← Databricks Interview Insights
This question is basically a whole interview by itself.
Start by clarifying requirements: single process vs. multi-process, durability level, and performance constraints. Then propose a layered design: per-file locking for thread safety, atomic write via temp file + rename for crash safety, and a bounded queue for back-pressure. Finally, discuss trade-offs between buffered and direct I/O, and the durability guarantees (e.g., fsync, O_DSYNC) you can realistically offer.
Pro tip: Emphasize that atomic rename is only atomic if the temp file is on the same filesystem, and mention that fsync on the directory is needed to persist the rename. This shows deep OS-level understanding.
Ask about concurrency model (threads/processes), durability needs (e.g., survive power loss), performance targets, and file size. This scopes the solution.
Use per-file locks (e.g., mutex for threads, file locks for processes) to serialize writers. Write to a temp file and atomically rename to the target to avoid partial writes.
Call fsync on the temp file before rename, and fsync the parent directory after rename to ensure the rename is durable. Discuss trade-offs of fsync frequency.
Use a bounded queue per file to limit concurrent writers; when full, block or reject with a clear error. Handle I/O errors by retrying or failing gracefully, and clean up temp files on failure.
Compare buffered vs. direct I/O (performance vs. control), and state realistic durability: with fsync, you get durability after the call returns; without, you risk data loss on crash.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.