[tahoe-dev] [tahoe-lafs] #778: "shares of happiness" is the wrong measure; "servers of happiness" is better

tahoe-lafs trac at allmydata.org
Tue Aug 18 19:20:29 UTC 2009


#778: "shares of happiness" is the wrong measure; "servers of happiness" is
better
--------------------------------+-------------------------------------------
 Reporter:  zooko               |           Owner:           
     Type:  defect              |          Status:  new      
 Priority:  critical            |       Milestone:  undecided
Component:  code-peerselection  |         Version:  1.4.1    
 Keywords:  reliability         |   Launchpad_bug:           
--------------------------------+-------------------------------------------

Comment(by davidsarah):

 > If {{{k_e / k}}} is not an integer, the minimal {{{m_e}}} is a little
 more complicated. In that case, most of the servers must have {{{1 + k_e
 // k}}} shares, but {{{k-1}}} of them only need {{{k_e // k shares}}}.
 > So {{{m_e = (n-k-1)*(1 + k_e // k) + (k-1)*(1 + k_e // k)}}}.
 Rearranging gives {{{m_e = n - k + 1 + n * (k_e // k)}}}.

 The first expression for {{{m_e}}} is wrong, even though the rest of the
 argument and the rearranged version is correct. What you mean is:

 ... So {{{m_e = (n-(k-1))*(1 + k_e // k) + (k-1)*(k_e // k)}}}.
 Rearranging gives {{{m_e = n - k + 1 + n * (k_e // k)}}}.

-- 
Ticket URL: <http://allmydata.org/trac/tahoe/ticket/778#comment:27>
tahoe-lafs <http://allmydata.org>
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