[tahoe-lafs-trac-stream] [tahoe-lafs] #2107: don't place shares on servers that already have shares

[tahoe-lafs]

#2107: don't place shares on servers that already have shares
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     Reporter:  zooko            |      Owner:
         Type:  enhancement      |     Status:  new
     Priority:  normal           |  Milestone:  undecided
    Component:  code-            |    Version:  1.10.0
  peerselection                  |   Keywords:  upload servers-of-happiness
   Resolution:                   |
Launchpad Bug:                   |
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Comment (by zooko):

 Replying to [comment:8 daira]:
 > Replying to [comment:7 zooko]:
 > > Well, no, that doesn't make sense ''either''. Because suppose you have
 K=3, N=6 and there are 6 servers. Well, putting a share on the first
 server will not increase the happiness level! It will be 0 both before and
 after placing that one share.
 >
 > No, it will be 1 after placing the share.
 >
 > It was intentional that the definition of happiness distinguishes
 between happiness levels less than K, even though none of them are
 sufficient for the file to be recoverable (this was an advantage of the
 maximum matching formulation over the "number of servers, the survival and
 correct function of which will guarantee that your file is available"
 definition that preceded it; see [ticket:778#comment:162]).

 Wait, what? I thought "Happiness" was defined as "The size of the largest
 set of servers such that any K-sized subset of it can recover your file".
 That number is 0 before and after uploading 1 share of a K=3 file. What
 ''is'' the definition of "Happiness"?

-- 
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2107#comment:9>
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