Spark: Why some tasks have zero input size. How is the input size calculated?

I am running 2 spark jobs with one performer and another with 8 performers.

A (1 performer)

spark-submit --class com.SmallfilesResearchProcess --master yarn-cluster --queue xxx --executor-memory 1g --driver-memory 6g --num-executors 1 --conf spark.executor.cores=8 --conf spark.logLineage=true /tmp/hadoop-tools-1.2-SNAPSHOT-spark.jar coalesce.num.partitions=32

      

        
        
        
      

    

Here are the results for case A from UI spark

Executor ID ▴   Address         Task Time   Total Tasks     Failed Tasks    Succeeded Tasks     Input Size / Records
1               machine:xxx     2.0 min        32             0              32                 404.5 MB / 525572

Total Time Across All Tasks: 2.0 min
Locality Level Summary: Node local: 1; Rack local: 31
Input Size / Records: 404.5 MB / 525572

      

        
        
        
      

    

B (8 performers)

spark-submit --class com.SmallfilesResearchProcess --master yarn-cluster --queue xxx --executor-memory 1g --driver-memory 6g --num-executors 8 --conf spark.executor.cores=8 --conf spark.logLineage=true /tmp/hadoop-tools-1.2-SNAPSHOT-spark.jar coalesce.num.partitions=32

      

        
        
        
      

    

Here are the results for case B from the UI spark

Executor ID ▴   Address         Task Time   Total Tasks     Failed Tasks    Succeeded Tasks     Input Size / Records
1               machine:xxxx    22 s        4                   0               4                   37.0 MB / 63106
2               machine:xxxx    25 s        4                   0               4                   0.0 B / 64068
3               machine:xxxx    27 s        4                   0               4                   0.0 B / 65045
4               machine:xxxx    22 s        4                   0               4                   38.1 MB / 64255
5               machine:xxxx    27 s        5                   0               5                   52.3 MB / 82091
6               machine:xxxx    22 s        5                   0               5                   49.1 MB / 79232
7               machine:xxxx    19 s        3                   0               3                   0.0 B / 48337
8               machine:xxxx    22 s        3                   0               3                   0.0 B / 59438


Total Time Across All Tasks: 2.8 min
Locality Level Summary: Node local: 4; Rack local: 28
Input Size / Records: 176.5 MB / 525572

      

        
        
        
      

    

Question 1: How is the size of the input calculated, I thought it should be the same, given that the entries are the same for both cases? 176.5 MB in case B versus 405 MB in case A.

Question 2: Why is the input size 0 B for some problems in case B?