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https://issues.apache.org/jira/browse/MAHOUT-475?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen updated MAHOUT-475:
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Status: Resolved (was: Patch Available)
Assignee: Sean Owen
Resolution: Not A Problem
People can 'correct' me here but conceptually Mappers and Reducers are single
threaded. It's up to a Hadoop cluster to run multiple workers per machine to
take advantage of more cores and parallelism.
> Replace Mapper with MultithreadedMapper to run job pairwiseSimilarity
> ------------------------------------------------------------------------
>
> Key: MAHOUT-475
> URL: https://issues.apache.org/jira/browse/MAHOUT-475
> Project: Mahout
> Issue Type: Improvement
> Components: Collaborative Filtering
> Affects Versions: 0.4
> Reporter: Han Hui Wen
> Assignee: Sean Owen
> Fix For: 0.4
>
> Attachments: patch_985097.txt
>
>
> Because CooccurrencesMapper has huge computing,
> Maybe we can replace Mapper with MultithreadedMapper.
> And call the mapper
> original:
> {code}
> if (shouldRunNextPhase(parsedArgs, currentPhase)) {
> Job pairwiseSimilarity = prepareJob(weightsPath,
> pairwiseSimilarityPath,
> SequenceFileInputFormat.class,
> CooccurrencesMapper.class,
> WeightedRowPair.class,
> Cooccurrence.class,
> SimilarityReducer.class,
> SimilarityMatrixEntryKey.class,
> MatrixEntryWritable.class,
> SequenceFileOutputFormat.class);
> Configuration pairwiseConf = pairwiseSimilarity.getConfiguration();
> pairwiseConf.set(DISTRIBUTED_SIMILARITY_CLASSNAME,
> distributedSimilarityClassname);
> pairwiseConf.setInt(NUMBER_OF_COLUMNS, numberOfColumns);
> pairwiseSimilarity.waitForCompletion(true);
> }
> {code}
> new:
> {code}
> if (shouldRunNextPhase(parsedArgs, currentPhase)) {
> Job pairwiseSimilarity = prepareJob(weightsPath,
> pairwiseSimilarityPath,
> SequenceFileInputFormat.class,
> CooccurrencesMapper.class,
> WeightedRowPair.class,
> Cooccurrence.class,
> SimilarityReducer.class,
> SimilarityMatrixEntryKey.class,
> MatrixEntryWritable.class,
> SequenceFileOutputFormat.class);
>
> Configuration pairwiseConf = pairwiseSimilarity.getConfiguration();
> pairwiseConf.set(DISTRIBUTED_SIMILARITY_CLASSNAME,
> distributedSimilarityClassname);
> pairwiseConf.setInt(NUMBER_OF_COLUMNS, numberOfColumns);
> MultithreadedMapper.setMapperClass(pairwiseSimilarity,
> CooccurrencesMapper.class);
> MultithreadedMapper.setNumberOfThreads(pairwiseSimilarity,
> numMapThreads);
> SequenceFileOutputFormat.setCompressOutput(pairwiseSimilarity, true);
> SequenceFileOutputFormat.setOutputCompressorClass(pairwiseSimilarity,
> GzipCodec.class);
> SequenceFileOutputFormat.setOutputCompressionType(pairwiseSimilarity,
> CompressionType.BLOCK);
> pairwiseSimilarity.waitForCompletion(true);
> }
> {code}
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