Databricks·Software Engineer·Technical Phone Screen·Intermediate

IntermediateRejected

Apr 2026

Summary

Databricks SWE interview that went sideways despite solid prep. The candidate knew the material but got caught in a back-and-forth with the interviewer that ate up the clock, and never finished the implementation. Rejected.

Questions Asked (1)

Design a SnapshotSet iterator that supports versioned reads. Walk through your approach, discuss the tradeoffs between design options, and then implement it.

System DesignAlgorithms & Data StructuresTechnical Trade-offs

Author's notes

I'd actually prepped this one, which made the rejection sting more.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements: what operations are needed (create snapshot, iterate, read at version), consistency guarantees, and concurrency expectations. Then discuss design options like copy-on-write, persistent data structures, or versioned logs, highlighting tradeoffs in time/space complexity and concurrency. Finally, implement a chosen design with clean code, explaining key invariants and handling edge cases.

Pro tip: Emphasize that snapshots must be immutable and isolated from concurrent writes; use a persistent data structure (e.g., immutable balanced tree) to achieve O(log n) reads and O(1) snapshot creation, which is often the sweet spot for Databricks-scale workloads.

1. Clarify Requirements

Ask about expected operations (e.g., create snapshot, iterate, read at version), consistency model (snapshot isolation), concurrency (readers vs writers), and performance goals.

2. Explore Design Options

Discuss approaches: copy-on-write (simple but expensive), persistent data structures (efficient snapshots), versioned logs with timestamps (good for append-only), and lock-based vs lock-free concurrency.

3. Analyze Tradeoffs

Compare time/space complexity, snapshot creation cost, read/write performance, memory overhead, and concurrency scalability. Relate to Databricks' needs (e.g., large datasets, concurrent analytics).

4. Implement Chosen Design

Write clean, modular code for the SnapshotSet and iterator, ensuring thread-safety if required. Explain key data structures and invariants.

5. Test and Validate

Walk through edge cases: concurrent writes during iteration, snapshot isolation, empty sets, and version bounds. Suggest unit tests and potential optimizations.

Key Points to Mention

Snapshot isolation and immutability: snapshots must not reflect later writes.
Persistent data structures (e.g., immutable AVL tree, hash array mapped trie) for O(1) snapshot creation and O(log n) reads.
Copy-on-write vs. persistent structures: tradeoff between simplicity and performance.
Concurrency control: lock-free reads via immutable snapshots, or read-write locks for mutable versions.
Versioning: how to assign and retrieve versions (e.g., monotonic counters, timestamps).
Memory management: garbage collection of old versions, reference counting, or time-based retention.

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