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From "Alessandro Presta (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-357) Don't try to combine if there is only one message
Date Fri, 05 Oct 2012 17:52:03 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13470502#comment-13470502
] 

Alessandro Presta commented on GIRAPH-357:
------------------------------------------

As per offline discussion, it would be interesting to evaluate the impact of combining on
client, server or both.
We may find out, for example, that it's not worth it on the client, while on the server it
may help to combine every X messages (just a hypothesis).

Also regarding the possibility of serializing straight away (which is doable if we drop combining),
we have to be careful: it may give a speedup in some cases, but penalize us in some others
since we can't reuse objects effectively.
To give a concrete example, in some label propagation implementations the message data contains
a map that is sent to all neighbors. So all messages share that reference, as opposed to making
copies of the map.
                
> Don't try to combine if there is only one message
> -------------------------------------------------
>
>                 Key: GIRAPH-357
>                 URL: https://issues.apache.org/jira/browse/GIRAPH-357
>             Project: Giraph
>          Issue Type: Improvement
>            Reporter: Maja Kabiljo
>            Assignee: Maja Kabiljo
>         Attachments: GIRAPH-357.patch
>
>
> In SendMessageCache, we call combiner even if we have just one message. Combining is
kind of expensive since we recreate the message object and the list. With default settings
and bigger graph, for PageRankBenchmark there is 10-15% superstep speedup if we don't call
it when we have a single message.

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