[jira] [Created] (FLINK-6552) Ambiguous error message when retrieving multiple side-outputs

["Chesnay Schepler (JIRA)" <ji...@apache.org>]

Chesnay Schepler created FLINK-6552:
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             Summary: Ambiguous error message when retrieving multiple side-outputs
                 Key: FLINK-6552
                 URL: https://issues.apache.org/jira/browse/FLINK-6552
             Project: Flink
          Issue Type: Improvement
          Components: Streaming
    Affects Versions: 1.3.0, 1.4.0
            Reporter: Chesnay Schepler


When calling {SingleOutputStreamOperator#getSideOutput(OutputTag<X>} multiple times with the output tags having different types you get the following exception:

{code}
 "Trying to add a side input for the same id with a different type. This is not allowed." 
{code}

This error message is ambiguous, as it could either mean that you cannot add 2 side outputs with the same name but different types or that 2 side outputs with different types cannot be retrieved from a single operator.

Furthermore, the error message contains the concept of node id's (i guess?) which users aren't exposed to. This is confusing and should be reworded to work with operators.

Lastly, i find this limitation rather odd. It is possible for an operator to have multiple side outputs. It is also possible to have a side output with a different type than the main output. Yet, it is not possible to have multiple side outputs with different types.



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