Test LMDB MDB_DUPSORT write with same key-value.

lmdb_MDB_DUPSORT_write.rs

use lmdb::{Cursor, Transaction};

fn test_lmdb_dup_sort_update_in_place() -> anyhow::Result<()> {
    let db_dir = "lmdb-dir";

    if let Err(err) = std::fs::remove_dir_all(db_dir) {
        if err.kind() != std::io::ErrorKind::NotFound {
            return Err(err.try_into()?);
        }
    }
    std::fs::create_dir_all(db_dir)?;

    let env = {
        let mut builder = lmdb::Environment::new();
        builder.set_map_size(100 * 1024 * 1024);
        builder.open(std::path::Path::new(db_dir)).unwrap()
    };

    let db = env.create_db(
        None,
        lmdb::DatabaseFlags::INTEGER_KEY | lmdb::DatabaseFlags::DUP_SORT,
    )?;


    // Data population #1

    let mut txn = env.begin_rw_txn()?;

    let start_key = 0x2000_1000_3000_0076_u64;
    let key = start_key.to_ne_bytes();

    txn.put(db, &key, &"foobar!", lmdb::WriteFlags::empty())?;

    txn.commit()?;

    let mut txn = env.begin_rw_txn()?;

    let start_key = 0x2000_1000_3000_0076_u64;
    let key = start_key.to_ne_bytes();

    txn.put(db, &key, &"foobar!", lmdb::WriteFlags::empty())?;

    txn.commit()?;

    // Test MDB_SET_RANGE (>=)

    let txn = env.begin_ro_txn()?;

    let mut cursor = txn.open_ro_cursor(db)?;
    let mut count = 0;

    for it in cursor.iter_dup_start() {
        for it2 in it {
            let (a, b) = it2?;
            let key = u64::from_ne_bytes(a.try_into()?);

            let val = std::str::from_utf8(b)?;
            eprintln!("{:#x} {}", key, val);

            count += 1;
        }
    }
    drop(cursor);

    txn.abort();

    eprintln!("count: {}", count);

    let mut txn = env.begin_rw_txn()?;

    let start_key = 0x2000_1000_3000_0076_u64;
    let key = start_key.to_ne_bytes();

    txn.del(db, &key, Some("foobar!".as_ref()))?;

    txn.commit()?;

    let txn = env.begin_ro_txn()?;

    let mut cursor = txn.open_ro_cursor(db)?;
    let mut count = 0;

    for it in cursor.iter_dup_start() {
        for it2 in it {
            let (a, b) = it2?;
            let key = u64::from_ne_bytes(a.try_into()?);

            let val = std::str::from_utf8(b)?;
            eprintln!("{:#x} {}", key, val);

            count += 1;
        }
    }
    drop(cursor);

    txn.abort();

    eprintln!("count: {}", count);

    Ok(())
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    test_lmdb_dup_sort_update_in_place()?;
    eprintln!("Done");
    Ok(())
}

Output

0x2000100030000076 foobar!
count: 1
count: 0
Done