issues early.

2. Invite the Right Experts:

   I’m now more intentional about who I involve in the code review process. For database queries, I bring in a DBA. For application logic, I seek input from multiple developers to get a well-rounded perspective.

3. Test for Performance, Not Just Functionality:

   I’ve expanded my testing process to focus on performance. Lower environments might not reveal every issue, so I’m making sure to simulate real-world conditions as closely as possible.

4. Reflect and Learn:

   Mistakes are inevitable, but I’m committed to learning from them. Instead of dwelling on what went wrong, I focus on what I can do better next time.

Final Thoughts: Growing from Mistakes

This experience was a humbling reminder that no matter how much experience you have, there's always room to improve. Mistakes happen to all of us, but they don't have to define us. By seeking out code reviews, involving the right people, testing thoroughly, and learning from our mistakes, we can grow as developers and avoid making the same errors in the future.

So, if you find yourself in a similar situation—feeling confident about a change that leads to unexpected issues—don’t be too hard on yourself. Reflect on what went wrong, seek feedback from your team, and take actionable steps to improve your process. With each mistake, we get a little better at what we do.

Until next time, happy computing!

RO out 🎤