Transient Index using B-Trees

transient-btree-index allows you to create a BTree index backed by temporary files. This is helpful if you

• need to index large datasets (thus only working on disk) by inserting entries in unsorted order,
• want to query entries (get and range queries) while the index is still constructed, e.g. to check existence of a previous entry, and
• need support for all serde-serializable key and value types with varying key-size.

Because of its intended use case, it is therefore not possible to

• delete entries once they are inserted (you can use Option values and set them to Option::None, but this will not reclaim any used space),
• persist the index to a file (you can use other crates like sstable to create immutable maps), or
• load an existing index file (you might want to use an immutable map file and this index can act as an "overlay" for all changed entries).

Example

use transient_btree_index::{BtreeConfig, BtreeIndex, Error};

fn main() -> std::result::Result<(), Error> {
    let mut b = BtreeIndex::<u16,u16>::with_capacity(BtreeConfig::default(), 10)?;
    b.insert(1,2)?;
    b.insert(200, 4)?;
    b.insert(20, 3)?;

    assert_eq!(true, b.contains_key(&200)?);
    assert_eq!(false, b.contains_key(&2)?);  

    assert_eq!(3, b.get(&20)?.unwrap());  

    for e in b.range(1..30)? {
        let (k, v) = e?;
        dbg!(k, v);
    }
    Ok(())
}