Github user hqzizania commented on the issue: https://github.com/apache/spark/pull/13891 @yanboliang So sorry for my late response. Some regression performance test results: Datasets: using [genExplicitTestData](https://github.com/apache/spark/pull/13891/files#diff-2c1dd810bcfabf444a0ecdcd613e954aR393) to generate with numUsers = 20000, numItems = 2000 Single-node cluster: 16 physical cores, 100GB memory ALS: numUserBlocks = 30, numItemBlocks = 30 It will run [computeFactors](https://github.com/apache/spark/pull/13891/files#diff-be65dd1d6adc53138156641b610fcadaR1291) with 30 partitions in parallel. ==================================================== ALS: rank = 1024 Computing time and used memory for computeFactors: ![image](https://cloud.githubusercontent.com/assets/9315372/19587668/cb0065a8-9792-11e6-8226-b5a448a8dc9a.png) ===================================================== ALS: rank = 129 Computing time for computeFactors: ![image](https://cloud.githubusercontent.com/assets/9315372/19587672/d0197d54-9792-11e6-86df-b260d165c8e6.png) ===================================================== ALS: rank = 512 Computing time for computeFactors: ![image](https://cloud.githubusercontent.com/assets/9315372/19587680/d542783a-9792-11e6-95a2-c2001eb59853.png) The results shows this patch makes it faster very much when rank is large, but we should reset the two threshold values of "doStack". However, a following problem is that the unit test for this patch will take much time as rank must be larger than 1024. Should I just remove the unit test?
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