Versioned & Transactional KV Store for Native & Wasm

AssemblageKV is a very simple embedded key-value store implemented in 100% safe Rust as a log-structured hash table similar to Bitcask. Writes of new or changed values never overwrite old entries, but are simply appended to the end of the storage. Old values are kept at earlier offsets in the storage and remain accessible. An in-memory hash table tracks the storage offsets of all keys and allows efficient reads directly from the relevant portions of the storage. A store can be merged, which discards old versions and builds a more compact representation containing only the latest value of each key.

Features

• simple: log-structured hash architecture, with all keys in memory
• fully versioned: old values remain accessible until merged
• transactional: all reads and writes happen only in isolated transactions
• storage-independent: supports files on native and IndexedDB on wasm

Obligatory Warning

AssemblageKV is a personal project that grew out of my need for a simple KV store that could run on both native and wasm targets. It should go without saying that it is not a battle-tested production-ready database and could at any time eat all of your data. If you need to persist production data, use a real database such as Postgres, SQLite or perhaps look into sled for a KV store in Rust.

Example

let store_name = storage.name().to_string();
let mut store = KvStore::open(storage).await?;
let slot = 0;

{
    let mut current = store.current().await;
    assert_eq!(current.get::<_, u8>(slot, &"key1").await?, None);
    current.insert(slot, &"key1", 1)?;
    current.commit().await?;
}

{
    let mut current = store.current().await;
    assert_eq!(current.get(slot, &"key1").await?, Some(1));
    current.remove(slot, &"key1")?;
    current.commit().await?;
}

{
    let mut current = store.current().await;
    assert_eq!(current.get::<_, u8>(slot, &"key1").await?, None);
    current.insert(slot, &"key1", 3)?;
    current.commit().await?;
}

{
    let current = store.current().await;
    let versions = current.versions(slot, &"key1").await?;
    assert_eq!(versions.len(), 3);
    assert_eq!(current.get_version(slot, &"key1", versions[0]).await?, Some(1));
    assert_eq!(current.get_version::<_, u8>(slot, &"key1", versions[1]).await?, None);
    assert_eq!(current.get_version(slot, &"key1", versions[2]).await?, Some(3));
}

store.merge().await?;
let storage = storage::open(&store_name).await?;
let store = KvStore::open(storage).await?;

{
    let current = store.current().await;
    let versions = current.versions(slot, &"key1").await?;
    assert_eq!(versions.len(), 1);
    assert_eq!(current.get(slot, &"key1").await?, Some(3));
}