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From "Avery Ching (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-124) Combiner should return Iterable<M> instead of M or null.
Date Sat, 21 Jan 2012 08:40:40 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13190351#comment-13190351
] 

Avery Ching commented on GIRAPH-124:
------------------------------------

Nice, Claudio.  I haven't had a chance to fully test it, but wanted to give you some early
feedback.

1)  Some changes have messed up indenting a little (here are some examples)

-        public FloatWritable combine(LongWritable vertexIndex,
+        public Iterable<FloatWritable> combine(LongWritable vertexIndex,
                                   Iterable<FloatWritable> msgList)

-   public abstract M combine(I vertexIndex,
+   public abstract Iterable<M> combine(I vertexIndex,
                              Iterable<M> messages) throws IOException;

-                        M combinedMsg = combiner.combine(entry.getKey(),
+                        Iterable<M> messages = combiner.combine(entry.getKey(),
                                                          entry.getValue());

-    public IntWritable combine(LongWritable vertexIndex,
+    public Iterable<IntWritable> combine(LongWritable vertexIndex,
                                Iterable<IntWritable> messages)

2)  Should we make the requirement that the returned result has a size < input size?  I
think the argument was that some classification of messages might not always reduce the number
of messages?  Perhaps <=?
                
> Combiner should return Iterable<M> instead of M or null.
> --------------------------------------------------------
>
>                 Key: GIRAPH-124
>                 URL: https://issues.apache.org/jira/browse/GIRAPH-124
>             Project: Giraph
>          Issue Type: Improvement
>          Components: graph
>    Affects Versions: 0.1.0
>            Reporter: Claudio Martella
>         Attachments: GIRAPH-124.diff
>
>
> Currently VertexCombiner is expected to return a single message combining the input messages,
or null in case no message should be sent. The new expected interface should return an Iterable<M>,
possibly empty. The number of elements in the returned Iterable is supposed to be smaller
than the number of input messages, by the initial definition of a Combiner (defined as a function
to reduce I/O by combining multiple messages into 1).

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