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https://issues.apache.org/jira/browse/GIRAPH-259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426726#comment-13426726
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Jan van der Lugt commented on GIRAPH-259:
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I'm sorry, but I don't agree to the points made by Alessandro. MasterCompute
_should_ be executed before all other vertices are. I don't know if this breaks
the BSP model, since it simply creates another barrier. This will, however, not
result in a scalability issue, since there will always be at most one
MasterCompute. By having the MasterCompute execute before other vertices, it
enables a more intuitive implementation of algorithms like betweenness
centrality, which have different phases. The MasterCompute sets the current
phase in a variable and all the vertices use this variable to determine what
they will do. The only way for MasterCompute to communicate with other vertices
should be aggregators: sending messages to every node would be very costly.
Stanford GPS also uses this model (interleaving vertex and master computation),
but doesn't rely on aggregators, but instead on a global objects map. They are
functionally the same. If MasterCompute would run together with the vertices,
there would be supersteps where the vertices would be idle, because they are
waiting for a value from MasterCompute, which would be very wasteful.
Since MasterCompute depends so heavily on aggregators, given they are its sole
means of communication, I don't think collecting aggregators and running
MasterCompute are completely orthogonal components.
Hope I made this clear enough, otherwise let me know.
> TestBspBasic.testBspPageRank is broken
> --------------------------------------
>
> Key: GIRAPH-259
> URL: https://issues.apache.org/jira/browse/GIRAPH-259
> Project: Giraph
> Issue Type: Bug
> Reporter: Maja Kabiljo
> Assignee: Maja Kabiljo
> Attachments: GIRAPH-259-1.patch, GIRAPH-259-2.patch,
> GIRAPH-259-3.patch
>
>
> Test crashes on line 152 in class SimplePageRankVertex in distributed mode.
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