Design a key-value store

Q: Design a key-value store

This question evaluates knowledge of distributed storage and system design concepts, including data modeling, partitioning and consistent hashing, replication and consensus, write/read path trade-offs (e.g., LSM-tree vs B-Tree), compaction, caching, failure handling, and support for efficient range scans in a scalable key–value store.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at Google.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Google during technical interviews.

Question

System Design: Scalable Key–Value Store with Range Scans

You are asked to design a distributed key–value (KV) store that supports the following operations at scale:

get(key)
put(key, value)
delete(key)
range_scan(start_key, end_key, limit)

Assume billions of keys, multi-terabyte datasets, horizontal scalability, and high availability across multiple availability zones. Low p99 latency is desired for point lookups and sequential range scans.

Discuss and justify design choices for the following topics:

Data model and API semantics (keys, values, ordering, TTLs, versioning, deletes/tombstones, range scans)
Partitioning scheme and consistent hashing (how to scale out, balance load, and support efficient range scans; splitting/merging; hot-spot mitigation)
Replication (topology, placement, quorum vs consensus, replica count, cross-AZ)
Write path: LSM-tree versus B-Tree (trade-offs and your choice)
Compaction strategy (policies, amplification, tombstones, TTL expiry, backpressure)
Read path and caching (Bloom filters, block/row cache, readahead/prefetch for scans)
Consistency levels (point reads/writes and range scans; options and guarantees)
Failure handling (node/zone/network failures, recovery, rebalancing, data integrity)

Provide a high-level architecture and call out key trade-offs, pitfalls, and how you will validate the design under load.

Design a key-value store

Quick Overview

Design a key-value store

System Design: Scalable Key–Value Store with Range Scans

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