How big Tensorflow graph can be?

Is there a practical limit on the size of graph Tensorflow can handle? We are looking at large computation problems that could expand to hundreds of million or billions of nodes in the graph, am wondering if Tensorflow can automatically handle the construction and distributed execution of such large graphs over multiple computers using CPUs? Or we have to manually break the graph into smaller ones before sending to Tensorflow?

Any first-hand experience in handling large graphs are great appreciated, such as the maximum graph size you were able to run in Tensorflow, and any potential pitfalls etc,