Super-seeding is an algorithm developed by John Hoffman for the BitTorrent communications protocol.
The algorithm applies to a scenario in which there is only one seed in the swarm. By permitting each downloader to download only specific parts of the files listed in a torrent, it equips peers to begin seeding sooner.[1]
In 2003, BitTornado became the first BitTorrent client to implement the algorithm.
Algorithm
Rather than claiming to have every piece from the outset, the seeder claims to have no pieces. As peers connect, the seed will inform a peer that it has received a new piece, one that has not yet been sent to any other peers. The seed then unchokes the peer and allows it to download the piece. The seed will not upload another piece to the same peer until the seed receives confirmation from other peers that the piece has been uploaded again.
Effects
The intent of strictly limiting the uploading of duplicate pieces is that a super seeder will upload fewer bits than a standard seeder would before peers begin to complete, though it does not necessarily mean that the initial seed will complete in less time. Duration until the first completion of a downloader during a super seed is limited by the upload rate of the peers connected to the super seeder. Additionally, the seed does not have global information about piece distribution, and may not be informed of a piece being uploaded if the piece is uploaded to a peer not connected to the seed (which often occurs when the seed cannot accept incoming connections). If many seeds on a mature torrent are using super seed mode, the performance of the torrent will be limited.
Super seed mode is most useful for seeds that pay for upload bandwidth by the byte. In that case, super seeding makes sense as it minimizes the costs required to seed a torrent. Additionally, when one has a low upload speed super seed is very efficient. In other cases, the benefits of super seeding are not so clear. The configuration of peers and their individual upload capacities over the spectrum of individual torrents varies widely.
Testing by one group found that super seeding can help save an upload ratio of around 20%. It works best when the upload speed of the seed is greater than that of individual peers.[2]
The overall positive effect is not reserved only for the initial seeder, however, because the method creates multiple seeds in a more efficient manner than "average" seeding in a limited number of cases (one seeder, multiple incomplete peers). In theory, once the initial seeder uploads one complete copy of the file, multiple new seeds should emerge in a matter of minutes, thus boosting the overall uploading speed of the swarm. In practice, the results may vary for various reasons.
Super seeding transfers stall when there is only one downloading client. The seeders will not send more data until a second client receives the data. To avoid this, rTorrent continues to offer more pieces to the peers without waiting for confirmation, until it is uploading at its configured capacity.[3] This improves the upload speed until enough peers have joined the swarm, at the cost of not being able to detect cheating peers. Vuze uses an unknown method to prevent stalling,[citation needed] but it still limits upload speed[citation needed]. It is not known if any other implementations use a timeout or other solution. When uploading to a single client, it's recommended to disable super-seeding.
Supporting clients
References
External links
