System designHard

Ride Matching

Pair a rider with a nearby driver in seconds, while everyone keeps moving.

Brief

Functional requirements

System designHard

Pair a rider with a nearby driver in seconds, while everyone keeps moving.

Brief

Let a rider request a trip from a pickup point to a destination

Offer the request to a suitable nearby driver, and to the next one if declined

Show the rider the matched driver's live position until pickup

Track a trip through requested, matched, in progress and completed states

Worked estimates for this brief, not measurements of any real system. Disagree with them out loud — that is the exercise.

Nearby search: each request scans a few cells holding ~50 drivers, so ~50,000 candidate checks/second at peak
Ride requests: ~20 million/day, ~230/second average, ~1,000/second at peak
Location history: 125,000 × 100 bytes × 86,400 s ≈ 1 TB/day if every ping is kept
Location updates: one every 4 seconds, so 125,000 writes/second
Live location state: 500,000 × ~100 bytes ≈ 50 MB — fits in memory many times over
Online drivers at peak: 500,000, as a planning assumption

POST/v1/drivers/me/location
Report position and availability; usually over a socket
POST/v1/trips
Request a trip with pickup and destination
POST/v1/trips/{id}/accept
A driver accepts the offer they were sent
GET/v1/trips/{id}
Trip state and the driver's latest position
POST/v1/trips/{id}/status
Advance the trip: arrived, started, completed

Add components, connect them, and note why each one is there.

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