  We present BigSparse, a fully external graph analytics system that picks up
where semi-external systems like FlashGraph and X-Stream, which only store
vertex data in memory, left off. BigSparse stores both edge and vertex data in
an array of SSDs and avoids random updates to the vertex data, by first logging
the vertex updates and then sorting the log to sequentialize accesses to the
SSDs. This newly introduced sorting overhead is reduced significantly by
interleaving sorting with vertex reduction operations. In our experiments on a
server with 32GB to 64GB of DRAM, BigSparse outperforms other in-memory and
semi-external graph analytics systems for algorithms such as PageRank,
BreadthFirst Search, and Betweenness-Centrality for terabyte-size graphs with
billions of vertices. BigSparse is capable of highspeed analytics of much
larger graphs, on the same machine configuration.
