Databricks Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at global tech companies like Databricks design, build, and maintain the server-side systems that power large-scale data platforms, APIs, and internal services. Day to day, they write production code, review designs, debug distributed systems, and optimise for reliability, latency, and cost. Freshers typically start by owning small services or components and gradually take on more complex system design work.

Role and Technical Knowledge

1. 1

   Explain how you would design a URL shortener that handles millions of requests per day.

   Cover database choice, key generation, caching, and read/write scaling. Mention trade-offs between consistency and availability.

2. 2

   What happens when you type a URL into a browser and press Enter, from a backend perspective?

   Walk through DNS, TCP, HTTP, load balancers, reverse proxies, application servers, and databases. Show awareness of latency at each step.

3. 3

   How do you ensure data consistency in a distributed system with multiple replicas?

   Discuss replication strategies, quorum reads/writes, eventual consistency, and conflict resolution. Reference real-world examples like Cassandra or DynamoDB.

4. 4

   What is the difference between a process and a thread, and how does it affect backend performance?

   Explain memory sharing, context switching, and concurrency models. Relate it to choosing between multi-threaded and event-driven servers.

Practical Scenarios

1. 5

   You notice a sudden spike in 500 errors from one of your microservices. How do you debug and resolve it?

   Describe checking logs, metrics, and traces, then isolating the service. Mention rollback, scaling, or fixing a recent deployment.

2. 6

   Your database queries are slow under load. What steps do you take to optimise them?

   Talk about indexing, query plans, caching, read replicas, and denormalisation. Emphasise measuring before changing.

3. 7

   How would you handle a situation where a feature you built causes a production outage at 2 AM?

   Show a calm, process-driven approach: mitigate first, communicate, then root-cause. Mention post-mortems and blameless culture.

4. 8

   You need to add a new API endpoint that reads from three different services. How do you ensure it is reliable and fast?

   Discuss timeouts, retries with backoff, circuit breakers, caching, and parallel calls. Mention fallbacks for partial failures.

Coding and Algorithms

1. 9

   Given a large log file, find the top 10 most frequent IP addresses.

   Use a hash map for counting, then a min-heap or quickselect for top K. Discuss memory limits and external sorting if the file is huge.

2. 10

   Implement a rate limiter for an API that allows 100 requests per minute per user.

   Choose between token bucket, leaky bucket, or sliding window. Explain thread safety and distributed coordination using Redis.

3. 11

   Write a function to detect a cycle in a linked list and return the starting node.

   Use Floyd's tortoise and hare algorithm. Explain time O(n) and space O(1), and handle edge cases like empty list.

4. 12

   How would you merge two sorted arrays without using extra space?

   Use two pointers from the end if one array has extra capacity. Discuss time and space complexity and in-place constraints.

Behavioural and HR

1. 13

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

   Use STAR format. Highlight your learning process, resources used, and the outcome. Show curiosity and self-drive.

2. 14

   Describe a situation where you disagreed with a teammate on a technical decision.

   Focus on how you listened, presented data, and reached a consensus. Avoid blaming others and show respect for different views.

3. 15

   Why do you want to work as a backend engineer at a global tech company like Databricks?

   Connect your interest in large-scale systems, data, and cloud to the company's domain. Mention specific products or engineering blogs you follow.

4. 16

   Where do you see yourself in three years, and how does this role fit your goals?

   Show ambition to grow technically and take ownership. Align your goals with the company's need for reliable, scalable backend systems.