Crate mmtkvdb

Expand description

Key-value database using LMDB

Caveats / Safety

Because of how memory-mapped I/O is being used and also because of certain assumptions of the underlying LMDB API, opening environments and databases requires unsafe Rust when using this library.

Do not open the same environment twice in the same process (see documentation of EnvBuilder). The file format is platform specific, so endianness and word size must not change across use.

When opening an already existing database, all options must be compatible with the previously used options (see documentation of DbOptions).

Stale readers might need to be cleared manually, see EnvRo::clear_stale_readers.

Example

use mmtkvdb::{self as kv, Txn as _};
use tempfile::tempdir;
fn doit() -> Result<(), std::io::Error> {
    let location = tempdir()?;
    let db1_opts = kv::DbOptions::new().name("db1");
    let db2_opts = kv::DbOptions::new().key_type::<str>().value_type::<i32>().name("db2");
    let env_builder = kv::EnvBuilder::new().dir(location.path()).max_dbs(2);
    {
        let mut env = unsafe { env_builder.open_rw()? };
        let db1 = unsafe { env.create_db(&db1_opts)? };
        let db2 = unsafe { env.create_db(&db2_opts)? };
        let mut txn = env.txn_rw()?;
        txn.put(&db1, "key1".as_bytes(), "value1".as_bytes())?;
        txn.put(&db2, "Prime", &17)?;
        txn.commit()?;
    }
    {
        let env = unsafe { env_builder.open_ro()? };
        let db1 = unsafe { env.open_db(&db1_opts)? };
        let db2 = unsafe { env.open_db(&db2_opts)? };
        let txn = env.txn_ro()?;
        assert_eq!(txn.get(&db1, "key1".as_bytes())?, Some("value1".as_bytes()));
        assert_eq!(txn.get_owned(&db2, "Prime")?, Some(17));
    }
    location.close()?;
    Ok(())
}
doit().expect("error during database access")