Sometimes when I tell people that logging can impact a microservices response time, I get strange looks. 🤨

But I get it. Logging doesn’t feel significant enough to create issues, yet I’ve seen it repeatedly make a considerable difference.

Recently, the team was benchmarking a new microservice that performed well until the request volume passed a few thousand transactions per second.

Once the request volume increased, the p99 latency skyrocketed.

The fix? Two major actions.

1️⃣ Changed a log message in the hot path of every request from Info (logged always) to Debug (only logged when enabled).

2️⃣ Enabling Asynchronous logging puts log messages into a buffer where they can be written to stdout in a different goroutine instead of blocking requests.

These two changes improved the p99 latency by nearly 200%.

This post isn't about not logging.

It's about being intentional:

- Are you logging in the hot path for every request?

- Is the log level correct?

- Do you need every request logged at this point in the process?

Because logging does matter.