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From David Garcia <dgar...@potomacfusion.com>
Subject Re: Calling BspUtils.createVertexResolver from a TextVertexReader ?
Date Mon, 12 Mar 2012 20:49:11 GMT
Ah, I see.  So based on what you've written here, I suspect that you will
need to override, at the very least, your record reader.  Every call to
next() will throw away the previous line.  So, if there are two vertices
on that line, I don't think that the canned TextInputFormat will parse
your data correctly.  Writing a vertexRecordReader is not too hard. .
.just make sure you know where the singletons are.  I was bit by
singletons a couple months ago when making a giraph vertexRecordReader.

-David

On 3/12/12 2:41 PM, "Benjamin Heitmann" <benjamin.heitmann@deri.org> wrote:

>
>On 12 Mar 2012, at 18:15, David Garcia wrote:
>
>> Not sure what you're asking about.  getCurrentVertex() should only ever
>> create one vertex.  Presumably it returns this vertex to the calling
>> function. . .which is called in loadVertices() I think.
>
>Thanks David. 
>
>I am asking this question because I have a text input format which is
>very different from a node adjacency list.
>The most important difference, is that each line of the input file
>describes two nodes.
>The other important difference is that a node might be described on more
>then one line of the input.
>
>I have multiple gigabits of input, so it would be very beneficial to
>directly load the input into Giraph.
>Otherwise the overhead of converting the input to some sort of node
>adjacency list is so big,
>that it might be a show-stopper regarding the suitability of Giraph.
>
>
>
>
>
>
>
>For more details, here is the text from my previous email:
>=========================[snip]===========
>
>I am wondering if it would be possible to parse RDF input files from a
>TextInputFormat class.
>
>The most suitable text format for RDF is called "NTriples", and it has
>this very simple format:
>
>subject1 predicate1 object1 .\n
>subject1 predicate2 object2 .\n
>...
>
>So each line contains the subject, which is a vertex, a predicate, which
>is a typed edge, and the object, which is another vertex.
>Then the line is terminated by a dot and a new-line.
>
>In Giraph terms, the result of parsing the first line would be the
>creation of a vertex for subject1 with an edge of type predicate1,
>and then the creation of a second vertex for object1. So two vertices
>need to be created for that one line.
>
>Now the second line contains more information about the vertex subject1.
>So in Giraph terms, the vertex which was created for subject1 needs to be
>retrieved/revisited and an edge of type predicate2,
>which points to the new vertex object2 needs to be created. And vertex
>object2 needs to be created.
>
>Just to point it out, such RDF NTriples files are unsorted, so
>information about the same vertex might appear e.g. at the first and at
>the last line 
>of a multiple GB big file.
>
>Which interface can be used in a TextInputFormat/VertexReader in order to
>find an already created vertex ?
>
>Are there any other issues when VertexReader.getCurrentVertex() creates
>two vertices at the same time ?
>
>
>A second related question:
>If I have multiple formats for my input files, how would I implement that
>? 
>Just by adding a switch to the logic in getCurrentVertex() ? Or is there
>a better way to switch the input logic based on the file type ?
>All my input files would result in the same kind of Vertex being created.
>
>
>My motivation for doing this, in short:
>I have a large amount of RDF NTriples data which is provided by DBPedia.
>It amounts to somewhere between 5 GB and 20 GB,
>depending on which subset is used. Expressing this RDF data, so that each
>vertex is completely described in one text line,
>would require me to load it into an RDF store first, and then reprocess
>the data. In terms of RDF stores, that is already a non-trivial amount of
>data
>requiring quite a bit of hardware and tweaking. That is the reason why it
>would be valuable to directly load the RDF data into Giraph.
>
>
>
>


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