5 Backend Code Review Mistakes – Small in Detail, Huge in Impact

Five silent bugs that survive staging, only to explode in production.

While there are lots of things to check during a code review, this list has some of the trickiest things that are mostly missed. One tricky thing about items on this list is that they’re usually not caught in staging. Finally, I’ve seen (or heard about) really bad production outages happening because of them. Let’s use these colored symbols to highlight the item’s severity:

🔴 This has caused a production outage that I’ve experienced or heard about.

🟠 This issue slipped through code review and was merged, but was caught before triggering a full outage or caused only limited impact.

1- Thread Safety — Is this class thread safe? 🔴

What is the difference between these 2 classes?

class RequestProcessor {
    private RequestContext context;
}

@Singleton
class RequestProcessor {
    private RequestContext context;
}

The first class assumes a new class is created with every new request, while the second assumes the same class is used for all requests, which can actually cause a disaster.