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From Claudio Martella <claudio.marte...@gmail.com>
Subject Re: giraph stability problem
Date Mon, 23 Jan 2012 15:16:42 GMT
There's not much you can do If you're trying an algorithm with
exponential space complexity and you don't have enough disk space.
What do you suggest?

On Mon, Jan 23, 2012 at 4:13 PM, Deepak Nettem <deepaknettem@gmail.com> wrote:
> I have seen people run into this problem when doing Graph Processing
> directly on top of Hadoop too. This kind of an approach would take
> exponential space.
>
> While the proposed solution would prevent the OOM problem, eventually one
> would run out of disk space.
>
>
> On Mon, Jan 23, 2012 at 6:16 AM, Claudio Martella
> <claudio.martella@gmail.com> wrote:
>>
>> Hi,
>>
>> I've been struggling with a similar problem and that's why i've
>> started working on the out-of-core message management, when the memory
>> shrinks. Your particular problem can get to an upper bound of
>> exponential space complexity, which you experience with the OOM. the
>> possible paths you can extract for each source vertex are about
>> O(d^l), where d is the average degree of the graph and l is the max
>> length of the extracted path (if you do shortest paths, then it's the
>> diameter).
>>
>> Giraph is all good and fast but it's all in-memory and for this reason
>> it currently lacks a solution to your problem. I suggest you wait
>> until GIRAPH-45 is ready (I should write an email tonight about that
>> patch).
>>
>> Hope it makes sense to you,
>> Claudio
>>
>> On Mon, Jan 23, 2012 at 10:56 AM, André Kelpe
>> <efeshundertelf@googlemail.com> wrote:
>> > Hi list,
>> >
>> > I have been investigating giraph for a week now and I have a huge
>> > stability
>> > problem. I am running the trunk against a CDH3u2 hadoop cluster. The
>> > problem
>> > I am trying to solve goes as follows:
>> >
>> > In a graph there are 3 kinds of vertices:
>> >
>> > 1: end of the world vertices, which have only 1 connected edge
>> > 2: bivalent vertices, which have exactly 2 connected edges
>> > 3: multivalent vertices that have n-edges connected (n>2)
>> >
>> > The goal is now to calculate for each vertex that is not in category 2
>> > all
>> > the paths to the other reachable non bivalent vertices. One could say
>> > all
>> > pathes between all non-bivalent vertices.
>> >
>> > To give an example:
>> >
>> >                                        [9]
>> >                                         |
>> >                                         |
>> >                                        <12>
>> >                                         |
>> >                                         |
>> >      [5]-----<13>-----[6]-----<11>-----[7]-----<10>-----[8]
>> >
>> > In this path I want to know that [5] forms a path to [7] via the edges
>> > <13>
>> > and <11>. [7] forms a path via <12> with [9], via <10> with
[8] and via
>> > <11><13> with [5]. You get the idea... Directionality is not important.
>> >
>> > The algorithm I have is pretty straight forward, in superstep 0 all
>> > vertices
>> > that are non-bivalent send a message to their neighbours via which edge
>> > they
>> > are reachable. In all following supersteps the bivalent vertices are
>> > simply
>> > forwarding this information and the non-bivalent ones are terminating
>> > the
>> > algorithm. The messages that they sent are made using Textwritable
>> > instances
>> > encoding the path.
>> >
>> > If I run this algorithm on input with 1 million edges it never finishes,
>> > the
>> > master process and then the others always go out of memory, even with a
>> > 10GB
>> > heap. I know that java programs can be memory hungry, but 10GB heap for
>> > processing a 40MB input file is a bit to much in book. I have tried all
>> > sorts
>> > of settings, like disabling checkpoints, but nothing makes it finish. I
>> > also
>> > see a slowdown in processing, the first 20ish supersteps are done in no
>> > time,
>> > but then the processing slows down until it crashes in superstep 47.
>> >
>> > My questions are: What am I doing wrong? Do you guys have any pointers
>> > for
>> > things to look after? How can I get this thing to finish? Why is it so
>> > memory
>> > hungry?
>> >
>> > Thanks a lot for your help!
>> >
>> > -André
>>
>>
>>
>> --
>>    Claudio Martella
>>    claudio.martella@gmail.com



-- 
   Claudio Martella
   claudio.martella@gmail.com

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