[DEBUGGING] Huge amount of tasks when writing files into HDFS

I am using the manual build master after https://github.com/apache/incubator-hudi/commit/36b3b6f5dd913d3f1c9aa116aff8daf6540fed65 commit. EDIT: tried with the latest master but got the same result

I am seeing 3 million tasks when the Hudi Spark job writing the files into HDFS. It seems like related to the input size. With 7.7 GB input it was 3.2 million tasks, with 9 GB input it was 3.7 million. Both with 10 parallelisms. 

I am seeing a huge amount of 0 byte files being written into .hoodie/.temp/ folder in my HDFS. In the Spark UI, each task only writes less than 10 records in

count at HoodieSparkSqlWriter

 All the stages before this seem normal. Any idea what happened here? My first guess would be something related to the bloom filter index. Maybe somewhere trigger the repartitioning with the bloom filter index? But I am not really familiar with that part of the code. 

Thanks