星火RDD中的分区数

Question

我通过指定分区数来从文本文件创建一个RDD (Spark1.6)。但是它给出了与指定分区不同的分区数。

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.txt的内容如下：

这是一个测试文件。将用于rdd分区。

基于上述情况，我有几个问题。

1. 对于例2，显式指定的分区数为0，但实际分区数为1(甚至默认最小分区数为2)，为什么实际分区数为1？
2. 对于第3种情况，为什么在指定的分区数上的实际分区数更改为+1？
3. 对于第4种情况，为什么在指定的分区数上的实际分区数更改为+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. 如果输入数据的大小很小(这可以很容易地安装到单个分区中)，那么为什么single会创建空分区呢？

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。

你要输入的那个号码叫做minSplits。它对最小分区数有影响，仅此而已。

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

分裂的数目应由getSplits方法(文档)来控制。

这个所以贴应该回答问题5