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From "Wang, Jensen" <>
Subject defaultMinPartitions in textFile
Date Tue, 22 Jul 2014 02:18:15 GMT
        I started to use spark on yarn recently and found a problem while tuning my program.

When SparkContext is initialized as sc and ready to read text file from hdfs, the textFile(path,
defaultMinPartitions) method is called.
I traced down the second parameter in the spark source code and finally found this:
   conf.getInt("spark.default.parallelism", math.max(totalCoreCount.get(), 2))  in  CoarseGrainedSchedulerBackend.scala

I do not specify the property "spark.default.parallelism" anywhere so the getInt will return
value from the larger one between totalCoreCount and 2.

When I submit the application using spark-submit and specify the parameter: --num-executors
 2   --executor-cores 6, I suppose the totalCoreCount will be
2*6 = 12, so defaultMinPartitions will be 12.

But when I print the value of defaultMinPartitions in my program, I still get 2 in return,
 How does this happen, or where do I make a mistake?

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