Spark number of tasks (partitions) is not equal to spark.default.parallelism - apache-spark

Question

I build a spark cluster and submit application with standalone mode. My application only contains one stage, which read data from HDFS.
In some posts, it is recommended to set spark.default.parallelism parameters to 2~3 times to number of cores. In this sense, I set this parameters to 300 so that there are 300 partitions/tasks in each stage.
However, when I check the log, I find something like
Finished task 133.1 in stage 0.0 (TID 157) in 22236 ms on 166.111.74.114 (executor 1) (147/147)
I have some problems about this log:
Why my total task number is 147, instead of 300. I have checked Enviroment in master:18080, and the value of spark.conf.parallelism is 300 for sure.
Why is it "finished task 133.1", i.e., what does ".1" stand for?
I post the code that I used in the following. It simply filter rows that contains "target word".
package com.sparkApp
import org.apache.spark.{SparkConf, SparkContext}
object MyClass {
def main(args: Array[String]): Unit = {
val sparkConf = new SparkConf()
.setMaster("spark://master:7077")
.setAppName("FilterRow")
val sc = new SparkContext(sparkConf);
val targetWord = "target word"
val lines = sc.textFile("hdfs://master:9000/path-to-input")
val items = lines.filter(x => x.split("\t").size >= 4)
.map(x => x.split("\t")(3))
.filter(x => x.contains(targetWord))
.saveAsTextFile("hdfs://master:9000/path-to-output")
sc.stop()
}
}
I use the following submit command:
bin/spark-submit \
--class com.sparkApp.MyClass \
--master spark://master:7077 \
--executor-cores 4 \
--total-executor-cores 20 \
--executor-memory 4G \
--conf spark.default.parallelism=300 \
/path/to/SparkApp.jar
I also paste part of logging information:
21/08/18 00:40:48 INFO TaskSetManager: Starting task 17.0 in stage 0.0 (TID 20, 166.111.74.126, executor 3, partition 17, ANY, 7450 bytes)
21/08/18 00:40:48 INFO TaskSetManager: Finished task 66.0 in stage 0.0 (TID 3) in 5007 ms on 166.111.74.126 (executor 3) (1/147)
21/08/18 00:40:48 INFO TaskSetManager: Starting task 18.0 in stage 0.0 (TID 21, 166.111.74.114, executor 1, partition 18, ANY, 7450 bytes)
21/08/18 00:40:48 INFO TaskSetManager: Finished task 15.0 in stage 0.0 (TID 18) in 1859 ms on 166.111.74.114 (executor 1) (2/147)
21/08/18 00:40:48 INFO TaskSetManager: Starting task 19.0 in stage 0.0 (TID 22, 166.111.74.126, executor 3, partition 19, ANY, 7450 bytes)
21/08/18 00:40:48 INFO TaskSetManager: Finished task 53.0 in stage 0.0 (TID 2) in 5408 ms on 166.111.74.126 (executor 3) (3/147)
...
21/08/18 00:41:51 INFO TaskSetManager: Starting task 146.2 in stage 0.0 (TID 158, 166.111.74.114, executor 2, partition 146, ANY, 7447 bytes)
21/08/18 00:41:55 INFO TaskSetManager: Finished task 146.2 in stage 0.0 (TID 158) in 3560 ms on 166.111.74.114 (executor 2) (146/147)
21/08/18 00:41:59 INFO TaskSetManager: Finished task 133.1 in stage 0.0 (TID 157) in 22236 ms on 166.111.74.114 (executor 1) (147/147)
Thanks ahead for your patience on this question.