Mock system design interview at Databricks

A live 45-minute round on a question reported in Databricks interviews, run by an AI interviewer that asks one thing at a time, probes what you say, looks at your whiteboard, and weighs what that round is reported to weigh. It ends with a debrief: a score, what was strong, what was missing.

your question

Design a Distributed Key-Value Store

A Dynamo-style store that keeps 10 billion keys on dozens of machines, survives node and rack failures, and lets each caller trade consistency for latency with N, R and W.

You will not see the requirements, the numbers or the design before you start. That is the point.

Walk through it first

What the Databricks round is reported to look like

About an hour, and some loops add a second, lower-level design round with concurrency and running code. Reported prompts include a key-value store that survives a crash, a payment system and a web crawler, and on data-platform teams the round can move into query engines, streaming or storage.

What it weighs

Concurrency: threads, locks and ordering, often down to implementation detail
Durability and recovery: what survives a crash, and how the system comes back
Bottlenecks named and reasoned about, such as disk writes, network calls and threads
Depth: follow-ups continue until they reach the edge of what you know

The common mistake

Stopping at the high-level diagram. Candidates report interviewers spending much of the round on how concurrent transactions or writes are handled and how the system recovers after a failure, so be ready to go below the boxes to threads, locks and recovery.

From public interview guides and candidate reports, and Databricks’s own interview guidance where it publishes any. Not endorsed by Databricks. The interviewer is an AI running in that style; it is practice, not a prediction.

Start the round

Timed · 45 minutesInterview conditions. The AI interviewer owns the clock; the AI Mentor is off.With the AI Mentor · untimedNo clock, and an AI Mentor beside you to ask when you are stuck.

The interviewer’s opening question is free. Answering it is part of Pro. See an example round and its debrief →

The 9 questions this round draws from

Each is reported in Databricks interviews. Pick one to sit, or read its reference design and walk through a strong answer first.

Design a Distributed Key-Value StoreA Dynamo-style store that keeps 10 billion keys on dozens of machines, survives node and rack failures, and lets each caller trade consistency for latency with N, R and W.
drawn
Design Apache AirflowSchedule and run twenty thousand data pipelines as dependency graphs, each run tied to a slice of time, so a failed night can be retried or a year backfilled safely.
Design a Large File Distribution SystemGet a 200 GB checkpoint from one origin onto 10,000 machines in five data centres within minutes, under capped links, verifying every byte.
Design a Distributed Lock ServiceA Chubby-style lock service for 50 k processes: leases, leader election, fencing tokens and watched config, never letting two holders act at once.
Design an Object Storage ServiceAn S3-like store for objects from bytes to terabytes, with eleven nines of durability and strong read-after-write consistency at exabyte scale.
Design a RAG SystemAn assistant that answers employees’ questions from their company’s documents, with citations, only from what each user may open, minutes after edits.
Design GitHub CopilotInline AI code suggestions for 10 M developers, shown within 300 ms of a pause in typing, when most requests are never used.
Design a Vector DatabaseA managed vector database: 10,000 tenants, 20 B vectors, filtered top-k in under 50 ms at 0.95 recall, and writes searchable in seconds.
Design a Container OrchestratorPlace 300,000 containers on 10,000 machines from declared desired state, keep them running through failures, and give every service a stable address.

Other companies: Anthropic · Google · Meta · Amazon · OpenAI · Microsoft · Uber · DoorDash