  A1 is an in-memory distributed database used by the Bing search engine to
support complex queries over structured data. The key enablers for A1 are
availability of cheap DRAM and high speed RDMA (Remote Direct Memory Access)
networking in commodity hardware. A1 uses FaRM as its underlying storage layer
and builds the graph abstraction and query engine on top. The combination of
in-memory storage and RDMA access requires rethinking how data is allocated,
organized and queried in a large distributed system. A single A1 cluster can
store tens of billions of vertices and edges and support a throughput of 350+
million of vertex reads per second with end to end query latency in single
digit milliseconds. In this paper we describe the A1 data model, RDMA optimized
data structures and query execution.
