[jira] [Created] (SPARK-14371) OnlineLDAOptimizer should not collect stats for each doc in mini-batch to driver

["Joseph K. Bradley (JIRA)" <ji...@apache.org>]

Joseph K. Bradley created SPARK-14371:
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             Summary: OnlineLDAOptimizer should not collect stats for each doc in mini-batch to driver
                 Key: SPARK-14371
                 URL: https://issues.apache.org/jira/browse/SPARK-14371
             Project: Spark
          Issue Type: Improvement
          Components: MLlib
            Reporter: Joseph K. Bradley
            Priority: Minor


See this line: https://github.com/apache/spark/blob/5743c6476dbef50852b7f9873112a2d299966ebd/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAOptimizer.scala#L437

The second element in each row of "stats" is a list with one Vector for each document in the mini-batch.  Those are collected to the driver in this line:
https://github.com/apache/spark/blob/5743c6476dbef50852b7f9873112a2d299966ebd/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAOptimizer.scala#L456

We should not collect those to the driver.  Rather, we should do the necessary maps and aggregations in a distributed manner.  This will involve modify the Dirichlet expectation implementation.  (This JIRA should be done by someone knowledge about online LDA and Spark.)



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