Design driver heat map and discuss consensus

Q: Design driver heat map and discuss consensus

This question evaluates expertise in designing scalable, low-latency real-time systems—covering streaming ingestion via WebSocket, geospatial partitioning into deterministic cells, time-windowed density aggregation and top‑K querying—alongside conceptual knowledge of distributed consensus algorithms (Paxos vs Raft) within the System Design / Distributed Systems domain. It is commonly asked because it probes architectural trade-offs for high-throughput, low-latency geospatial streaming and fault-tolerant replication, combining practical application (component design, data partitioning, real-time aggregation and query serving) with conceptual understanding of consensus protocol differences.

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Question

Real-Time Driver Heat Map with Top-K Busiest Cells, Plus Paxos vs. Raft

Context

You are designing a real-time heat map for a ride-hailing platform. Driver apps continuously send location updates. Rider apps (and internal tools) need to visualize where drivers cluster and fetch the top-K busiest cells within a map region/zoom, with low latency.

Requirements

Real-time ingestion and streaming via WebSocket.
Partition the map into deterministic cell IDs (e.g., S2/Geohash) that align with map zoom levels.
Track driver density per cell over a recent time window (e.g., last 1–5 minutes) and serve the top-K busiest cells for a requested viewport.
Reasonable scale assumptions (tune as needed):
- 1–5 million active drivers globally.
- Each driver sends a location every 2–5 seconds.
- End-to-end latency: P95 <= 1–2 seconds from driver update to client-visible heat change.
High availability across regions; horizontal scalability.

Deliverables

Design the system: ingestion, partitioning, storage, algorithms to maintain and query top-K per region/viewport, and how WebSocket streaming is used.
Explain Paxos and Raft consensus algorithms and highlight key differences.

Design driver heat map and discuss consensus

Real-Time Driver Heat Map with Top-K Busiest Cells, Plus Paxos vs. Raft

Context

Requirements

Deliverables

Solution

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