During the Google Summer of Code 2019, I worked with Software Heritage: an ambitious research project whose goal is to collect, preserve, and share the whole publicly accessible Free/Open Source Software (FOSS) source code.
The Software Heritage data model is a big Merkle DAG made of nodes like revisions, releases, directories, etc. It is a very big graph, with ~12 B nodes and ~160 B edges, which makes it hard to fit in memory using naive approaches.
Graph compression techniques have been successfully used to compress the Web graph (which is slightly larger than the Software Heritage one) and make it fit in memory. The goal of this GSoC is review existing graph compression techniques and apply the most appropriate one to the Software Heritage case, enabling in-memory processing of its Merkle DAG.