As more hashes arrive at the server, the server is able to
decide which peers (mappers) have the correct intermediate
files. This information is placed at the BitTorrent tracker and
a new .torrent file is created publishing where future volunteers
playing the reduce role can find this intermediate output.
When all the intermediate outputs are available, the scheduler
starts issuing reducer tasks. These reducer tasks have a reference
to the .torrent files that need to be downloaded. Once a
reducer has access to these .torrent files, it starts transferring
the intermediate files (using the BitTorrent protocol) from all
the mappers that completed the map task with success (the
ones that were successfully validated). Reduce tasks start as
soon as all the needed intermediate values are successfully
transfered.