Build a key-value database from scratch. Implement a storage engine with a write-ahead log, indexes and compaction to understand data persistence.
Build it in your language
The tester treats your program as a black box: any language works. These are just the most convenient ones for this project.
Project in preparation: we are completing and verifying the implementation path and its tests. The capabilities below describe the project goal; starting the project is not enabled yet.
“The database saves it” is one of those phrases we take for granted. This challenge takes it apart: you'll see exactly the moment a piece of data stops living only in memory and survives a power cut.
You'll build an LSM-style storage engine: writes to the log, an in-memory memtable, flushes to sorted files, indexes to read quickly, and compaction so the disk doesn't grow forever. And you'll subject it to brutal crashes to confirm it recovers.
14 stages across 4 phases. Every stage comes with its guide and its tests: you move on when they pass.
In-memory API, write-ahead log, and recovery by replaying the log at startup.
Memtable, flushes to immutable sorted files, and merged reads.
Sparse index, Bloom filters and range scans.
Levelled compaction, deletes with tombstones, and measuring the cost.
Build a vector search engine from scratch. Create a vector index with exact search, filters and a simplified HNSW graph for approximate search.
TypeScript · Python · Go
Build a Redis-compatible server from scratch. Implement RESP, an event loop and key expiry, then connect with the official redis-cli.
Go · Rust · Python
Build a SQLite reader from scratch. Open a real database file, walk its B-trees and run SELECT queries by decoding the documented binary format.
Go · Python · Java