Re: Disk cache

> MooPolice@xxxxxxxxxxxxxx wrote:
> >>>Ah, I see... I had not thought of such a scenario. Very interesting.
> >>>
> >>>So, in a torrent like you described (1 seed, 1 hidden/offline peer, 1
> >>>blind peer), assuming downloaders get 1/2 of the file each, they would
> >>>be able to finish only if they have complementary halves of the file.
> >>>
> >>>With a randomization at the piece level, with say, 1,000 pieces in
> >>>total, each of the downloaders need the right 500 pieces to make the
> >>>torrent healthy.
> >>>
> >>>The probability for the blind client downloading the right 500 pieces,
> >>>not knowing which 500 the hidden peer has, are about 1/(2^1000), since
> >>>each piece has 1/2 chance of being the right piece, and that there are
> >>>1000 guesses to be made.
> >>>
> >>>I still think sequential downloading gives the torrent a better chance
> >>>for healing:
> >>>
> >>>Say that each client downloads quarters of the file in random  
> >>>order. The
> >>>pieces in each quarter are downloaded sequentially. (ie, all the  
> >>>pieces
> >>>in quarter 1 are downloaded in sequential order, but the file may be
> >>>downloaded as Q2,Q4,Q3,Q1)
> >>>
> >>>In this case, if the torrent behaves like you described above, the
> >>>chances for the torrent remaining healthy with the blind and hidden
> >>>peers present, but seed absent, are about 1/(2^4), since there are 4
> >>>guesses to be made. If each of the clients has 1/2 of the file when  
> >>>the
> >>>seed goes away, they have a 1/16 chance of finishing.
> >>>
> >>>So comparing a download strategy of piece-by-piece-randomly (PBPR) or
> >>>quarter-by-quarter-randomly (QBQR), the QBQR strategy has a 6.25%  
> >>>chance
> >>>of finishing, while PBPR has no (1/(2^1000)) chance of finishing.
> >>>
> >>>I think even the 6.25% probability can be improved:
> >>>
> >>>If the file is downloaded in halves instead, there is a 25% chance of
> >>>finishing this download. Perhaps each client can decide whether to
> >>>download halves, quarters, eights or whatever, depending on how many
> >>>peers it encounters:
> >>>
> >>>1 seed, 0 peers  = download halves
> >>>1 seed, 1 peer   = download quarters
> >>>2 seeds, 2 peers = download eights
> >>>
> >>>What do you think?
> >>
> > There is superseeding ... which defeats this appoarch totally.
> > 
> > MassaRoddel
> 
> What does superseeding have to do with improving lifespan of hard drives?
> 

You assume that you can see the seed and then make sequential downloads
but superseeding was made to prevent that. In that case you are forced by the
peer to download random pieces from the peer.


-------------------------------------------------------
Using Tomcat but need to do more? Need to support web services, security?
Get stuff done quickly with pre-integrated technology to make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642