The FlowConnector will sometimes fail when attempting to plan a Flow. If the error message given by PlannerException is vague, use the method PlannerException.writeDOT() to export a representation of the internal pipe assembly. DOT files can be opened by GraphViz and OmniGraffle. These plans are only partial, but you will be able to see where the Cascading planner failed.

Note that you can also create a DOT file from a Flow, by using Flow.writeDOT().

See Debugging Hadoop.