"oauth2client.transport : Refreshing due to a 401" what exactly this log mean?
<p>I setup a job on google cloud dataflow, and it need more than 7 hours to make it done. My Job ID is 2016-10-10_09_29_48-13166717443134662621. It didn't show any error in pipeline. Just keep logging out "oauth2client.transport : Refreshing due to a 401". Is there any problem of my workers or there is something wrong. If so, how can I solve it?</p>

<p>As a general approach, you should try running the pipeline locally, using the <code>DirectPipelineRunner</code> on a small dataset to debug your custom transformations.</p>

<p>Once that passes, you can use the Google Cloud Dataflow UI to investigate the pipeline state. You can particularly look at <code>Elements Added</code> field in the <code>Step</code> tab to see whether your transformations are producing output.</p>

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<p>In this particular job, there's a step that doesn't seem to be producing output, which normally indicates an issue in the user code.</p>

python google-cloud-dataflow