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From Paolo Castagna <>
Subject Re: Should it be possible to extend BasicVertex<I,V,E,M>?
Date Mon, 21 May 2012 17:08:54 GMT
Benjamin Heitmann wrote:
> On 21 May 2012, at 17:15, Paolo Castagna wrote:
>> A more direct question would be: are Giraph supposed to extend
>> BasicVertex<I,V,E,M> when they do not find a subclass of BasicVertex which
>> their needs?
> No, they are not. However this is not explicitly documented anywhere. 
> Or to say it more clearly: If you look in the javadoc of BasicVertex and if you search
the mailing lists, 
> then you will find that users are discouraged from using/extending BasicVertex, but you
will not find any suggestion of which 
> Vertex to extend instead. I even asked basically the same question once, and got very
indirect answers. 
> But that is okay, I figured it out by trial and error ;) 
> Users are supposed to extend HashMapVertex or EdgeListVertex (both in org.apache.giraph.graph).

Hi Benjamin,
right, I should have seen those (this is a good sign I should stop for today
and continue tomorrow morning). I didn't because I was thinking: "I do not need
my vertexes to be mutable" (since, computing PageRank does not need to change
the topology of a graph), so I was not focusing my attention on the
MutableVertex hierarchy of classes (my mistake).

Now my question would be: why SimplePageRankVertex extends
LongDoubleFloatDoubleVertex? (But, I'll look at this tomorrow).

> If you try to extend them, you will see that you can basically plug-in any kind of existing
class in the <I,V,E,M> signature, 
> as long as the implement the right interfaces, which are all Writable (and WritableComparable
for I). 
> Then you just need to add your compute() method, and you are ready to go. 
> Both HashMapVertex and EdgeListVertex provide implementations of all the housekeeping
that giraph needs.
> Trying to work directly by extending BasicVertex will not work, as a lot of methods are
only accessibly on the same package level. 


> It would probably be a good idea to submit a small javadoc patch which adds documentation
to BasicVertex, that users need to look at those other two classes. 


Thanks again for your help and for pointing me in the right direction.


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