Implement error driven snowflake hardcoded with a single beta (#2978)

snow/consensus/snowball/binary_snowflake.go

@@ -11,29 +11,38 @@ func newBinarySnowflake(alphaPreference, alphaConfidence, beta, choice int) bina
 	return binarySnowflake{
 		binarySlush:     newBinarySlush(choice),
 		alphaPreference: alphaPreference,
-		alphaConfidence: alphaConfidence,
-		beta:            beta,
+		terminationConditions: []terminationCondition{
+			{
+				alphaConfidence: alphaConfidence,
+				beta:            beta,
+			},
+		},
+		confidence: make([]int, 1),
 	}
 }
 
 // binarySnowflake is the implementation of a binary snowflake instance
+// Invariant:
+// len(terminationConditions) == len(confidence)
+// terminationConditions[i].alphaConfidence < terminationConditions[i+1].alphaConfidence
+// terminationConditions[i].beta <= terminationConditions[i+1].beta
+// confidence[i] >= confidence[i+1] (except after finalizing due to early termination)
 type binarySnowflake struct {
 	// wrap the binary slush logic
 	binarySlush
 
-	// confidence tracks the number of successful polls in a row that have
-	// returned the preference
-	confidence int
-
 	// alphaPreference is the threshold required to update the preference
 	alphaPreference int
 
-	// alphaConfidence is the threshold required to increment the confidence counter
-	alphaConfidence int
+	// terminationConditions gives the ascending ordered list of alphaConfidence values
+	// required to increment the corresponding confidence counter.
+	// The corresponding beta values give the threshold required to finalize this instance.
+	terminationConditions []terminationCondition
 
-	// beta is the number of consecutive successful queries required for
-	// finalization.
-	beta int
+	// confidence is the number of consecutive succcessful polls for a given
+	// alphaConfidence threshold.
+	// This instance finalizes when confidence[i] >= terminationConditions[i].beta for any i
+	confidence []int
 
 	// finalized prevents the state from changing after the required number of
 	// consecutive polls has been reached
@@ -50,26 +59,34 @@ func (sf *binarySnowflake) RecordPoll(count, choice int) {
 		return
 	}
 
-	if count < sf.alphaConfidence {
-		sf.confidence = 0
-		sf.binarySlush.RecordSuccessfulPoll(choice)
-		return
+	// If I am changing my preference, reset confidence counters
+	// before recording a successful poll on the slush instance.
+	if choice != sf.Preference() {
+		clear(sf.confidence)
 	}
+	sf.binarySlush.RecordSuccessfulPoll(choice)
 
-	if preference := sf.Preference(); preference == choice {
-		sf.confidence++
-	} else {
-		// confidence is set to 1 because there has already been 1 successful
-		// poll, namely this poll.
-		sf.confidence = 1
+	for i, terminationCondition := range sf.terminationConditions {
+		// If I did not reach this alpha threshold, I did not
+		// reach any more alpha thresholds.
+		// Clear the remaining confidence counters.
+		if count < terminationCondition.alphaConfidence {
+			clear(sf.confidence[i:])
+			return
+		}
+
+		// I reached this alpha threshold, increment the confidence counter
+		// and check if I can finalize.
+		sf.confidence[i]++
+		if sf.confidence[i] >= terminationCondition.beta {
+			sf.finalized = true
+			return
+		}
 	}
-
-	sf.finalized = sf.confidence >= sf.beta
-	sf.binarySlush.RecordSuccessfulPoll(choice)
 }
 
 func (sf *binarySnowflake) RecordUnsuccessfulPoll() {
-	sf.confidence = 0
+	clear(sf.confidence)
 }
 
 func (sf *binarySnowflake) Finalized() bool {
@@ -78,7 +95,7 @@ func (sf *binarySnowflake) Finalized() bool {
 
 func (sf *binarySnowflake) String() string {
 	return fmt.Sprintf("SF(Confidence = %d, Finalized = %v, %s)",
-		sf.confidence,
+		sf.confidence[0],
 		sf.finalized,
 		&sf.binarySlush)
 }

