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https://issues.apache.org/jira/browse/MAHOUT-1035?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sebastian Schelter resolved MAHOUT-1035.
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Resolution: Fixed
> Hotspot in recommenditembased – UnsymmetrifyMapper job
> ------------------------------------------------------
>
> Key: MAHOUT-1035
> URL: https://issues.apache.org/jira/browse/MAHOUT-1035
> Project: Mahout
> Issue Type: Improvement
> Components: Collaborative Filtering
> Affects Versions: 0.7
> Reporter: Bhaskar Devireddy
> Assignee: Sebastian Schelter
> Priority: Minor
> Fix For: 0.8
>
> Attachments: MAHOUT-1035.patch, patch_1035.patch,
> patch_1035_ver2.patch
>
>
> While profiling the unsymmetrify mapper job in recommendations we noticed an
> hotspot consuming 90% of the CPU runtime in
> org.apache.mahout.math.map.OpenIntDoubleHashMap.keys method for the first map
> task. We used the script provided in mahout examples for running ASF Email
> recommendations for profiling. The attached patch addresses the hotspot by
> reducing the number of for loop iterations in OpenIntDoubleHashMap.keys
> method by changing the initialization of transposedPartial. This patch while
> retaining functionality(verified the output with and without patch) speeds up
> the unsymmetrify mapper task by more than 4X on x86 architectures.
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