The Local Hostcache

From Gnutella Developers

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In order to help the bootstrap process (see 2.1 Bootstrapping), a servent SHOULD implement a hosts cache (also sometimes called a hosts list), keeping a few hundreds hosts on the disc. The probability that at least one of them is running is very high, even when the list is several weeks old.

The hosts list has two purposes :

  1. Make connection times to the GNet shorter
  2. Make as less GWebCache calls per session as possible (ideally, only one).

The list of hosts is loaded when the servent is launched. It is filled with hosts grabbed from GWebCache calls, from X-Try and X-Try-Ultrapeer headers, from pongs, and optionally from queryHits. And it is saved (the whole list, or just a subset) when the user exits the application. A starting hosts list SHOULD be distributed with the client, filled with known servents having a regular activity on the GNet, so that even the very first time the servent is launched, it will be able to use the host cache. The list of hosts SHOULD NOT be hard coded, notably to avoid sending too many connections requests to the same small subset of the GNet.

Many enhancements to this scheme are possible. There are a lot of possibilities with keeping a big hosts list in RAM, but saving only a subset of it, based on some evaluation function. Hence, a client could store only hosts with which a "strong" GNet connection has been made, a connection being marked as strong after a few tenths of seconds, for instance one minute. A true evaluation function can also be computed, based on various parameters :

  • remote servent uptime.
  • remote servent shared files size and count
  • last time the remote servent was seen
  • whether a connection has been made with it
  • max uptime if a Gnet connection has been made.

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