Tech Freedom Circle

Mar 17, 2026 · Databases

Why HyperLogLog Misses 100M Daily Active Users and How Bitmap Solves It

The article dissects an Alibaba interview question on counting 100 million daily active users, showing why HyperLogLog’s error and lack of per‑user state make it unsuitable, and presents a detailed Bitmap‑based architecture—including sharding, pre‑computation, and ClickHouse integration—to achieve precise, high‑performance analytics.