postings

Postings-list primitives for inverted indices, packaged as a small Rust crate.

Data Model & Invariants

• Doc IDs: u32. Must be dense/contiguous for optimal compression.
• Ordering: Postings lists are always sorted by Doc ID.
• Updates: Segment-based. Deletions are tombstones; updates are delete+add.
• Storage: In-memory by default. Persistence via durability (optional).

Stability & Publishing

This crate is stable for internal use. Public API may change. Use git dependencies for now.

What it is

postings is an in-memory, index-only inverted index meant for candidate generation:

• it does not store document text
• it supports “segment-style” updates
• it provides no-false-negative candidate sets

Usage

Add postings to your Cargo.toml:

[dependencies]
postings = { git = "https://github.com/arclabs561/postings" }

Example (index + candidates):

use postings::{PostingsIndex, PlannerConfig};

let mut idx = PostingsIndex::new();
idx.add_document(0, &["the".to_string(), "quick".to_string(), "fox".to_string()])
    .unwrap();
idx.add_document(1, &["quick".to_string(), "brown".to_string(), "dog".to_string()])
    .unwrap();

// Conjunctive (AND) candidates.
assert_eq!(
    idx.candidates_all_terms(&["quick".to_string(), "dog".to_string()]),
    vec![1]
);

let cfg = PlannerConfig::default();
let plan = idx.plan_candidates(&["quick".to_string()], cfg);
assert!(matches!(plan, postings::CandidatePlan::Candidates(_)));

Features

• postings/serde: enable serde for the in-memory structures.
• postings/persistence: enable save/load helpers via durability + postcard.
• postings/sbits: enable succinct monotone sequences (Elias–Fano) under postings::codec::ef.
• postings/positional: enable positional postings (postings::positional::PosingsIndex).
• postings/roc: enable optional compressed-candidate helpers under postings::positional::roc_candidates.

Optional: positional postings

Enable positional postings behind a feature flag:

[dependencies]
postings = { git = "https://github.com/arclabs561/postings", features = ["positional"] }

Then use postings::positional::PosingsIndex for phrase/proximity evaluation.

Development

cargo test