edf0f754f6
Reader's guide to this PR: The aim is to have a more structured and maintainable approach to generating bytecode from the query AST so that different parts of the query processing pipeline have clearer responsibilities, so that developing new functionality is easier. E.g.: - If you want to implement join reordering -> you do it in `Optimizer` - If you want to implement `GROUP BY` -> you change `QueryPlanNode::Aggregate` to include it, parse it in `Planner` and handle the code generation for it in `Emitter` The pipeline is: `SQL text -> Parser -> Planner -> Optimizer -> Emitter` and this pipeline generates: `SQL text -> AST -> Logical Plan -> Optimized Logical Plan -> SQLite Bytecode` --- Module structure: `plan.rs`: defines the `Operator` enum. An `Operator` is a tree of other `Operators`, e.g. an `Operator::Join` has `left` and `right` children, etc. `planner.rs`: Parses an `ast::Select` into a `Plan` which is mainly a wrapper for a root `Operator` `optimizer.rs`: Makes a new `Plan` from an input `Plan` - does predicate pushdown, constant elimination and turns `Scan` nodes into `SeekRowId` nodes where applicable `emitter.rs`: Generates bytecode instructions from an input `Plan`. --- Adds feature `EXPLAIN QUERY PLAN <stmt>` which shows the logical query plan instead of the bytecode plan --- Other changes: - Almost everything from `select.rs` removed; things like `translate_aggregation()` moved to `expr.rs` - `where_clause.rs` removed, some things from it like `translate_condition_expr()` moved to `expr.rs` - i.e.: there is nothing _new_ in `expr.rs`, stuff just moved there --- Concerns: - Perf impact: there's a lot more indirection than before (`Operator`s are very "traditional" trees where they refer to other operators via Boxes etc) Closes #281
Limbo
Limbo is a work-in-progress, in-process OLTP database management system, compatible with SQLite.
Features
- In-process OLTP database engine library
- Asynchronous I/O support with
io_uring - SQLite compatibility (status)
- SQL dialect support
- File format support
- SQLite C API
- JavaScript/WebAssembly bindings (wip)
Getting Started
Installing:
curl --proto '=https' --tlsv1.2 -LsSf \
https://github.com/penberg/limbo/releases/latest/download/limbo-installer.sh | sh
Limbo is currently work-in-progress so it's recommended that you either use the sqlite3 program to create a test database:
$ sqlite3 database.db
SQLite version 3.42.0 2023-05-16 12:36:15
Enter ".help" for usage hints.
sqlite> CREATE TABLE users (id INT PRIMARY KEY, username TEXT);
sqlite> INSERT INTO users VALUES (1, 'alice');
sqlite> INSERT INTO users VALUES (2, 'bob');
or use the testing script to generate one for you:
pipenv run ./testing/gen-database.py
You can then start the Limbo shell with:
$ limbo database.db
Welcome to Limbo SQL shell!
> SELECT * FROM users LIMIT 1;
|1|Cody|Miller|mhurst@example.org|525.595.7319x21268|33667 Shaw Extension Suite 104|West Robert|VA|45161|`
Developing
Run tests:
cargo test
Test coverage report:
cargo tarpaulin -o html
Run benchmarks:
cargo bench
Run benchmarks and generate flamegraphs:
echo -1 | sudo tee /proc/sys/kernel/perf_event_paranoid
cargo bench --bench benchmark -- --profile-time=5
FAQ
How is Limbo different from libSQL?
Limbo is a research project to build a SQLite compatible in-process database in Rust with native async support. The libSQL project, on the other hand, is an open source, open contribution fork of SQLite, with focus on production features such as replication, backups, encryption, and so on. There is no hard dependency between the two projects. Of course, if Limbo becomes widely successful, we might consider merging with libSQL, but that is something that will be decided in the future.
Publications
- Pekka Enberg, Sasu Tarkoma, Jon Crowcroft Ashwin Rao (2024). Serverless Runtime / Database Co-Design With Asynchronous I/O. In EdgeSys ‘24. [PDF]
- Pekka Enberg, Sasu Tarkoma, and Ashwin Rao (2023). Towards Database and Serverless Runtime Co-Design. In CoNEXT-SW ’23. [PDF] [Slides]
Contributing
We'd love to have you contribute to Limbo! Check out the contribution guide to get started.
License
This project is licensed under the MIT license.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Limbo by you, shall be licensed as MIT, without any additional terms or conditions.