System designHardsd-g714

Subject Storage engineLevel Senior–Staff~45 minCommon in Storage & CDN interviewsIndustries Technology

Question

Design a time-series storage engine for metrics/observability: ~5 million unique series, ~2 million samples/sec ingested (timestamp + float per series), queries that scan a few series over a time range plus dashboard aggregations, and retention that keeps raw data 15 days but rolled-up data for a year. How do you ingest, store, compress, and query this efficiently while keeping cost down?

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.