[jira] [Created] (FLINK-8041) Recommended Improvements for Gelly's Connected Components Algorithm

["Christos Hadjinikolis (JIRA)" <ji...@apache.org>]

Christos Hadjinikolis created FLINK-8041:
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             Summary: Recommended Improvements for Gelly's Connected Components Algorithm
                 Key: FLINK-8041
                 URL: https://issues.apache.org/jira/browse/FLINK-8041
             Project: Flink
          Issue Type: Improvement
          Components: Gelly
    Affects Versions: 1.3.2
         Environment: Linux, IntelliJ IDEA
            Reporter: Christos Hadjinikolis
            Priority: Minor
             Fix For: 1.4.0


At the moment, the ConnectedComponents algorithm that comes with Flink's native Graph API (Gelly) has two issues:
1. It relies on the user to provide correct values for in the vertices DataSet. Based on how the algorithm works, these values must be of type Long and be unique for every vertex. If the user provides the same values for every vertex (e.g. 1) the algorithm still works but as those values are used for the identification of the different connected components, one will end up with a single connected component and will have no clue as to why this happened. This can be easily fixed in two ways: either by checking that the values that appear alongside vertex-ids are unique and informing the user if not, or by generating those values for every vertex before the algorithm is ran. I have a running implementation of the second way and I really think it is an appropriate solution to this problem.
2. Once the connected components are identified, one has to apply additional transformations and actions to find out which is the biggest or the order of the connected components in terms of their size. Alternatively, the algorithm can be implemented so that numerical ids that are given to each component reflect their ranking when ordered based on size, e.g. connected component 1 will be the biggest, connected component 2 should be the second biggest and so on.  



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