Error: Cannot find prevKey when creating shard_id

[redpanda-f]

Hi,
we seem to have a simple setup where we try to populate the DB with some keys and values as follows:

fn main() {
    std::fs::remove_dir_all("qmdb_testdir").unwrap();
    std::fs::create_dir_all("qmdb_testdir").unwrap();
    let config = Config::from_dir("qmdb_testdir");
    AdsCore::init_dir(&config);
    let mut ads = AdsWrap::<SimpleTask>::new(&config);

    let tasks_per_block = 10_000;

    if tasks_per_block >= (1 << IN_BLOCK_IDX_BITS) {
        panic!("tasks_per_block {} is too large", tasks_per_block);
    }

    let mut cset = ChangeSet::new();
    let mut rng = rng();
    let mut known_keys = HashSet::new();
    for i in 0..1_000 {
        let key = {
            loop {
                let key: Vec<u8> = (0..32).map(|_| rng.random()).collect(); // Generate a random 32-byte key
                if !known_keys.contains(&key) {
                    known_keys.insert(key.clone());
                    break key;
                }
            }
        };
        known_keys.insert(key.clone());
        let value: Vec<u8> = (0..32).map(|_| rng.random()).collect(); // Generate a random 32-byte value
        let shard_id = byte0_to_shard_id(key[0]) as u8;
        let mut key_array = [0u8; 32];
        key_array.clone_from_slice(&key[..32]); // Copy the first 32 bytes into the array
        cset.add_op(OP_CREATE, shard_id, &key_array, &key[..], &value[..], None);
    }
    cset.sort();
    let task = SimpleTask::new(vec![cset]);
    let task_list = vec![RwLock::new(Some(task))];
    let height = 1;
    let task_count = task_list.len() as i64;
    println!("task count {}", task_count);
    // task id's high 40 bits is block height and low 24 bits is task index
    let last_task_id = (height << IN_BLOCK_IDX_BITS) | (task_count - 1);
    println!("last task id {}", last_task_id);

    ads.start_block(height, Arc::new(TasksManager::new(task_list, last_task_id)));
    let shared_ads = ads.get_shared();
    shared_ads.add_task((height << IN_BLOCK_IDX_BITS) | (task_count - 1));
    ads.flush();
}

However, we face the following error:

task count 1
last task id 16777216
FF key = [0, 108, 70, 149, 121, 15, 101, 231, 142, 0] file_pos = 360880

thread '<unnamed>' panicked at /home/useruser/.cargo/git/checkouts/qmdb-cd830a515878d17f/8def52e/qmdb/src/updater.rs:288:13:
Cannot find prevKey when creating shard_id=0 key=[0, 108, 198, 199, 203, 97, 109, 156, 191, 210, 198, 95, 229, 45, 47, 196, 143, 176, 226, 10, 122, 103, 17, 158, 83, 242, 218, 0, 169, 2, 21, 64]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
FF key = [209, 152, 131, 169, 164, 169, 42, 223, 38, 0] file_pos = 362176

thread '<unnamed>' panicked at /home/useruser/.cargo/git/checkouts/qmdb-cd830a515878d17f/8def52e/qmdb/src/updater.rs:288:13:
Cannot find prevKey when creating shard_id=13 key=[209, 152, 241, 2, 85, 83, 240, 255, 61, 21, 92, 240, 207, 62, 174, 73, 253, 9, 86, 245, 45, 146, 221, 220, 35, 43, 90, 62, 119, 120, 152, 172]
...

What is going wrong here, especially when this is the first set of additions to DB with all distinct keys.

[absolute0kelvin]

        known_keys.insert(key.clone());
        let value: Vec<u8> = (0..32).map(|_| rng.random()).collect(); // Generate a random 32-byte value
        //let mut key_array = [0u8; 32];
        //key_array.clone_from_slice(&key[..32]); // Copy the first 32 bytes into the array
        let kh = hasher::hash(&key[..]);
        let shard_id = byte0_to_shard_id(kh[0]) as u8;
        cset.add_op(OP_CREATE, shard_id, &kh, &key[..], &value[..], None);

You need to calculate the key hash, instead of key_array

[absolute0kelvin]

    let shared_ads = ads.get_shared();
    for idx in 0..task_count {
        let task_id = (height << IN_BLOCK_IDX_BITS) | idx;
        //pump tasks into QMDB's pipeline
        //in this demo we prepared all the tasks before pumpling them
        //in production you can pump a task immediately after getting it ready
        shared_ads.add_task(task_id);
    }
    ads.flush();

And please use a loop for add_task