How to check if there is any error in the flow?

[carusyte]

If any error is thrown in the mapper/reducer, how to catch it after the run has finished?

[chrislusf]

From mapper/reducer, any outputs to os.Stderr are all sent back to the driver. But need ideas on how to return it as an error. Often the os.Stderr may just be outputs from println() and not necessarily an error.