When running on blobstores (like S3) where metadata operations (like listStatus) are costly, Utilities.getInputPaths() can add significant overhead when setting up the input paths for an MR / Spark / Tez job.
The method performs a listStatus on all input paths in order to check if the path is empty. If the path is empty, a dummy file is created for the given partition. This is all done sequentially. This can be really slow when there are a lot of empty partitions. Even when all partitions have input data, this can take a long time.
We should either:
(1) Just remove the logic to check if each input path is empty, and handle any edge cases accordingly.
(2) Multi-thread the listStatus calls