Time Series Collections — MongoDB Technical Interview Questions & Answers

Purpose-built collections for time-stamped data.

Time Series Collections

  • Simple meaning: Time series collections store measurements over time (sensor, stock ticks) more efficiently than a normal collection.
  • How to use: db.createCollection("metrics", { timeseries: { timeField: "ts", metaField: "sensorId" } }).
  • Good for IoT. Not for a normal students table.
  • Interview tip: Purpose-built collection. timeField required.

Technical Interview Tip: Time series = measurements + timestamp field.

Code Examples for Time Series Collections

Time Series Collections — working example

db.createCollection("metrics", {
  timeseries: { timeField: "ts", metaField: "deviceId", granularity: "minutes" }
})
db.metrics.insertOne({ ts: ISODate("2026-08-05T10:00:00Z"), deviceId: "sensor-1", temp: 31.2 })
db.metrics.find({ deviceId: "sensor-1", ts: { $gte: ISODate("2026-08-05T00:00:00Z") } })

Time series collections optimize high-ingest timestamped measurements.

How to Explain Time Series Collections to an Interviewer

When a time series collection?

Timestamped measurements, not ordinary business docs