Design an in-memory key-value store using maps

Q: Design an in-memory key-value store using maps

This is a System Design interview question from LinkedIn for Software Engineer roles. View the full question and solution on PracHub.

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Question

Design a low-level key-value store library (like an embedded storage engine) under an interview constraint: you may use only map/dictionary-like data structures (plus primitive types / arrays if needed) for your in-memory indexing.

Core API

put(key, value)
get(key) -> value | null
delete(key)

Required properties

Expected O(1) average time for get/put/delete
Safe under concurrent access (multiple threads)
Optional but good to discuss: durability (crash recovery), compaction, TTL/expiration

Deliverable

Explain your design choices (data model, concurrency strategy, persistence approach if any), and how you would test it.

Design an in-memory key-value store using maps

Core API

Required properties

Deliverable

Solution

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