snow/consensus/snowball/nnary_snowflake.go

@@ -15,30 +15,39 @@ func newNnarySnowflake(alphaPreference, alphaConfidence, beta int, choice ids.ID
 	return nnarySnowflake{
 		nnarySlush:      newNnarySlush(choice),
 		alphaPreference: alphaPreference,
-		alphaConfidence: alphaConfidence,
-		beta:            beta,
+		terminationConditions: []terminationCondition{
+			{
+				alphaConfidence: alphaConfidence,
+				beta:            beta,
+			},
+		},
+		confidence: make([]int, 1),
 	}
 }
 
 // nnarySnowflake is the implementation of a snowflake instance with an
 // unbounded number of choices
+// Invariant:
+// len(terminationConditions) == len(confidence)
+// terminationConditions[i].alphaConfidence < terminationConditions[i+1].alphaConfidence
+// terminationConditions[i].beta <= terminationConditions[i+1].beta
+// confidence[i] >= confidence[i+1] (except after finalizing due to early termination)
 type nnarySnowflake struct {
 	// wrap the n-nary slush logic
 	nnarySlush
 
-	// beta is the number of consecutive successful queries required for
-	// finalization.
-	beta int
-
 	// alphaPreference is the threshold required to update the preference
 	alphaPreference int
 
-	// alphaConfidence is the threshold required to increment the confidence counter
-	alphaConfidence int
+	// terminationConditions gives the ascending ordered list of alphaConfidence values
+	// required to increment the corresponding confidence counter.
+	// The corresponding beta values give the threshold required to finalize this instance.
+	terminationConditions []terminationCondition
 
-	// confidence tracks the number of successful polls in a row that have
-	// returned the preference
-	confidence int
+	// confidence is the number of consecutive succcessful polls for a given
+	// alphaConfidence threshold.
+	// This instance finalizes when confidence[i] >= terminationConditions[i].beta for any i
+	confidence []int
 
 	// finalized prevents the state from changing after the required number of
 	// consecutive polls has been reached
@@ -57,26 +66,34 @@ func (sf *nnarySnowflake) RecordPoll(count int, choice ids.ID) {
 		return
 	}
 
-	if count < sf.alphaConfidence {
-		sf.confidence = 0
-		sf.nnarySlush.RecordSuccessfulPoll(choice)
-		return
+	// If I am changing my preference, reset confidence counters
+	// before recording a successful poll on the slush instance.
+	if choice != sf.Preference() {
+		clear(sf.confidence)
 	}
+	sf.nnarySlush.RecordSuccessfulPoll(choice)
 
-	if preference := sf.Preference(); preference == choice {
-		sf.confidence++
-	} else {
-		// confidence is set to 1 because there has already been 1 successful
-		// poll, namely this poll.
-		sf.confidence = 1
+	for i, terminationCondition := range sf.terminationConditions {
+		// If I did not reach this alpha threshold, I did not
+		// reach any more alpha thresholds.
+		// Clear the remaining confidence counters.
+		if count < terminationCondition.alphaConfidence {
+			clear(sf.confidence[i:])
+			return
+		}
+
+		// I reached this alpha threshold, increment the confidence counter
+		// and check if I can finalize.
+		sf.confidence[i]++
+		if sf.confidence[i] >= terminationCondition.beta {
+			sf.finalized = true
+			return
+		}
 	}
-
-	sf.finalized = sf.confidence >= sf.beta
-	sf.nnarySlush.RecordSuccessfulPoll(choice)
 }
 
 func (sf *nnarySnowflake) RecordUnsuccessfulPoll() {
-	sf.confidence = 0
+	clear(sf.confidence)
 }
 
 func (sf *nnarySnowflake) Finalized() bool {
@@ -85,7 +102,7 @@ func (sf *nnarySnowflake) Finalized() bool {
 
 func (sf *nnarySnowflake) String() string {
 	return fmt.Sprintf("SF(Confidence = %d, Finalized = %v, %s)",
-		sf.confidence,
+		sf.confidence[0],
 		sf.finalized,
 		&sf.nnarySlush)
 }

