I started with the in-memory HashMap part and felt fine, then they asked me to define the actual byte format and I kind of froze for a second.
Start by clarifying requirements and assumptions, then propose a simple append-only log design with an in-memory index for fast lookups. Walk through the record format, recovery process, and compaction strategy, emphasizing trade-offs and potential optimizations.
Pro tip: Mention that you would use a checksum per record to detect corruption and ensure durability, and discuss how compaction can be done in the background without blocking reads/writes.
Ask about expected workload (read/write ratio, key/value sizes), durability guarantees, and performance constraints. State assumptions to scope the design.
Define a binary format with fields like key length, value length, key, value, timestamp, and checksum. Explain how it supports put, get, and delete (e.g., tombstones).
Describe an in-memory hash map mapping keys to file offsets for O(1) reads. Explain how put appends to the log and updates the index, and how delete writes a tombstone.
On startup, scan the log sequentially, rebuild the in-memory index, and ignore stale entries (e.g., overwritten keys or tombstones). Mention checksum validation to skip corrupted records.
Propose periodic compaction: write a new log file containing only the latest live records, then atomically swap files. Discuss triggering compaction based on file size or garbage ratio, and handling concurrent access.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.