Overview

limousine_engine provides procedural macros to automatically generate an (immutable) hybrid index design:

use limousine_engine::prelude::*;

create_immutable_hybrid_index! {
    name: ExampleHybridIndex,
    layout: {
        0 | 1 => btree(16),
        _ => pgm(4),
    }
}

To generate a design, we provide a name for the structure, and a layout description, which resembles the syntax of a Rust match expression. In this example, the first two layers are BTree layers with a fanout of 16, and the rest of the layers are PGM layers with an epsilon parameter of 4. All of this is parsed and generated into a static implementation at compile time by the procedural macro. We can also generate efficient pure designs using this approach:

use limousine_engine::prelude::*;

create_immutable_hybrid_index! {
    name: BTreeIndex,
    layout: {
        _ => btree(16),
    }
}

create_immutable_hybrid_index! {
    name: PGMIndex,
    layout: {
        _ => pgm(4),
    }
}

We can then use these generated structs to perform queries:

// Load the first two layer of the index from memory
let index = ExampleHybridIndex::<i32, i32>::load("path_to_index", 2)?;

// Range query
for (key, value) in index.range(&0, &100) {
    println!("found entry: {key:?} {value:?}");
}