Tracker scrape

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A scrape, or tracker scrape, is a request sent by a BitTorrent client to a tracker. A request is sent, connection to the tracker is established, information is exchanged, then the connection is closed. The request does something like a "wipe" or a "pass" over the tracker, and then the tracker sends information back to the client. [1] [2]

A BitTorrent tracker is a special type of server that assists in the communication between peers using the BitTorrent protocol. In peer-to-peer file sharing, a software client on an end-user PC requests a file, and portions of the requested file residing on peer machines are sent to the client, and then reassembled into a full copy of the requested file. The "tracker" server keeps track of where file copies reside on peer machines, which ones are available at time of the client request, and helps coordinate efficient transmission and reassembly of the copied file. Clients that have already begun downloading a file communicate with the tracker periodically to negotiate faster file transfer with new peers, and provide network performance statistics; however, after the initial peer-to-peer file download is started, peer-to-peer communication can continue without the connection to a tracker. Since the creation of the distributed hash table (DHT) method for "Trackerless" torrents, BitTorrent trackers have largely become redundant; however, they are still often included with torrents to improve the speed of peer discovery.

The returned information can contain such information as, whether the tracker is on- or offline, the reason it is offline, the numbers of peers and seeds (sending a list of all peers in the swarm is usually much more bandwidth consuming than just sending a scrape result), etc. Note that some trackers don't support scrape requests, but it is still possible to use the tracker as usual.

A client scrapes in order to determine whether or not to send an announce requesting more peers. Sending a scrape result usually requires less data transfer than sending a list of peers.

Clients with scrape support will scrape the tracker many times during the course of a download to update its information about the swarm. The tracker is scraped many thousands of times for each torrent alone, even if the swarm is not very big. The tracker can usually handle this number of requests. However, if there are more requests than strictly necessary, this can destabilize the tracker and put it offline.

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References

  1. ↑ "Vuze Wiki: Scrape". Vuze. 2012-01-12. Retrieved 2018-07-27.
  2. ↑ "Bittorrent Protocol Specification v1.0: Tracker 'scrape' Convention". 2017-02-01. Retrieved 2018-07-27.
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