The basic set/get/delete stuff came together fast, but I underestimated how much the TTL visibility rule would ripple through everything.
Start by clarifying requirements and constraints, then propose a data model using a hash map for O(1) key lookups and a min-heap or time-ordered structure for TTL management. Discuss each operation's implementation, focusing on efficiency and correctness, and cover backup/restore strategies.
Pro tip: Mention that lazy deletion (checking expiration on access) combined with periodic cleanup (e.g., a background thread) balances performance and memory. Also, highlight that scan operations should skip expired entries and consider snapshot isolation for backup.
Ask about expected scale, concurrency needs, persistence requirements, and whether TTL is absolute or sliding. Confirm the exact semantics of each operation.
Propose a hash map for key-value storage, with each entry storing value, optional expiration timestamp, and possibly a version. For TTL management, consider a min-heap or time-ordered structure to efficiently find expired keys.
Detail set, set_with_ttl, get, and delete. For get, check expiration and lazily delete if expired. For set_with_ttl, add to TTL structure. Discuss thread safety if needed.
For scan, iterate over all keys, skipping expired entries. For scan_with_prefix, use a trie or sorted structure for efficient prefix matching, or iterate and filter if simpler.
For backup, serialize the current state (excluding expired entries) to a file or memory buffer. For restore, deserialize and rebuild the data structures, ensuring TTLs are preserved relative to restore time.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.