← Google Interview Insights

Google·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Jul 2026

Summary

Google system design round for a software engineer role. The whole session was basically one giant question about building a key-value store, and they expected you to go deep on every layer. Felt like drinking from a firehose.

Questions Asked (1)

Q1

Design a scalable key-value store that supports get, put, delete, and range scan operations.

System DesignTechnical Trade-offsData Modeling
Author's notes

This was the whole interview.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (scale, consistency, latency, data model) and then propose a distributed architecture using consistent hashing for partitioning and replication for fault tolerance. Focus on how range scans are supported efficiently, likely via a sorted storage engine like LSM trees or B-trees, and discuss trade-offs between consistency, availability, and partition tolerance.

Pro tip: Emphasize that range scans require ordered data, so the partitioning strategy must preserve key order (e.g., range partitioning) or use a secondary index; this shows depth beyond basic hashing. Also, proactively discuss how you'd handle hot spots and rebalancing.

1. Clarify Requirements

Ask about scale (data size, QPS), consistency needs (strong vs eventual), latency targets, and whether range scans are frequent or occasional. This shapes the entire design.

2. High-Level Architecture

Propose a distributed system with partitioning (e.g., consistent hashing or range partitioning), replication (e.g., leader-follower or quorum), and a coordinator layer for routing requests. Mention using a sorted storage engine (LSM tree or B-tree) to support range scans.

3. Data Model and Storage Engine

Explain how keys are stored in sorted order to enable efficient range scans. Discuss using SSTables and memtables (LSM) or B-trees, and how tombstones handle deletes.

4. Operations and Consistency

Detail how get, put, delete, and range scan are implemented across partitions. Discuss consistency models (e.g., quorum reads/writes) and how to handle conflicts (e.g., vector clocks or last-write-wins).

5. Scalability and Fault Tolerance

Describe how to scale (adding nodes, rebalancing), handle failures (replication, hinted handoff), and monitor performance. Mention trade-offs like CAP theorem and latency vs consistency.

Key Points to Mention

  • Partitioning strategy: consistent hashing vs range partitioning and impact on range scans
  • Replication and consistency models (e.g., quorum, eventual consistency)
  • Storage engine: LSM trees vs B-trees for write-heavy vs read-heavy workloads
  • Handling deletes with tombstones and garbage collection
  • Range scan implementation: merging results from multiple partitions, using iterators
  • Fault tolerance: replication, failure detection, and recovery mechanisms

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.