This module is used by Saito to create and interact with a Google Dense Hashmap. In order for it to work you will need to have already installed the Google Sparsehash library. If you have not done this, you can take care of it as follows:

experimental in-memory key:value cache where keys are binary Buffers

A fast & memory-efficient data structure that cat tell if it saw a string before

A fast, memory efficient hash map for C++; Gregory Popovitch (2016).