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From "Maja Kabiljo (JIRA)" <>
Subject [jira] [Commented] (GIRAPH-322) Run Length Encoding for Vertex#sendMessageToAllEdges might curb out of control message growth in large scale jobs
Date Tue, 11 Sep 2012 14:59:07 GMT


Maja Kabiljo commented on GIRAPH-322:

You are missing the default constructor for SendBroadcastMessageRequest. If you are testing
it with smaller example it can be the cause of the problem you described, since flush will
be the first moment when messages get sent and processed. Though you should be able to see
the exception if this is the only problem. 

Great work, I'm looking forward to hear how it performs.

This is not a big deal, but when sendBroadcastMessageRequest is called you have all destinations
grouped together, and then you add it one by one to the cache where they are grouped together

Revisiting out-of-core to work better with this solution is not going to be straightforward,
since we still want to keep the messages for one vertex grouped together in order to minimize
random accesses. I'll think a bit about it and share anything I came up with.

One thing that doesn't seem good is that you are setting the number of partitions to 1 per
worker. I think Avery already suggested something about modifying SendMessageCache to keep
and send messages per worker, not per partition. So something like that could also be done
with this solution.

Was your plan to use out-of-core graph in the end also, or that data would fit in memory?

I'm really interested in hearing whether you make it work with out-of-core messages. I agree
with what you said for benchmarks vs real use cases, but for out-of-core messages I don't
see how it can get worse than RandomMessageBenchmark since one can't generate messages at
higher rate than there :-) Maybe memory is leaking elsewhere, one thing you can try is set
number of in-core messages and open requests to something really low, it will be extremely
slow but just to see whether it will crash.
> Run Length Encoding for Vertex#sendMessageToAllEdges might curb out of control message
growth in large scale jobs
> -----------------------------------------------------------------------------------------------------------------
>                 Key: GIRAPH-322
>                 URL:
>             Project: Giraph
>          Issue Type: Improvement
>          Components: bsp
>    Affects Versions: 0.2.0
>            Reporter: Eli Reisman
>            Assignee: Eli Reisman
>            Priority: Minor
>             Fix For: 0.2.0
>         Attachments: GIRAPH-322-1.patch, GIRAPH-322-2.patch
> Vertex#sendMessageToAllEdges is a case that goes against the grain of the data structures
and code paths used to transport messages through a Giraph application and out on the network.
While messages to a single vertex can be combined (and should be) in some applications that
could make use of this broadcast messaging, the out of control message growth of algorithms
like triangle closing means we need to de-duplicate messages bound for many vertices/partitions.
> This will be an evolving solution (this first patch is just the first step) and currently
it does not present a robust solution for disk-spill message stores. I figure I can get some
advice about that or it can be a follow-up JIRA if this turns out to be a fruitful pursuit.
This first patch is also Netty-only and simply defaults to the old sendMessagesToAllEdges()
implementation if USE_NETTY is false. All this can be cleaned up when we know this works and/or
is worth pursuing.
> The idea is to send as few broadcast messages as possible by run-length encoding their
delivery and only duplicating message on the network when they are bound for different partitions.
This is also best when combined with "-Dhash.userPartitionCount=# of workers" so you don't
do too much of that.
> If this shows promise I will report back and keep working on this. As it is, it represents
an end-to-end solution, using Netty, for in-memory messaging. It won't break with spill to
disk, but you do lose the de-duplicating effect.
> More to follow, comments/ideas welcome. I expect this to change a lot as I test it and
ideas/suggestions crop up.

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