Github user steveloughran commented on the issue:
https://github.com/apache/spark/pull/14038
Path filtering in Hadoop FS calls on anything other than filename is very
suboptimal; in #14731 you can see where the filtering has been postoned until
after the listing, when the full `FileStatus` entry list has been returned.
As filtering is the last operation in the various listFiles calls, there's
no penalty to doing the filtering after the results come in. In
`FileSytem.globStatus()` the filtering takes place after the glob match, but
during the scan...a larger list will be built and returned, but that is all.
I think a new filter should be executed after these operations, taking the
`FileStatus` object, this provides a superset of filtering possible within the
Hadoop calls (timestamp, filetype, ...), with no performance penalty. It's more
flexible than the simple `accept(path)`, and will guarantee that nobody using
the API will implement a suboptimal filter.
Consider also taking a predicate `Filesystem => Boolean`, rather than
requiring callers to implement new classes. It can be fed straight into
`Iterator.filter()`.
I note you are making extensive use of `listLeafFiles`; that's a
potentially inefficent implementation against object stores. Keep using it
âI'll patch it to use `FileSystem.listFiles(path, true)` for in FS recursion
and O(files/5000) listing against S3A in Hadoop 2.8; eventually Azure and swoft
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