Design a time-series database that ingests millions of metrics per second and answers range queries fast.

Metrics, traces, and IoT data are append-heavy, time-ordered, and rarely updated. A general database handles this badly. The wins come from columnar layout, compression tuned for timestamps, downsampling, and retention. Here is the time-series design interviewers want.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.