Use with rkyv

[dianhenglau]

I'm surprised that fjall can be used with rkyv.

#[derive(rkyv::Archive, rkyv::Deserialize, rkyv::Serialize)]
struct Person {
    id: i64,
    name: String,
    age: i32,
}

fn run_fjall(persons: &[Person]) {
    let keyspace = fjall::Config::new("temp.fjall")
        .open_transactional()
        .unwrap();

    let table_person = keyspace
        .open_partition("table_person", Default::default())
        .unwrap();

    {
        let mut write_tx = keyspace.write_tx();

        for person in persons {
            let bytes = rkyv::to_bytes::<rkyv::rancor::Error>(person).unwrap();
            let key = person.id.to_be_bytes();
            write_tx.insert(&table_person, key, bytes.as_slice());
        }

        write_tx.commit().unwrap();
    }

    println!("fjall:");

    let read_tx = keyspace.read_tx();

    for bytes in read_tx.values(&table_person) {
        let bytes = bytes.unwrap();
        let archived_person = rkyv::access::<ArchivedPerson, rkyv::rancor::Error>(&bytes).unwrap();

        println!(
            "id: {}, name: {}, age: {}",
            archived_person.id, archived_person.name, archived_person.age
        );
    }
}

fn main() {
    let persons = [
        Person {
            id: 1,
            name: "Eleanor".to_string(),
            age: 25,
        },
        Person {
            id: 2,
            name: "Asher Davis".to_string(),
            age: 26,
        },
        Person {
            id: 3,
            name: "Isla Rose Rodriguez".to_string(),
            age: 27,
        },
        Person {
            id: 4,
            name: "Caleb Alexander Jude Nguyen".to_string(),
            age: 28,
        },
    ];

    run_fjall(&persons);
}

I'm surprised because redb cannot be used with rkyv. It will have alignment issue.

Nice! 👍

[marvin-j97]

I wonder if https://github.com/marvin-j97/byteview breaks rykv compatibility, because its inlined representation is possibly aligned to 4 bytes (if the struct starts at 0x0, the first 4 bytes are the len field, followed by 20 bytes of space, so the buffer starts at 0x4).

Maybe the len field needs to be moved to the back of the struct... I'm not sure if there is some way to add a unit test to ensure alignment? Can't move the len field, so I think byteview will need rkyv's unaligned.

[marvin-j97]

I added an rkyv test to byteview: fjall-rs/byteview@084c1d2

I don't think fjall 2.6.0 will play too well with rkyv, it will require the unaligned feature flag.

[dianhenglau]

Got it! Thanks!