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From David Garcia <dgar...@potomacfusion.com>
Subject RE: Resources or advice on minimising memory usage in Giraph/Hadoop code ?
Date Thu, 07 Jun 2012 14:30:11 GMT
it will if you have a fully connected graph, and/or your computation "requires" the instantiation
of all the vertices.  It's obviously not fully-connected since there are 2million vertices
and 4million edges. . .so unless all the vertices need to execute a computation, for whatever
reason, it may not be necessary to instantiate them all.
________________________________________
From: Claudio Martella [claudio.martella@gmail.com]
Sent: Thursday, June 07, 2012 1:35 AM
To: user@giraph.apache.org
Subject: Re: Resources or advice on minimising memory usage in Giraph/Hadoop code ?

Won't this just postpone the pain?

On Thursday, June 7, 2012, David Garcia wrote:
Based upon what you have mentioned, o think you are getting heap errors because every vertex
in your graph will be loaded into memory prior to super step one.  So if you have a large
graph, with lots of state, you probably have memory issues from the very beginning.  A simple
way to mitigate the problem is to simply load the vertices that you need and then add vertices
as your computation progresses.  This will prevent the entire graph from occupying memory.

Sent from my HTC Inspireā„¢ 4G on AT&T

----- Reply message -----
From: "Avery Ching" <aching@apache.org<javascript:_e({},%20'cvml',%20'aching@apache.org');>>
To: "user@giraph.apache.org<javascript:_e({},%20'cvml',%20'user@giraph.apache.org');>"
<user@giraph.apache.org<javascript:_e({},%20'cvml',%20'user@giraph.apache.org');>>
Subject: Resources or advice on minimising memory usage in Giraph/Hadoop code ?
Date: Wed, Jun 6, 2012 10:33 pm



No article or book, but here's a few tips.

1) Use aggregators!  This can drastically can reduce the amount of
memory use by combining messages on the server side.
2) -Dmapred.child.java.opts="-Xss128k" or some other value (should
affect the RPC threads or netty threads)
3) You'll want to minimize the state of every vertex as best as
possible, perhaps creating a custom vertex.

Avery

On 6/5/12 7:38 PM, Benjamin Heitmann wrote:
> Hello,
>
> can somebody recommend a web page, article or book on minimising the memory usage of
Giraph/Hadoop code ?
> I am looking for non-obvious advice on what *not* to do, and for best practices on what
to do inside of Hadoop...
>
> E.g. is it preferable to use Java Strings or Hadoop Text Writables ? Should all strings
be externalised ?
>
> Currently, I am running a Giraph job with 10 workers. Each worker has a maximum heap
of Xmx7G.
> The concurrent garbage collection is enabled. The machine has 24 cores, and 96 GB of
memory.
> The job currently uses a max of around 50 GB, so there is free memory available outside
of java.
>
> The graph itself has ~2 million vertices and ~4 million edges, which is not really "big
data".
>
> However, before starting superstep 1, I get heap space errors. Previous versions of my
algorithm where simpler,
> but they also ran into heap space errors when the data was around one order of magnitude
bigger.
>
> My suspicion is that the amount of state which my vertices have, and the amount of messages
which I am generating
> exceeds the standard use case of a pagerank rank algorithm by far.
>
> To list a few of the reasons why I need a lot of state:
>
> * I need to execute multiple runs of the same algorithm in parallel. Loading this specific
graph takes about 3 minutes,
> running the algorithm once takes about 10 seconds or so, but I have around 600 users
in that graph. And this is just a small graph,
> the whole algorithm is intended to be run for thousands of users. (... "big data"...)
>
> * The identities of the edges and vertices are not based on numbers but on strings.
> All edges and all vertices have a URI associated with them.
> The graph represents RDF data from different sources, such as DBpedia.
> In addition, most of the vertices have one or multiple types associated with them, and
> each type is again represented by a URI.
> These types are essential to the logic of the algorithm.
> I guess it would be possible to externalise all of those strings, but it adds a layer
of complexity which I had previously hoped to avoid.
>
> * As Giraph does not currently provide a central coordination point for the processing
of the graph,
> I need to send a lot of messages between vertices in order to coordinate the algorithm.
>
> * Giraph does not allow multiple Java classes to be used for different vertices in the
same graph.
> However, different vertices have different roles in my algorithm, and each role has a
different set of states in which it can be,
> due to the missing global coordination point.
>
> * Taken together, the lack of a central coordination point and the inabiltity to have
different java classes as part of the same graph,
> make the whole algorithm more similar to a network protocol and not to a graph algorithm.
Thus I need a lot of messages
> and a lot of state.
>
>
> If anybody has some good suggestion on how I should proceed, I would be very interested
in hearing them.
>
> If somebody wants to take a look at my code, then I can currently provide you with that
code in a non-public way.
>
> sincerely, Benjamin Heitmann.
>



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

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