Minor Description
the disk buffers created in s3a and abfs output streams use a simple String.format("datablock-%04d-", index) pattern for the prefix for File.tmpFile
this means there will be contention for filenames across streams, especially across processes.
if each stream had a uuid prefix there'd be no contention. That'd change the API though. Alternatively: each disk block factory has the uuid, and the index is simply total number blocks created.