etch

A fast, embedded database for Rust. 7 dependencies. No C code. No build scripts.

Your Rust structs live in memory, reads are direct field access through an RwLock, and a WAL keeps everything crash-safe on disk. No query engine, no serialization on read — just your types, persisted and durable.

What it is

• Schema is a Rust struct — derive two traits and you're done
• Reads are direct struct access behind an RwLock — no deserialization, no disk I/O
• Writes are atomic and crash-safe via WAL with xxh3 integrity checksums
• 1.7M durable writes/s, 79M reads/s (per record)
• 7 dependencies, pure Rust, compiles in seconds
• Rust-only — your data is your types, with zero-overhead typed access

What it is not

• Not a SQL database — no query language, no query engine, no joins
• Data must fit in memory — your entire state lives in a struct
• Single-process — no replication, no networking, no multi-process access
• No schema migrations — you version your types however you like

Installation

cargo add etchdb

Or add to your Cargo.toml:

[dependencies]
etchdb = "0.3"

Quick start

Define your schema as a struct and derive Replayable + Transactable:

use etchdb::{Replayable, Store, Transactable, WalBackend};
use serde::{Serialize, Deserialize};
use std::collections::BTreeMap;

#[derive(Debug, Clone, Default, Serialize, Deserialize, Replayable, Transactable)]
struct Music {
    #[etch(collection = 0)]
    artists: BTreeMap<String, Artist>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
struct Artist { name: String, genre: String }

That's it — the derive macros handle the rest.

// Open a file-backed store (or Store::<Music>::memory() for tests)
let store = Store::<Music, WalBackend<Music>>::open_wal("data/".into()).unwrap();

// Write — tx.artists is a Collection with typed get/put/delete
store.write(|tx| {
    tx.artists.put("radiohead".into(), Artist { name: "Radiohead".into(), genre: "alt rock".into() });
    tx.artists.put("coltrane".into(), Artist { name: "John Coltrane".into(), genre: "jazz".into() });
    Ok(())
}).unwrap();

// Read — direct struct access, no deserialization
let state = store.read();
assert_eq!(state.artists["coltrane"].name, "John Coltrane");

See the full examples:

cargo run --example hello_derive
cargo run --example hello
cargo run --example contacts

Features

• Derive macros — #[derive(Replayable, Transactable)] eliminates ~60 lines of boilerplate per state type
• Async support — AsyncStore::open_wal + async write/flush for tokio runtimes via block_in_place
• Snapshot compaction — WAL auto-compacts after a configurable threshold, with optional zstd compression (compression feature)
• Two flush modes — immediate fsync or grouped batching for throughput
• Zero-clone writes — Overlay + Transactable captures changes without cloning state
• BTreeMap and HashMap — generic key types (String, Vec<u8>, integers) via EtchKey trait
• Pluggable backends — WalBackend, NullBackend, or bring your own
• Corruption recovery — truncates incomplete WAL entries, keeps valid prefix

Performance

Apple M4 Pro, --release. Run yourself: cargo bench

Each operation is one record — a single struct read or written.

License

MIT