火花RDD中的分区数

Question

我通过指定分区的数量从文本文件创建RDD（Spark 1.6）。但它给我的分区数与指定的分区数不同。

案例1

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 1)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[50] at textFile at <console>:27

scala> people.getNumPartitions
res36: Int = 1

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 2)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[52] at textFile at <console>:27

scala> people.getNumPartitions
res37: Int = 2

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 3)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[54] at textFile at <console>:27

scala> people.getNumPartitions
res38: Int = 3

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 4)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[56] at textFile at <console>:27

scala> people.getNumPartitions
res39: Int = 4

案例2

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 0)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[72] at textFile at <console>:27

scala> people.getNumPartitions
res47: Int = 1

案例3

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 5)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[58] at textFile at <console>:27

scala> people.getNumPartitions
res40: Int = 6

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 6)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[60] at textFile at <console>:27

scala> people.getNumPartitions
res41: Int = 7

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 7)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[62] at textFile at <console>:27

scala> people.getNumPartitions
res42: Int = 8

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 8)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[64] at textFile at <console>:27

scala> people.getNumPartitions
res43: Int = 9

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 10)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[68] at textFile at <console>:27

scala> people.getNumPartitions
res45: Int = 11

案例4

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 9)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[66] at textFile at <console>:27

scala> people.getNumPartitions
res44: Int = 11

scala> val people = sc.textFile("file:///home/pvikash/data/test.txt", 11)
people: org.apache.spark.rdd.RDD[String] = MapPartitionsRDD[70] at textFile at <console>:27

scala> people.getNumPartitions
res46: Int = 13

文件/home/pvikash/data/test的内容。txt是：

这是一个测试文件。将用于rdd分区

基于以上案例，我有几个问题。

1. 对于案例2，显式指定的分区数为0，但实际分区数为1（即使默认最小分区为2），为什么实际分区数为1？
2. 对于案例3，为什么在指定数量的分区上实际分区数更改了1？
3. 对于案例4，为什么在指定数量的分区上实际分区数更改了2？
4. 为什么火花在案例1、案例2、案例3和案例4中表现不同？
5. 如果输入数据很小（可以很容易地放入单个分区），那么为什么Spark会创建空分区？

任何解释都将不胜感激。

Answer 1

不是一个完整的答案，但它可能会让你更接近它。

您传入的数字称为minSplits。它对最小分区数有影响，仅此而已。

def textFile(path: String, minSplits: Int = defaultMinSplits): RDD[String]

拆分数量应由< code>getSplits方法(docs)控制

这篇SO帖子应该回答问题5