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https://issues.apache.org/jira/browse/GIRAPH-243?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13410528#comment-13410528
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Alessandro Presta commented on GIRAPH-243:
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I see your point. I would go with an Edge/EdgeWritable split because it seems
more flexible to different implementations. EdgeListVertex itself becomes much
simpler without the sorting part, efficiency aside (the trick you suggested
would work too in this case, of course).
I made this change in GIRAPH-244.
> EdgeListVertex performance is sub-optimal
> -----------------------------------------
>
> Key: GIRAPH-243
> URL: https://issues.apache.org/jira/browse/GIRAPH-243
> Project: Giraph
> Issue Type: Improvement
> Components: graph
> Reporter: Alessandro Presta
> Assignee: Alessandro Presta
>
> Iterating over outgoing edges (both vertex id and value) in an EdgeListVertex
> is O(n log n): you have to iterate over getOutEdgesIterator and call
> getEdgeValue (which is logarithmic) at each iteration.
> If we store the edge list as a list of Edge<I, E> (instead of the current two
> lists), iteration becomes linear time (which I think is what most people
> expect from an adjacency-list representation).
> Furthermore, I think we can avoid sorting the list by ID: addEdge and
> removeEdge are currently linear-time because we are using an ArrayList, so
> the binary search doesn't help much. If we don't sort, at least addEdge
> becomes amortized constant-time.
> This improvement would require an API change: getOutEdgesIterator should
> iterate over Edge<I, E> as opposed to just I.
> What I propose is to have both iterators (the current one could be called
> getNeighborsIterator), with a default implementation of the neighbors
> iterator in terms of the edges iterator, and optimizations left to
> implementors (e.g. IntIntNullIntVertex).
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