[jira] [Commented] (FLINK-2926) Add a Strongly Connected Components Library Method

["Vasia Kalavri (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-2926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15266205#comment-15266205 ] 

Vasia Kalavri commented on FLINK-2926:
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Hi [~mliesenberg],
thank you for design document. If I understand correctly, the algorithm requires a nested iteration, right?
Inside each round, we need to run 2 pregel steps (forward and backward propagation) and a graph decomposition step. Currently, this is not easy to express in Flink. Our Pregel abstraction does not support multiple phases and does not have a master computation like Giraph does. We will probably need to create a custom delta iteration and handle the different phases with aggregators. Would you like to give it a try and sketch what this delta iteration would look like?

> Add a Strongly Connected Components Library Method
> --------------------------------------------------
>
>                 Key: FLINK-2926
>                 URL: https://issues.apache.org/jira/browse/FLINK-2926
>             Project: Flink
>          Issue Type: Task
>          Components: Gelly
>    Affects Versions: 0.10.0
>            Reporter: Andra Lungu
>            Assignee: Martin Liesenberg
>            Priority: Minor
>              Labels: requires-design-doc
>
> This algorithm operates in four main steps: 
> 1). Form the transposed graph (each vertex sends its id to its out neighbors which form a transposedNeighbors set)
> 2). Trimming: every vertex which has only incoming or outgoing edges sets colorID to its own value and becomes inactive. 
> 3). Forward traversal: 
>                    Start phase: propagate id to out neighbors 
>                    Rest phase: update the colorID with the minimum value seen until convergence
> 4). Backward traversal: 
>                      Start: if the vertex id is equal to its color id propagate the value to transposedNeighbors
>                      Rest: each vertex that receives a message equal to its colorId will propagate its colorId to the transposed graph and becomes inactive. 
> More info in section 3.1 of this paper: http://ilpubs.stanford.edu:8090/1077/3/p535-salihoglu.pdf
> or in section 6 of this paper: http://www.vldb.org/pvldb/vol7/p1821-yan.pdf  



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