treat validator updates as set (#3222)

* Initial commit for 3181..still early

* unit test updates

* unit test updates

* fix check of dups accross updates and deletes

* simplify the processChange() func

* added overflow check utest

* Added checks for empty valset, new utest

* deepcopy changes in processUpdate()

* moved to new API, fixed tests

* test cleanup

* address review comments

* make sure votePower > 0

* gofmt fixes

* handle duplicates and invalid values

* more work on tests, review comments

* Renamed and explained K

* make TestVal private

* split verifyUpdatesAndComputeNewPriorities.., added check for deletes

* return error if validator set is empty after processing changes

* address review comments

* lint err

* Fixed the total voting power and added comments

* fix lint

* fix lint

state/execution.go

@@ -2,7 +2,6 @@ package state
 
 import (
 	"fmt"
-	"strings"
 	"time"
 
 	abci "github.com/tendermint/tendermint/abci/types"
@@ -143,7 +142,7 @@ func (blockExec *BlockExecutor) ApplyBlock(state State, blockID types.BlockID, b
 		return state, err
 	}
 	if len(validatorUpdates) > 0 {
-		blockExec.logger.Info("Updates to validators", "updates", makeValidatorUpdatesLogString(validatorUpdates))
+		blockExec.logger.Info("Updates to validators", "updates", types.ValidatorListString(validatorUpdates))
 	}
 
 	// Update the state with the block and responses.
@@ -368,70 +367,6 @@ func validateValidatorUpdates(abciUpdates []abci.ValidatorUpdate,
 	return nil
 }
 
-// If more or equal than 1/3 of total voting power changed in one block, then
-// a light client could never prove the transition externally. See
-// ./lite/doc.go for details on how a light client tracks validators.
-func updateValidators(currentSet *types.ValidatorSet, updates []*types.Validator) error {
-	for _, valUpdate := range updates {
-		// should already have been checked
-		if valUpdate.VotingPower < 0 {
-			return fmt.Errorf("Voting power can't be negative %v", valUpdate)
-		}
-
-		address := valUpdate.Address
-		_, val := currentSet.GetByAddress(address)
-		// valUpdate.VotingPower is ensured to be non-negative in validation method
-		if valUpdate.VotingPower == 0 { // remove val
-			_, removed := currentSet.Remove(address)
-			if !removed {
-				return fmt.Errorf("Failed to remove validator %X", address)
-			}
-		} else if val == nil { // add val
-			// make sure we do not exceed MaxTotalVotingPower by adding this validator:
-			totalVotingPower := currentSet.TotalVotingPower()
-			updatedVotingPower := valUpdate.VotingPower + totalVotingPower
-			overflow := updatedVotingPower > types.MaxTotalVotingPower || updatedVotingPower < 0
-			if overflow {
-				return fmt.Errorf(
-					"Failed to add new validator %v. Adding it would exceed max allowed total voting power %v",
-					valUpdate,
-					types.MaxTotalVotingPower)
-			}
-			// TODO: issue #1558 update spec according to the following:
-			// Set ProposerPriority to -C*totalVotingPower (with C ~= 1.125) to make sure validators can't
-			// unbond/rebond to reset their (potentially previously negative) ProposerPriority to zero.
-			//
-			// Contract: totalVotingPower < MaxTotalVotingPower to ensure ProposerPriority does
-			// not exceed the bounds of int64.
-			//
-			// Compute ProposerPriority = -1.125*totalVotingPower == -(totalVotingPower + (totalVotingPower >> 3)).
-			valUpdate.ProposerPriority = -(totalVotingPower + (totalVotingPower >> 3))
-			added := currentSet.Add(valUpdate)
-			if !added {
-				return fmt.Errorf("Failed to add new validator %v", valUpdate)
-			}
-		} else { // update val
-			// make sure we do not exceed MaxTotalVotingPower by updating this validator:
-			totalVotingPower := currentSet.TotalVotingPower()
-			curVotingPower := val.VotingPower
-			updatedVotingPower := totalVotingPower - curVotingPower + valUpdate.VotingPower
-			overflow := updatedVotingPower > types.MaxTotalVotingPower || updatedVotingPower < 0
-			if overflow {
-				return fmt.Errorf(
-					"Failed to update existing validator %v. Updating it would exceed max allowed total voting power %v",
-					valUpdate,
-					types.MaxTotalVotingPower)
-			}
-
-			updated := currentSet.Update(valUpdate)
-			if !updated {
-				return fmt.Errorf("Failed to update validator %X to %v", address, valUpdate)
-			}
-		}
-	}
-	return nil
-}
-
 // updateState returns a new State updated according to the header and responses.
 func updateState(
 	state State,
@@ -448,7 +383,7 @@ func updateState(
 	// Update the validator set with the latest abciResponses.
 	lastHeightValsChanged := state.LastHeightValidatorsChanged
 	if len(validatorUpdates) > 0 {
-		err := updateValidators(nValSet, validatorUpdates)
+		err := nValSet.UpdateWithChangeSet(validatorUpdates)
 		if err != nil {
 			return state, fmt.Errorf("Error changing validator set: %v", err)
 		}
@@ -552,13 +487,3 @@ func ExecCommitBlock(
 	// ResponseCommit has no error or log, just data
 	return res.Data, nil
 }
-
-// Make pretty string for validatorUpdates logging
-func makeValidatorUpdatesLogString(vals []*types.Validator) string {
-	chunks := make([]string, len(vals))
-	for i, val := range vals {
-		chunks[i] = fmt.Sprintf("%s:%d", val.Address, val.VotingPower)
-	}
-
-	return strings.Join(chunks, ",")
-}

