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Clients that fetch torrents sequentially from the start - happening!


BlindFreddie

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A seed's goal is to keep availability of the torrent parts high, but if peers refuse to download the rare pieces first a seed's entire upload speed can be "spent" uploading parts multiple other peers already have. This is especially common for first+last pieces of files due to BitComet demanding those first and uTorrent/BitTorrent can be set to demand those pieces with a much higher priority. So a seed that's set to stop at a fixed ratio may stop before every piece of the torrent is uploaded to the peers.

I've also heard about seeds stopping in disgust after seeding 4-10:1 and not seeing any other seeds on the torrent. We get posts occasionally where people want to ban the peers that don't share, but refuse to add anything like that because many times the peers that don't share simply don't have any pieces that other peers don't already have. With firewalled and bad ISP peers/seeds mixed in, many peers and seeds cannot upload to all the peers on the torrent. Ideally, peers should download different pieces than each other, or the entire demand can fall on the (few?) seeds...and even BitTorrent's whole concept can fail. :(

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  • 4 weeks later...

I felt that transmission got a bad rap at the beginning of this thread, because it appeared to engage in sequential downloading. However, if you read the link, it's clear that transmission has rules that keep a swarm healthy (especially fetching the rarest piece first) and it only falls back on sequential downloading if there's just one seed and one leech - because in this case, it doesn't matter in what order the pieces are fetched. The examples given to show why sequential downloading kills swarms all use more than two participants... but in this case transmission does not do that!

In fact, because of the rule to fetch the rarest pieces first, in a swarm that contains bad clients (who are sequentially downloading on purpose) transmission will compensate for this bad behaviour by preferring later pieces (because they become rarer).

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  • 3 weeks later...

what i never understood is why people use full sequential downloading when setting high and low priority works just as well but at the same time allows all the files to be active. so to be honest instead of condemning sequential downloading why not campaign and try to educate users on how to properly assign priority to a file.

the do not download feature has one and only one purpose. and that is to block the downloading of suspicious files that could damage your computer like no cd cracks and key gens which people like to cram into their iso torrents even though most people who are looking for disk images already own the software and just need a replacement disk. but regardless they often contain viruses and thats what i use do not download for.

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  • 3 weeks later...

> why people use full sequential downloading

People want to watch video before the file is complete. VLC can stream an incomplete file as long as the file sections VLC streams are physically on the hard drive. I have unRARed AVI files and started watching the AVI while the AVI file was being assembled.

While sequential piece requests (with hit-n-run) does affect availability, I'd like to see a technological solution to address this behavior. Once Project Pheon is complete, users may prefer to use that technology to watch video instead of bittorrent. We'll see.

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  • 1 year later...

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