class FDB::DirectoryLayer

def is_prefix_free?(tr, prefix)
  prefix && 
    prefix.length > 0 &&
    !node_containing_key(tr, prefix) && 
    tr.get_range(@node_subspace.pack([prefix]), @node_subspace.pack([FDB.strinc(prefix)]), 
                 { :limit => 1 }).to_a.empty?
end