MillenniumDB: A Persistent, Open-Source, Graph Database

TL;DR

MillenniumDB is an open-source, modular graph database engine that supports multiple graph models, combining proven data management techniques with graph-specific algorithms, and outperforms existing engines on real-world data.

Contribution

Introduces MillenniumDB, a novel persistent graph database supporting various models with a modular design and optimized query processing, demonstrated on real-world data.

Findings

Outperforms popular graph database engines on Wikidata queries

Supports multiple graph models with a unified engine

Uses a combination of relational techniques and graph algorithms

Abstract

In this systems paper, we present MillenniumDB: a novel graph database engine that is modular, persistent, and open source. MillenniumDB is based on a graph data model, which we call domain graphs, that provides a simple abstraction upon which a variety of popular graph models can be supported. The engine itself is founded on a combination of tried and tested techniques from relational data management, state-of-the-art algorithms for worst-case-optimal joins, as well as graph-specific algorithms for evaluating path queries. In this paper, we present the main design principles underlying MillenniumDB, describing the abstract graph model and query semantics supported, the concrete data model and query syntax implemented, as well as the storage, indexing, query planning and query evaluation techniques used. We evaluate MillenniumDB over real-world data and queries from the Wikidata knowledge graph, where we find that it outperforms other popular persistent graph database engines (including both enterprise and open source alternatives) that support similar query features.