Efficient snapshot retrieval over historical graph data

We present a distributed graph database system to manage historical data for large evolving information networks, with the goal to enable temporal and evolutionary queries and analysis. The cornerstone of our system is a novel, user-extensible, highly tunable, and distributed hierarchical index structure called DeltaGraph, that enables compact recording of the historical network information, and that supports efficient retrieval of historical graph snapshots for single-site or parallel processing. Our system exposes a general programmatic API to process and analyze the retrieved snapshots. Along with the original graph data, DeltaGraph can also maintain and index auxiliary information; this functionality can be used to extend the structure to efficiently execute queries like subgraph pattern matching over historical data. We develop analytical models for both the storage space needed and the snapshot retrieval times to aid in choosing the right construction parameters for a specific scenario. We also present an in-memory graph data structure called GraphPool that can maintain hundreds of historical graph instances in main memory in a non-redundant manner. We present a comprehensive experimental evaluation that illustrates the effectiveness of our proposed techniques at managing historical graph information.