PerformanceThe cache was working perfectly. That was the problem.
A 99.2% hit rate hid nine cache stampedes. What singleflight fixed, what it did not, and the two bugs that only exist under concurrency.
Performance
Finding Errors in Log Streams
Rank and select turn two expensive log queries into constant-time lookups. What that costs, what it buys, and why the same code can honestly report both 2ns and 13ns.