The consequence is that mapreduce probably is not splitting s3a files in the expected way. This is similar to
HADOOP-5861 (which was for s3n, though s3n was passing 5G rather than 0 for block size).
FileInputFormat.getSplits() relies on the FileStatus block size being set:
However, S3AFileSystem does not set the FileStatus block size field. From S3AFileStatus.java:
I think it should use S3AFileSystem.getDefaultBlockSize() for each file's block size (where it's currently passing 0).