[bittorrent] IO bound

Alan McGovern alan.mcgovern at gmail.com
Fri Apr 13 09:29:43 EDT 2007

> KTorrent ignores suggest piece messages. I have not found much use for
> them. Didn't feel like rewriting my chunk selection algorithm just so I can
> take into account these suggestions.

I would argue that you can't claim to support the fast extensions if you
ignore completely certain portions of the extension ;) To claim support you
should at least process any messages you receive, whatever about sending
them out yourself. What if 1/2 the implementers of the fast extensions
decided that they weren't going to support the FastPiece message because
they didn't want to rewrite their chunk selection algorithm? That would mean
that the faster bootstrapping into the swarm offered by this extension would
be gone!

While you may not have a use for SuggestPiece messages, other clients do.
Super-seeding (initial seeding) can be handled *much* more cleaning with the
introduction of the SuggestPiece message. You no longer have to resort to
hacks like lieing about your bitfield and selective HaveMessage sending. Of
course, if every client ignored SuggestPiece messages, any super-seeding
logic based on SuggestPiece messages would fail miserably, despite it being
better than the existing method.

Sending fake bitfields is a messy solution. It was necessary *before* the
SuggestPiece message was designed. In fact, i'd go as far to say as this is
the exact situation that the SuggestPiece message was designed to combat!

If every client obeyed the SuggestPiece message, you'd be *easily* able to
control what pieces are being requested and saturate your bandwidth. You
could load 10 pieces into memory, then send a SuggestPiece for each of those
pieces to a different group of peers (possibly each group being 10 peers in
size) meaning that each of your pieces would then be downloaded by 10 peers.
Once thats done, you could load a different 10 pieces into memory and
repeat. Thats roughly the kind of logic i'm planning on implementing, but
that won't happen for a few weeks ;)
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