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Explain Q and F #803

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Jan 13, 2020
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Explain Q and F #803

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Explain Q and F
Jan 9, 2020
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Merge branch 'master' into timmoreton/quorum-explain
Jan 10, 2020
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21 changes: 21 additions & 0 deletions consensus/istanbul/validator/default.go
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Expand Up @@ -247,6 +247,27 @@ func (valSet *defaultSet) Copy() istanbul.ValidatorSet {
return newValSet
}

// We include the optimization described at https://arxiv.org/pdf/1901.07160.pdf as “PM-6” and
// discussed in Lemma 22. For values of N=3F for integer F=1,2,3,.. we can tolerate a quorum
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// size one smaller than anticipated by Q = N - F. The intersection of any two sets of Q
// nodes of N=3F must contain an honest validator.
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//
// For example, with N=9, F=2, Q=6. Any two sets of Q=6 from N=9 nodes must overlap
// by >9-6=3 nodes. At least 3-F=3-2=1 must be honest.
//
// 1 2 3 4 5 6 7 8 9
// x x x x x x
// y y y y y y
// F F H
//
// For N=10, F=3, Q=7. Any two sets of Q=7 nodes from N=10 must overlap by >4 nodes.
// At least 4-F=4-3=1 must be honest.
//
// 1 2 3 4 5 6 7 8 9 10
// x x x x x x x
// y y y y y y y
// F F F H

func (valSet *defaultSet) F() int { return int(math.Ceil(float64(valSet.Size())/3)) - 1 }

func (valSet *defaultSet) MinQuorumSize() int {
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