The vertex-centric programming model, known as “think like a
vertex”, is being used more and more to support various big graph
processing methods through iterative supersteps that execute in
parallel a user-defined vertex program over each vertex of a graph.
However, the imperative and message-passing style of existing systems
makes defining a vertex program unintuitive. In this paper, we show
that one can benefit more from “Thinking like a vertex” by
“Behaving like a function” rather than “Acting like a procedure”
with full use of side effects and explicit control of message passing,
state, and termination. We propose a functional approach to
vertex-centric graph processing in which the computation at every
vertex is abstracted as a higher-order function and present Fregel, a
new domain-specific language. Fregel has clear functional semantics,
supports declarative description of vertex computation, and can be
automatically translated into Pregel, an emerging imperative-style
distributed graph processing framework, and thereby achieve promising
performance. Experimental results for several typical examples show
the promise of this functional approach.