RecService: Distributed Real-Time Graph Processing at Twitter.

We present RecService, a distributed real-time graph processing engine that drives billions of recommendations on Twitter. Real-time recommendations are framed in terms of a user's social context and real-time events incident on that social context, generated from ad hoc point queries and long-lived standing queries. Results form the basis of downstream processes that power a variety of recommendation products. A noteworthy aspect of the system's design is a partitioning scheme whereby manipulations of graph adjacency lists are local to a cluster node. This eliminates cross-node network traffic in query execution, enabling horizontal scalability and avoiding "hot spots" caused by vertices with large degrees.