presto-main/src/main/java/io/prestosql/sql/planner/optimizations/joins/JoinGraph.java/JoinGraph/toString
class JoinGraph:    @Override
    public String toString()
    {
        StringBuilder builder = new StringBuilder();

        for (PlanNode nodeFrom : nodes) {
            builder.append(nodeFrom.getId())
                    .append(" = ")
                    .append(nodeFrom.toString())
                    .append("\n");
        }
        for (PlanNode nodeFrom : nodes) {
            builder.append(nodeFrom.getId())
                    .append(":");
            for (Edge nodeTo : edges.get(nodeFrom.getId())) {
                builder.append(" ").append(nodeTo.getTargetNode().getId());
            }
            builder.append("\n");
        }

        return builder.toString();
    }