> coalesce(1,shuffle = true)
> coalesce(1,shuffle = false)

代码示例：

val input = sc.textFile(inputFile)
val filtered = input.filter(doSomeFiltering)
val mapped = filtered.map(doSomeMapping)

mapped.coalesce(1,shuffle = true).saveAsTextFile(outputFile)
vs
mapped.coalesce(1,shuffle = false).saveAsTextFile(outputFile)

它与collect()相比如何？我完全知道Spark保存方法会将它存储为HDFS风格的结构,但是我对collect()和shuffled / non-shuffled coalesce()的数据分区方面更感兴趣.