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delta-kernel-rs

Delta-kernel-rs is an experimental Delta implementation focused on interoperability with a wide range of query engines. It currently only supports reads.

The Delta Kernel project is a Rust and C library for building Delta connectors that can read (and soon, write to) Delta tables without needing to understand the Delta protocol details. This is the Rust/C equivalent of Java Delta Kernel.

Building

To get started, install Rust via rustup, and just as a command runner - then clone the repository. Before running tests, we need to load reference data from the Delta Acceptance Tests via:

just load-dat

Then we can build and run tests via

cargo test --features acceptance,default-client

or using just again:

just test

Development

delta-kernel-rs is still under heavy development but follows conventions adopted by most Rust projects.

Architecture

See arcitecture.md document (currently wip)

Some design principles which should be considered:

  • async all the things, but ideally no runtime. Basically delta-core should have async traits and implementations, but strive to avoid the need of a runtime so that implementers can use tokio, smol, async-std, or whatever might be needed. Essentially, we want to strive to design without actually evaluating futures and leave that to the implementers on top of possible
  • No DeltaTable. The initial prototype intentionally exposes the concept of immutable versions of tables through the snapshot API. This encourages users to think about the Delta table state more accurately.
  • Consistently opinionated. In #delta-rs we have some object-oriented APIs and some builder APIs. delta-kernel-rs uses builder-style APIs and that we should adopt consistently through delta-core-rs
  • "Simple" set of default-features enabled to provide the basic functionality with the least necessary amount of dependencies possible. Putting more complex optimizations or APIs behind feature flags
  • API conventions to make it clear which operations involve I/O, e.g. fetch or retrieve type verbiage in method signatures.

Tips

  • When developing, rust-analyzer is your friend. rustup component add rust-analyzer
  • When also developing in vscode its sometimes convenient to configure rust-anmalyzer in .vscode/settings.json.
{
  "editor.formatOnSave": true,
  "rust-analyzer.cargo.features": ["default-client", "acceptance"]
}
  • The crate's documentation can be easily reviewed with: cargo docs --open