Here's a 424-line strict-serializable, distributed, transactional key-value store, including a lazy, immutable hash-tree stored in an eventually-consistent datastore (e.g. Cassandra) and a single root pointer stored in a linearizable kv store (e.g. etcd). Exercised by Maelstrom/Jepsen, checked by Elle for transactional anomalies. Performance plots, concurrency traces, and Lamport diagrams help you understand system behavior.

This is still very much a work in progress--I have several weeks of writing docs and rehearsing ahead of me--but it's coming together as a pretty fantastic testbed for learning algorithms. You can actually see and get reasonable feedback on whether you're doing it right, and understand how different concurrency structures, choices of tuning parameters, etc affect message flow, performance, and correctness.

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