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https://issues.apache.org/jira/browse/MAHOUT-1469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13982470#comment-13982470
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Ted Dunning commented on MAHOUT-1469:
-------------------------------------
[~arapmv]
There is a known bottle neck in the parallel version due to the fact that if
you split the computation m ways, each split has to produce k log N/m sketch
clusters for a total of mk log N/m clusters passed to the reducers. If k =
1000 and you have m=1000 mappers, then processing a billion points will produce
20,000 sketch clusters from each mapper and you will potentially have
20,000,000 centroids passed to the reducer which is only 50x less than the
original data size. Some map-reduce implementations have per-JVM combiners
(MapR, for one, can't say about others) which could make things a bit better,
but the basic problem is still there.
Regarding the separation of the different phases, I think that this is already
available in the code. That is, the streaming k-means is independent of the
kmeans++ / ball k-means step. I don't think that the k-means++ (ish)
initialization is available separately, but that would be pretty easy to do.
> Streaming KMeans fails when executed in MapReduce mode and
> REDUCE_STREAMING_KMEANS is set to true
> -------------------------------------------------------------------------------------------------
>
> Key: MAHOUT-1469
> URL: https://issues.apache.org/jira/browse/MAHOUT-1469
> Project: Mahout
> Issue Type: Bug
> Components: Clustering
> Affects Versions: 0.9
> Reporter: Suneel Marthi
> Assignee: Suneel Marthi
> Fix For: 1.0
>
>
> Centroids are not being generated when executed in MR mode with -rskm flag
> set.
> {Code}
> 14/03/20 02:42:12 INFO mapreduce.StreamingKMeansThread: Estimated Points: 282
> 14/03/20 02:42:12 INFO mapred.JobClient: map 100% reduce 0%
> 14/03/20 02:42:14 INFO mapreduce.StreamingKMeansReducer: Number of Centroids: > 0
> 14/03/20 02:42:14 WARN mapred.LocalJobRunner: job_local1374896815_0001
> java.lang.IllegalArgumentException: Must have nonzero number of training and
> test vectors. Asked for %.1f %% of %d vectors for test [10.000000149011612, 0]
> at
> com.google.common.base.Preconditions.checkArgument(Preconditions.java:148)
> at
> org.apache.mahout.clustering.streaming.cluster.BallKMeans.splitTrainTest(BallKMeans.java:176)
> at
> org.apache.mahout.clustering.streaming.cluster.BallKMeans.cluster(BallKMeans.java:192)
> at
> org.apache.mahout.clustering.streaming.mapreduce.StreamingKMeansReducer.getBestCentroids(StreamingKMeansReducer.java:107)
> at
> org.apache.mahout.clustering.streaming.mapreduce.StreamingKMeansReducer.reduce(StreamingKMeansReducer.java:73)
> at
> org.apache.mahout.clustering.streaming.mapreduce.StreamingKMeansReducer.reduce(StreamingKMeansReducer.java:37)
> at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:177)
> at
> org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:649)
> at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:418)
> at
> org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:398)
> 14/03/20 02:42:14 INFO mapred.JobClient: Job complete:
> job_local1374896815_0001
> 14/03/20 02:42:14 INFO mapred.JobClient: Counters: 16
> 14/03/20 02:42:14 INFO mapred.JobClient: File Input Format Counters
> 14/03/20 02:42:14 INFO mapred.JobClient: Bytes Read=17156391
> 14/03/20 02:42:14 INFO mapred.JobClient: FileSystemCounters
> 14/03/20 02:42:14 INFO mapred.JobClient: FILE_BYTES_READ=41925624
> 14/03/20 02:42:14 INFO mapred.JobClient: FILE_BYTES_WRITTEN=25974741
> 14/03/20 02:42:14 INFO mapred.JobClient: Map-Reduce Framework
> 14/03/20 02:42:14 INFO mapred.JobClient: Map output materialized
> bytes=956293
> 14/03/20 02:42:14 INFO mapred.JobClient: Map input records=21578
> 14/03/20 02:42:14 INFO mapred.JobClient: Reduce shuffle bytes=0
> 14/03/20 02:42:14 INFO mapred.JobClient: Spilled Records=282
> 14/03/20 02:42:14 INFO mapred.JobClient: Map output bytes=1788012
> 14/03/20 02:42:14 INFO mapred.JobClient: Total committed heap usage
> (bytes)=217214976
> 14/03/20 02:42:14 INFO mapred.JobClient: Combine input records=0
> 14/03/20 02:42:14 INFO mapred.JobClient: SPLIT_RAW_BYTES=163
> 14/03/20 02:42:14 INFO mapred.JobClient: Reduce input records=0
> 14/03/20 02:42:14 INFO mapred.JobClient: Reduce input groups=0
> 14/03/20 02:42:14 INFO mapred.JobClient: Combine output records=0
> 14/03/20 02:42:14 INFO mapred.JobClient: Reduce output records=0
> 14/03/20 02:42:14 INFO mapred.JobClient: Map output records=282
> 14/03/20 02:42:14 INFO driver.MahoutDriver: Program took 506269 ms (Minutes:
> 8.437816666666667)
> {Code}
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