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https://issues.apache.org/jira/browse/MAHOUT-960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13399366#comment-13399366
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Hudson commented on MAHOUT-960:
-------------------------------
Integrated in Mahout-Quality #1556 (See
[https://builds.apache.org/job/Mahout-Quality/1556/])
MAHOUT-960 Reduce memory usage of
ImplicitFeedbackAlternatingLeastSquaresSolver (Revision 1352796)
Result = SUCCESS
ssc : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1352796
Files :
*
/mahout/trunk/math/src/main/java/org/apache/mahout/math/als/ImplicitFeedbackAlternatingLeastSquaresSolver.java
> Reduce memory usage of ImplicitFeedbackAlternatingLeastSquaresSolver
> --------------------------------------------------------------------
>
> Key: MAHOUT-960
> URL: https://issues.apache.org/jira/browse/MAHOUT-960
> Project: Mahout
> Issue Type: Improvement
> Components: Collaborative Filtering
> Affects Versions: 0.6
> Reporter: Doug Mittendorf
> Assignee: Sebastian Schelter
> Priority: Minor
> Fix For: 0.8
>
> Attachments: MAHOUT-960-1.patch, MAHOUT-960.patch
>
>
> One of the main limiting factors of the implicit ALS algorithm when
> processing large datasets is the fact that it must fit the entire U or M
> matrix in memory. This is further compounded by the fact that the current
> implementation represents the matrix in memory 3 times:
> 1. As an OpenIntObjectHashMap read in from disk
> 2. A sorted DenseMatrix representation of #1 to prepare for computing Y'Y
> 3. The transpose of #2 (another DenseMatrix)
> The #3 copy of the matrix can be eliminated by computing Y'Y directly from Y
> without first computing the transpose of Y as an intermediate step. This
> should also be more efficient in terms of CPU usage.
> Note that the #1 copy of the matrix could also be eliminated if it's assumed
> that the user and item IDs are sequentially assigned and ordered. This would
> allow the DenseMatrix to be populated directly from disk instead of reading
> into an intermediate OpenIntObjectHashMap.
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