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https://issues.apache.org/jira/browse/BEAM-10166?focusedWorklogId=455080&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-455080
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ASF GitHub Bot logged work on BEAM-10166:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 06/Jul/20 20:46
            Start Date: 06/Jul/20 20:46
    Worklog Time Spent: 10m 
      Work Description: lostluck commented on pull request #12170:
URL: https://github.com/apache/beam/pull/12170#issuecomment-654456518


   This is a good first step! Next up is adding it for use in user error 
returns in exec/pardo.go and similar.
   
   If you did that work already, it's probable that the commit wasn't pushed to 
your branch.
   
   Thanks for your patience in my getting to this. I took a long weekend for 
the US (and Canadian) holiday, and avoided all pretense of work.


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Issue Time Tracking
-------------------

    Worklog Id:     (was: 455080)
    Time Spent: 1h 20m  (was: 1h 10m)

> Improve execution time errors
> -----------------------------
>
>                 Key: BEAM-10166
>                 URL: https://issues.apache.org/jira/browse/BEAM-10166
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-go
>            Reporter: Robert Burke
>            Assignee: Aaron Tillekeratne
>            Priority: P3
>              Labels: beginner, n00b, starter
>          Time Spent: 1h 20m
>  Remaining Estimate: 0h
>
> The Go SDK uses errors returned by DoFns to signal failures to process 
> bundles, and terminate bundle processing. However, if the preceding DoFn uses 
> emitters, rather than error returns, the code has no choice to panic to avoid 
> user code handling or ignoring the cross DoFn error (which could cause 
> dataloss or other correctness problems). 
> All bundle executions are wrapped in 
> `[callNoPanic|https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/core/runtime/exec/util.go#L37]`
>  to prevent worker termination on such panics, and orderly terminate just the 
> affected bundle instead.`callNoPanic` uses Go's built in recover mechanism to 
> get the error and provide a stack trace.
> We can do better.
> The value returned by recover is just an interface{} which means we could 
> detect the specific type of error it is. In particular, we could have the 
> exec package have an error that we can detect. If the recovered value is that 
> error, then we could use that to provide a clearer error message  than a 
> panic stack trace.
> Such an error wrapper would contain: the error in question, the user DoFn 
> that caused it, the debug id of the DoFn node (To be able to relate it back 
> to the plan.)
> See https://gobyexample.com/errors and [other articles on creating custom 
> errors in 
> Go|https://www.digitalocean.com/community/tutorials/creating-custom-errors-in-go].
>  It doesn't need to be complicated.
> Then in `callNoPanic` we could detect this error wrapper and produce a 
> clearer error message based on the existing plan. If not, we can maintain the 
> current behavior. This latter part is necessary to handle panics originating 
> in user code. 
> To avoid mistaken user use which would breach this protocol, we're best off 
> keeping the wrapper unexported from the exec package.



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