PlanetScale India Software Engineer Interview: Rounds, Questions and Preparation

What the job involves

Software Engineers at global tech product companies like PlanetScale India design, build, test, and maintain scalable backend services, APIs, and developer-facing tools. Day to day they write production code, review pull requests, debug live issues, and collaborate with product and infrastructure teams to ship reliable features. Freshers typically start on well-scoped components or internal tooling while learning the company's codebase, cloud stack, and engineering practices.

Role and Technical Knowledge

1. 1

   Explain how a relational database handles a write and a read, and where indexes fit in.

   Cover the storage engine path, write-ahead logging or transactions, and how B-tree or hash indexes speed reads. Mention trade-offs like slower writes with more indexes.

2. 2

   What happens when you type a URL into a browser and hit enter?

   Walk through DNS resolution, TCP and TLS handshake, HTTP request, server processing, and rendering. Show you can connect networking layers to real backend services.

3. 3

   How would you design a rate limiter for an API used by many clients?

   Discuss token bucket or sliding window algorithms, where to store counters like Redis, and how to handle distributed consistency. Mention per-user versus per-IP limits.

4. 4

   Compare SQL and NoSQL databases for a high-traffic user profile service.

   Explain schema flexibility, consistency models, scaling patterns, and query needs. Give a reasoned choice rather than declaring one universally better.

Practical Scenarios

1. 5

   A service you own starts returning 500 errors after a deploy. How do you debug it?

   Check dashboards and logs, compare recent changes, reproduce locally if possible, and roll back if impact is high. Show a calm, evidence-based process.

2. 6

   You need to add a new API endpoint that reads from a large table. How do you keep it fast?

   Talk about indexing the right columns, pagination, caching, and query plans. Mention measuring with EXPLAIN before and after.

3. 7

   Your code passes tests locally but fails in CI. What do you check first?

   Look at environment differences, dependency versions, test data, and flaky timing issues. Explain how you would reproduce CI conditions locally.

4. 8

   A teammate's pull request has a bug you spotted. How do you handle it?

   Leave a specific, kind comment with a suggested fix and reasoning. Emphasise that code review is collaborative, not personal.

Behavioural and HR

1. 9

   Tell me about a time you had to learn a new technology quickly for a project.

   Use a concrete project example, describe your learning method, and end with the result. Show curiosity and self-direction.

2. 10

   Describe a situation where you disagreed with a teammate. How did you resolve it?

   Focus on listening, data, and finding common ground. Avoid blaming others and highlight the outcome.

3. 11

   Why do you want to work at a product company like PlanetScale India?

   Connect your interest in databases, developer tools, or scalable systems to the company's domain. Show you understand what the company builds.

4. 12

   Where do you see yourself in three years as a software engineer?

   Talk about deepening technical skills, owning larger components, and mentoring juniors. Keep it realistic and aligned with continuous learning.

Coding and Problem Solving

1. 13

   Given an array of integers, find two numbers that add up to a target sum.

   Explain the brute-force approach first, then optimise with a hash map to O(n). Discuss edge cases like duplicates and no solution.

2. 14

   Reverse a linked list iteratively and recursively.

   Show pointer manipulation carefully and explain time and space complexity. Mention how recursion uses stack space.

3. 15

   Design a function to merge two sorted arrays into one sorted array in place.

   Discuss the two-pointer technique and why merging from the end avoids overwriting. Cover time and space complexity.

4. 16

   How would you detect a cycle in a linked list?

   Describe Floyd's tortoise and hare algorithm and why it works. Mention the alternative of using a hash set and its space cost.