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https://issues.apache.org/jira/browse/MAHOUT-473?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898093#action_12898093
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Sebastian Schelter commented on MAHOUT-473:
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Hui,
Can you follow these steps on this issue:
# Modify your local copy of mahout to include the changes you propose
# build Mahout and run your job again with your modified version
# upload a patch containing your changes and give us some details on the
performance increase you encountered
Have a look at this website:
https://cwiki.apache.org/confluence/display/MAHOUT/How+To+Contribute
> add parameter -Dmapred.reduce.tasks when call job RowSimilarityJob in
> RecommenderJob
> ------------------------------------------------------------------------------------
>
> Key: MAHOUT-473
> URL: https://issues.apache.org/jira/browse/MAHOUT-473
> Project: Mahout
> Issue Type: Improvement
> Components: Collaborative Filtering
> Affects Versions: 0.4
> Reporter: Han Hui Wen
> Fix For: 0.4
>
> Attachments: screenshot-1.jpg
>
>
> In RecommenderJob
> {code:title=RecommenderJob.java|borderStyle=solid}
> int numberOfUsers = TasteHadoopUtils.readIntFromFile(getConf(),
> countUsersPath);
> if (shouldRunNextPhase(parsedArgs, currentPhase)) {
> /* Once DistributedRowMatrix uses the hadoop 0.20 API, we should
> refactor this call to something like
> * new DistributedRowMatrix(...).rowSimilarity(...) */
> try {
> RowSimilarityJob.main(new String[] { "-Dmapred.input.dir=" +
> maybePruneItemUserMatrixPath.toString(),
> "-Dmapred.output.dir=" + similarityMatrixPath.toString(),
> "--numberOfColumns",
> String.valueOf(numberOfUsers), "--similarityClassname",
> similarityClassname, "--maxSimilaritiesPerRow",
> String.valueOf(maxSimilaritiesPerItemConsidered + 1),
> "--tempDir", tempDirPath.toString() });
> } catch (Exception e) {
> throw new IllegalStateException("item-item-similarity computation
> failed", e);
> }
> }
> {code}
> We have not passed parameter -Dmapred.reduce.tasks when job RowSimilarityJob.
> It caused all three RowSimilarityJob sub-jobs run using 1 map and 1 reduce,
> so the sub jobs can not be scalable.
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