Ingrid Solberg

Performance & Scaling Bug Report

Our in-process cache made p99 latency worse: an optimization we had to roll back

Ingrid Solberg · Nov 4, 2026 · 7 min read

We added a large in-memory cache to a Java service to save Redis round trips. Average latency improved and p99 doubled. The cache pushed the heap into long GC pauses. How we found it in GC logs, why our benchmark missed it, and the measurement method we use now.

Performance & Scaling Bug Report

Our load test said latency stayed flat. The load generator was the bottleneck

Ingrid Solberg · Nov 1, 2026 · 7 min read

A pre-sale load test reported steady 80 ms latency all the way to the target rate. On sale day the API fell over at half that traffic. The test used a closed model with too few virtual users, so it slowed itself down instead of measuring the system. Open models, arrival-rate executors and generator checks.