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From Avery Ching <ach...@apache.org>
Subject Re: [giraph-users:78] on the type of the VertexID
Date Fri, 09 Sep 2011 17:07:28 GMT
Hi Claudio,

I've added giraph-user@incubator.apache.org since 
giraph-users@googlegroups.com is now deprecated with the move to the 
Apache Incubator.  Thank you for your questions.  I've inlined responses 
below.

Avery

On 9/9/11 3:16 AM, Claudio Martella wrote:
> Hello,
>
>
> I'm setting up my first Giraph application. The idea up to know has 
> been to use a Text as a vertex id (basically my vertices are RDF 
> nodes, therefore i'd like using the URIs as IDs), so I've defined 
> MyVertex as extending Vertex<Text, IntWritable, Text, MyMessage>. In 
> reality I'd like to avoid the IntWritable at all, as I don't really 
> need to keep any state within the vertex, for now, but that's ok.
>
> This is all fine until I write the VertexReader 
> as TextVertexReader<Text, IntWritable, Text> and define the 
> constructor as:
>
> public GraffitiVertexReader(RecordReader<Text, Text> arg) { super(arg); }
>
> Apparently VertexReader requires RecordReader<LongWritable, Text>. Is 
> it mandatory to use a LongWritable?
TextVertexInputFormat uses TextInputFormat (Hadoop provided) 
internally.  And TextInputFormat extends FileInputFormat<LongWritable, 
Text>.  So the RecordReader will have to use the corresponding types.  
LongWritable has the position of the file and the Text is the line of 
text.  If you decide to extend TextVertexInputFormat (good idea), you 
should look at JsonBase64VertexInputFormat as an example.  Your graph 
types need not match the RecordReader<LongWritable, Text> types since it 
will be stored internally of your record reader.

> So the vertex has to be a long? I don't understand the mismatch 
> between the VertexReader constructor and the Vertex definition.
>
Not at all, see above =).  Let me know if it is still unclear.

>
> Thanks!
>
>
> -- 
>     Claudio Martella
> claudio.martella@gmail.com <mailto:claudio.martella@gmail.com>


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