[jira] [Commented] (FLINK-4624) Gelly's summarization algorithm cannot deal with null vertex group values

["Martin Junghanns (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-4624?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15502534#comment-15502534 ] 

Martin Junghanns commented on FLINK-4624:
-----------------------------------------

As stated on the mailing list, the problem is that the output of the {{VertexGroupReducer}} represents two types of tuples: one for each vertex, where {{VertexGroupItem.f2 == null}} and one for the whole group where {{VertexGroupItem.f2 == value of type VV}}. A simple fix would be to output the value in all cases, but this increases intermediate data volume and is not necessary for the algorithm to work correctly. However, the output tuples are sent to a filter + map function after the groupreduce, so at least there would be no additional network traffic. I tested it and it fixes the issue.

I also tried to use {{Either<NullValue, VV>}} for {{f2}}. However, I am getting exceptions from the serializer becaue Either.Right and Either.Left are not serializable. Am I understanding the either type wrong? I thought this is the purpose of that type?

> Gelly's summarization algorithm cannot deal with null vertex group values
> -------------------------------------------------------------------------
>
>                 Key: FLINK-4624
>                 URL: https://issues.apache.org/jira/browse/FLINK-4624
>             Project: Flink
>          Issue Type: Bug
>          Components: Gelly
>            Reporter: Till Rohrmann
>            Assignee: Martin Junghanns
>             Fix For: 1.2.0
>
>
> Gelly's {{Summarization}} algorithm cannot handle null values in the `VertexGroupItem.f2`. This behaviour is hidden by using Strings as a vertex value in the {{SummarizationITCase}}, because the {{StringSerializer}} can handle null values. 



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