Function fold_transactions 

pub fn fold_transactions<D>(root: CommitLogDir, de: D) -> Result<(), D::Error>
where
    D: Decoder,
    D::Error: From<Traversal> + From<Error>,

Traverse the commitlog located at the root directory from the start and “fold” its transactions into the provided Decoder.

Starts the traversal without the upfront I/O imposed by Commitlog::open. See Commitlog::fold_transactions for more information.