Ok, I've created an issue:
https://issues.apache.org/jira/browse/GIRAPH-155
Feel free to edit if you think the description is not clear.
By the way, I have also created a vertex reader that reads adjacency
lists but with no values for vertices and edges. That's also a format
that I've seen in several graph data sets. The vertex reader is
essentially a copy of the AdjacencyListVertexReader modified to handle
this format. It's basically an abstract class and subclasses can
override methods to provide default values for vertices and edges
(otherwise values are initialized to null), just like Avery described
below. If you think it's useful I can contribute this.
On Wed, Mar 14, 2012 at 7:39 AM, Avery Ching <ach...@apache.org
<mailto:ach...@apache.org>> wrote:
Thanks for your input. Response inline.
Avery
On 3/13/12 7:14 AM, Dionysios Logothetis wrote:
Hi all,
I'm a new Giraph user, and I'm facing a similar situation. My
input graph is basically in the form of edges defined simply as a
source and destination pair (optionally there could be an edge
value). And these edges might be distributed across multiple
files (this is actually a format I've seen in several graph data
sets).
Without having looked at the internals of Giraph, I originally
imagined that creating a MutableVertex and calling
addVertexRequest for both vertices in an edge and addEdgeRequest
from within the VertexReader would do the trick.
I agree that this idea can work, we also have to have a default
vertex value in case folks add edges to a vertex index only.
Now, this doesn't really work since there needs to be a graph
state created in advance. The graph state is not created until
all vertices have been loaded.
I wouldn't work about graph state here since it's the input
superstep. We can set it for all vertices after creation if need be.
There's also another implication with
potentially multiple workers trying to create the same vertex,
but I think a vertex resolver can handle this, assuming the
resolver is instantiated before the vertices are loaded.
Yup.
Is there a workaround to do this currently apart from
pre-processing the graph?
Not currently. Can you please open a JIRA on
https://issues.apache.org/jira/browse/GIRAPH to put track this
issue? I think we should do it.
Do you think it would be useful to have such functionality?
Yes!
I think it makes sense to handle graph mutations either at the
very beginning or during a execution in a uniform way. By the
way, I'd be interested in contributing to the project.
We'd love to have your contributions, it's a great fit. =)
Looking forward to your response!
Thanks!
On Mon, Mar 12, 2012 at 9:09 PM, Avery Ching <ach...@apache.org
<mailto:ach...@apache.org>> wrote:
Benjamin,
By the way, you're not the first to ask for a feature of this
kind. Perhaps we should consider an alternative format for
loading input vertex data that is based on the edges or data
of the vertices rather than totally vertex-centric. We could
load an edge, or a vertex value and join then all based on
the vertex id. Handling conflicts could be a little
difficult, but perhaps the vertex resolver could handle this
as well.
Avery
On 3/12/12 12:41 PM, Benjamin Heitmann 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.
