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

[Ken Bloom]

On Mon, Jul 26, 2004 at 02:46:48PM -0700, Peter Jay Salzman wrote:
> On Mon 26 Jul 04,  2:37 PM, Samuel N. Merritt <spam at andcheese.org> said:
> > On Mon, Jul 26, 2004 at 02:08:22PM -0700, Peter Jay Salzman wrote:
> > > Question:
> > > 
> > > How does the "distributed copies" get larger when there are no seeds?
> > 
> > I think that "distributed copies" measures how many complete copies of
> > the file you could get if you took all the pieces that everyone has and
> > assembled them. 
> > 
> > For example, consider a five-part file.
> > Alice has: 1 2 3 4
> > Bob has:       3 4 5 
> > Carol has: 1 2   4 
> > 
> > You could make one complete copy of the file from all this, so there'd
> > be 1 distributed copy. If Carol got piece 5 from Bob, then you could
> > assemble two complete copies. 
> > 
> > That's the integer part of distributed copies; I'm not sure where the
> > fractional part comes from. Maybe it's the size of the largest
> > distributed incomplete subfile divided by size of file, but that's just
> > a shot in the dark. 
>   
> ok.  this was my understanding.
> 
> > > Does the tracker ever inject packets into the torrent when needed (like
> > > when seeds == 0 and distributed copies < 1.0)?
> > 
> > No. The tracker doesn't have a local copy of the file. If there are no
> > seeds and < 1 distributed copy, everyone's download will stall before
> > finishing 
> 
> this was also my understanding.  but my question still stands: how does
> the distributed copies increase if there are no seeds?
> 
> i'm looking at a bittorrent right now.  it's remained constant at:
> 
>    seeds: 0 seen now, plus 0.983 distributed copies
>    peers: 19 seen now, 98.4% done at 0.2 kB/s
> 
> that ".983 distributed copies" has been creeping upwards.  last i looked
> at it, about 15 minutes ago, it was at .97.   i've noticed this happen
> before too.
> 
> how exactly does that number increase when there are no seeds?

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.

   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"?

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