[bittorrent] Friend-machines-assisted approach to boosting one's BT download

Elliott Mitchell ehem at m5p.com
Sun Jun 11 13:54:54 EDT 2006

>From: Harold Feit <dwknight at depthstrike.com>
> As on-topic as this suggestion may be, it has not been met with the best
> of responses in the development community.
> By having friend systems not duplicate pieces within the friend cluster
> until after 1.0 distribution within the cluster, the cluster is causing
> an overall negative skew of the distribution of pieces within the swarm
> as a whole, causing degradation in swarm-wide performance.

State the reasoning.

I don't see how this would happen. If you were calculating your numbers
incorrectly, I can easily see how you would come to this conclusion, but
this doesn't match reality. In particular if you count each member of the
group as a true distinct peer, then yes you reach this conclusion. Since
there is only one true downloader here though, you must count the entire
aggregate _group_ as one peer.

If the central system advertises possession of pieces it got from
slaves, then you will see all pieces that the helpers download advertised
from two semi-distinct peers. All pieces the central system downloads
from the swam will only be advertised once. This though should not have a
major impact on the balance of the swarm (self-interest on the part of
normal peers should easily even this out), though it is a decent reason
to forbid the central system from advertising possession of pieces it
gets from slaves.

> Additionally, having the friend cluster separate itself from the main
> swarm once it has reached 1.0 distribution within the cluster causes
> even MORE of a negative skew of piece distribution of pieces within the
> swarm.
> It could potentially make one downloading user faster, at the cost of
> everyone else in the swarm.

This is the old "don't disconnect immediately" request. Your slaves
should only disconnect when the master shuts down.

And how do you prevent the implementation of this anyway? This is trivial
compared any of the other attacks on the swarm that come to mind. Come up
with defenses, don't ignore something that can be done.

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