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From Reinis Vicups <>
Subject Mahout 1.0: parallelism/number tasks during SimilarityAnalysis.rowSimilarity
Date Mon, 13 Oct 2014 15:56:13 GMT

I am currently testing SimilarityAnalysis.rowSimilarity and I am 
wondering, how could I increase number of tasks to use for distributed 

What I currently observe, is that SimilarityAnalysis is requiring almost 
20 minutes for my dataset only with this stage:

combineByKey at ABt.scala:126

When I view details for the stage I see that only one task is spawned 
running on one node.

I have my own implementation of SimilarityAnalysis and by tuning number 
of tasks I have reached HUGE performance gains.

Since I couldn't find how to pass the number of tasks to shuffle 
operations directly, I have set following in spark config

configuration = new SparkConf().setAppName(jobConfig.jobName)
         .set("spark.kryo.referenceTracking", "false")
         .set("spark.kryoserializer.buffer.mb", "200")
         .set("spark.default.parallelism", 400) // <- this is the line 
supposed to set default parallelism to some high number

Thank you for your help

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