hadoop-azure and hadoop-azure-datalake have its own implementation of getFileBlockLocations(), which faked a list of artificial blocks based on the hard-coded block size. And each block has one host with name "localhost". Take a look at this code:
This is a unnecessary mock up for a "remote" file system to mimic HDFS. And the problem with this mock is that for large (~TB) files we generates lots of artificial blocks, and FileInputFormat.getSplits() is slow in calculating splits based on these blocks.
We can safely remove this customized getFileBlockLocations() implementation, fall back to the default FileSystem.getFileBlockLocations() implementation, which is to return 1 block for any file with 1 host "localhost". Note that this doesn't mean we will create much less splits, because the number of splits is still limited by the blockSize in FileInputFormat.computeSplitSize():