snow/consensus/snowball/parameters.go

@@ -122,3 +122,8 @@ func (p Parameters) MinPercentConnectedHealthy() float64 {
 	alphaRatio := float64(p.AlphaConfidence) / float64(p.K)
 	return alphaRatio*(1-MinPercentConnectedBuffer) + MinPercentConnectedBuffer
 }
+
+type terminationCondition struct {
+	alphaConfidence int
+	beta            int
+}

snow/consensus/snowball/unary_snowball.go

@@ -3,7 +3,10 @@
 
 package snowball
 
-import "fmt"
+import (
+	"fmt"
+	"slices"
+)
 
 var _ Unary = (*unarySnowball)(nil)
 
@@ -32,12 +35,11 @@ func (sb *unarySnowball) RecordPoll(count int) {
 func (sb *unarySnowball) Extend(choice int) Binary {
 	bs := &binarySnowball{
 		binarySnowflake: binarySnowflake{
-			binarySlush:     binarySlush{preference: choice},
-			confidence:      sb.confidence,
-			alphaPreference: sb.alphaPreference,
-			alphaConfidence: sb.alphaConfidence,
-			beta:            sb.beta,
-			finalized:       sb.Finalized(),
+			binarySlush:           binarySlush{preference: choice},
+			confidence:            slices.Clone(sb.confidence),
+			alphaPreference:       sb.alphaPreference,
+			terminationConditions: sb.terminationConditions,
+			finalized:             sb.Finalized(),
 		},
 		preference: choice,
 	}
@@ -47,6 +49,7 @@ func (sb *unarySnowball) Extend(choice int) Binary {
 
 func (sb *unarySnowball) Clone() Unary {
 	newSnowball := *sb
+	newSnowball.confidence = slices.Clone(sb.confidence)
 	return &newSnowball
 }
 

snow/consensus/snowball/unary_snowball_test.go

@@ -9,7 +9,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func UnarySnowballStateTest(t *testing.T, sb *unarySnowball, expectedPreferenceStrength, expectedConfidence int, expectedFinalized bool) {
+func UnarySnowballStateTest(t *testing.T, sb *unarySnowball, expectedPreferenceStrength int, expectedConfidence []int, expectedFinalized bool) {
 	require := require.New(t)
 
 	require.Equal(expectedPreferenceStrength, sb.preferenceStrength)
@@ -26,25 +26,25 @@ func TestUnarySnowball(t *testing.T) {
 	sb := newUnarySnowball(alphaPreference, alphaConfidence, beta)
 
 	sb.RecordPoll(alphaConfidence)
-	UnarySnowballStateTest(t, &sb, 1, 1, false)
+	UnarySnowballStateTest(t, &sb, 1, []int{1}, false)
 
 	sb.RecordPoll(alphaPreference)
-	UnarySnowballStateTest(t, &sb, 2, 0, false)
+	UnarySnowballStateTest(t, &sb, 2, []int{0}, false)
 
 	sb.RecordPoll(alphaConfidence)
-	UnarySnowballStateTest(t, &sb, 3, 1, false)
+	UnarySnowballStateTest(t, &sb, 3, []int{1}, false)
 
 	sb.RecordUnsuccessfulPoll()
-	UnarySnowballStateTest(t, &sb, 3, 0, false)
+	UnarySnowballStateTest(t, &sb, 3, []int{0}, false)
 
 	sb.RecordPoll(alphaConfidence)
-	UnarySnowballStateTest(t, &sb, 4, 1, false)
+	UnarySnowballStateTest(t, &sb, 4, []int{1}, false)
 
 	sbCloneIntf := sb.Clone()
 	require.IsType(&unarySnowball{}, sbCloneIntf)
 	sbClone := sbCloneIntf.(*unarySnowball)
 
-	UnarySnowballStateTest(t, sbClone, 4, 1, false)
+	UnarySnowballStateTest(t, sbClone, 4, []int{1}, false)
 
 	binarySnowball := sbClone.Extend(0)