Potential issue with DUP_SORT

[eranrund]

Hey!

I might be missing something here, but from what it looks like, DUP_SORT is not behaving as expected.

I have the following test code:

use lmdb::{Cursor, Database, DatabaseFlags, Environment, RwTransaction, Transaction, WriteFlags};
use std::sync::Arc;
use tempdir::TempDir;

fn main() {
    let db_tmp = TempDir::new("test").unwrap().into_path();
    let db_path = db_tmp.to_str().unwrap();

    let env = Arc::new(
        Environment::new()
            .set_max_dbs(10)
            .set_map_size(10000000)
            .open(db_path.as_ref())
            .unwrap(),
    );

    let db = env
        .create_db(Some("db_name"), DatabaseFlags::DUP_SORT)
        .unwrap();

    let key = vec![3u8; 32];
    let val = vec![4u8; 32];

    {
        let mut db_txn = env.begin_rw_txn().unwrap();

        db_txn.put(db, &key, &val, WriteFlags::empty()).unwrap();

        db_txn.commit().unwrap();
    }

    {
        let mut db_txn = env.begin_rw_txn().unwrap();

        db_txn.del(db, &key, Some(&val)).unwrap();

        db_txn.commit().unwrap();
    }
}

The code panics at db_txn.del(db, &key, Some(&val)).unwrap(); with Err value: NotFound'`. Is this expected to work?

Thank you!