[vox-tech] bittorrent - no seeds but distributed copies increase

[Rob Rogers]

On Mon, Jul 26, 2004 at 03:32:08PM -0700, Ken Bloom wrote:
> Hi, Pete,
>    My research project this summer concerns BitTorrent. (Although I'm
> currently working on the choking algorithm, not the piece selection
> algorithm.) What program is giving you the display right now? Is it a
> client, or a tracker on the web? I don't see the string "distributed"
> anywhere in Bram Cohen's 3.4.2 sources.

The wording of "distributed copies" was originally added by ChocoEd's
statistics patch (http://www.edkeyes.org/btstats.html) to Bram's
official client. The number of distributed copies is generally shown in
your client, and only counts the peers (usually not counting seeds)[0]
you are connected to.  I don't believe I've ever seen a tracker show the
distributed copies.

>    What I do observe is that the Knoppix BitTorrent site
> (http://torrent.unix-ag.uni-kl.de:6969/) displays average progress for
> its downloads. Average progress there is currently 29% on the english
> downloads, reporting 62 seeds and 12 "leechers" (who are downloading
> and uploading - because the tracker has no clue if a peer isn't
> uploading). Obviously if the seeds were included in this "average"
> then this number would have to be higher than 50%, so I think that
> this tracker averages across the peers that don't have the complete
> file yet. Is it possible that "distributed copies" means "average
> progress"?

Nope. Average copies (sometimes seend as XX.X% done/downloaded) is just
pretty much what you said. Add up the percentage complete of all the
peers, and divide by the number of peers. Going back to Samuel's 5 part
file example (slightly modified):

Alice 1 2 3 4
Bob   1   3 4
Carol   2 3
(nobody has piece 5)

Our average copies is (80% + 60% + 40%)/3 or 60%, but our distributed
copies is 0.80 (or 80%) because we can make 0.8 complete copies with
what is out there.

If Carol suddenly gets piece 5 (from some unknown seed) our average
copies goes to (80% + 60% + 60%)/3 or 66%, but your distributed copies
goes to 1.80 (Alice's 4 pieces and Carol's piece 5 make 1. Bob's 3 and
Carol's piece 2 make the .8. Carol's last piece is not counted.)

[0] Some clients will include seeds in this count, but will usually name
it something different, like "Available copies"