ToyDB rewritten: a distributed SQL database in Rust, for education

Summary

toyDB Distributed SQL database in Rust, built from scratch as an educational project. Main features: I originally wrote toyDB in 2020 to learn more about database internals. Since then, I've spent several years building real distributed SQL databases at CockroachDB and Neon. Based on this experience, I've rewritten toyDB as a simple illustration of the architecture and concepts behind distributed SQL databases. toyDB is intended to be simple and understandable, and also functional and correct. Other aspects like performance, scalability, and availability are non-goals -- these are major sources of complexity in production-grade databases, and obscure the basic underlying concepts. Shortcuts have been taken where possible. Documentation Architecture guide: a guided tour of toyDB's code and architecture. SQL examples: walkthrough of toyDB's SQL features. SQL reference: reference documentation for toyDB's SQL dialect. References: research materials used while building toyDB. Usage With a Rust compiler installed, a local five-node cluster can be built and started as: $ ./cluster/run.sh Starting 5 nodes on ports 9601-9605 with data under cluster/*/data/. To connect to node 1, run: cargo run --release --bin toysql toydb4 21:03:55 [INFO] Listening on [::1]:9604 (SQL) and [::1]:9704 (Raft) toydb1 21:03:55 [INFO] Listening on [::1]:9601 (SQL) and [::1]:9701 (Raft) toydb2 21:03:55 [INFO] Listening on [::1]:9602 (SQL) and [::1]:9702 (Raft) toydb3 21:03:55 [INFO] Listening on [::1]:9603 (SQL) and [::1]:9703 (Raft) toydb5 21:03:55 [INFO] Listening on [::1]:9605 (SQL) and [::1]:9705 (Raft) toydb2 21:03:56 [INFO] Starting new election for term 1 [...] toydb2 21:03:56 [INFO] Won election for term 1, becoming leader A command-line client can be built and used with node 1 on localhost:9601 : $ cargo run --release --bin toysql Connected to toyDB node n1. Enter !help for instructions. toydb> CREATE TABLE movies (id INTEGER PRIMARY KEY, title VARCHAR NOT NULL); toydb> INSERT INTO movies...