state/execution_test.go

@@ -280,7 +280,7 @@ func TestUpdateValidators(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			updates, err := types.PB2TM.ValidatorUpdates(tc.abciUpdates)
 			assert.NoError(t, err)
-			err = updateValidators(tc.currentSet, updates)
+			err = tc.currentSet.UpdateWithChangeSet(updates)
 			if tc.shouldErr {
 				assert.Error(t, err)
 			} else {

state/state_test.go

@@ -322,7 +322,8 @@ func TestProposerFrequency(t *testing.T) {
 		vals := make([]*types.Validator, N)
 		totalVotePower := int64(0)
 		for j := 0; j < N; j++ {
-			votePower := int64(cmn.RandInt() % maxPower)
+			// make sure votePower > 0
+			votePower := int64(cmn.RandInt()%maxPower) + 1
 			totalVotePower += votePower
 			privVal := types.NewMockPV()
 			pubKey := privVal.GetPubKey()
@@ -424,49 +425,71 @@ func TestProposerPriorityDoesNotGetResetToZero(t *testing.T) {
 	require.Equal(t, len(updatedState2.NextValidators.Validators), 2)
 	_, updatedVal1 := updatedState2.NextValidators.GetByAddress(val1PubKey.Address())
 	_, addedVal2 := updatedState2.NextValidators.GetByAddress(val2PubKey.Address())
+
 	// adding a validator should not lead to a ProposerPriority equal to zero (unless the combination of averaging and
 	// incrementing would cause so; which is not the case here)
-	totalPowerBefore2 := curTotal
-	// while adding we compute prio == -1.125 * total:
-	wantVal2ProposerPrio := -(totalPowerBefore2 + (totalPowerBefore2 >> 3))
-	wantVal2ProposerPrio = wantVal2ProposerPrio + val2VotingPower
-	// then increment:
+	// Steps from adding new validator:
+	// 0 - val1 prio is 0, TVP after add:
+	wantVal1Prio := int64(0)
 	totalPowerAfter := val1VotingPower + val2VotingPower
-	// mostest:
-	wantVal2ProposerPrio = wantVal2ProposerPrio - totalPowerAfter
-	avg := big.NewInt(0).Add(big.NewInt(val1VotingPower), big.NewInt(wantVal2ProposerPrio))
+	// 1. Add - Val2 should be initially added with (-123) =>
+	wantVal2Prio := -(totalPowerAfter + (totalPowerAfter >> 3))
+	// 2. Scale - noop
+	// 3. Center - with avg, resulting val2:-61, val1:62
+	avg := big.NewInt(0).Add(big.NewInt(wantVal1Prio), big.NewInt(wantVal2Prio))
 	avg.Div(avg, big.NewInt(2))
-	wantVal2ProposerPrio = wantVal2ProposerPrio - avg.Int64()
-	wantVal1Prio := 0 + val1VotingPower - avg.Int64()
+	wantVal2Prio = wantVal2Prio - avg.Int64() // -61
+	wantVal1Prio = wantVal1Prio - avg.Int64() // 62
+
+	// 4. Steps from IncrementProposerPriority
+	wantVal1Prio = wantVal1Prio + val1VotingPower // 72
+	wantVal2Prio = wantVal2Prio + val2VotingPower // 39
+	wantVal1Prio = wantVal1Prio - totalPowerAfter // -38 as val1 is proposer
+
 	assert.Equal(t, wantVal1Prio, updatedVal1.ProposerPriority)
-	assert.Equal(t, wantVal2ProposerPrio, addedVal2.ProposerPriority)
+	assert.Equal(t, wantVal2Prio, addedVal2.ProposerPriority)
 
 	// Updating a validator does not reset the ProposerPriority to zero:
+	// 1. Add - Val2 VotingPower change to 1 =>
 	updatedVotingPowVal2 := int64(1)
 	updateVal := abci.ValidatorUpdate{PubKey: types.TM2PB.PubKey(val2PubKey), Power: updatedVotingPowVal2}
 	validatorUpdates, err = types.PB2TM.ValidatorUpdates([]abci.ValidatorUpdate{updateVal})
 	assert.NoError(t, err)
 
-	// this will cause the diff of priorities (31)
+	// this will cause the diff of priorities (77)
 	// to be larger than threshold == 2*totalVotingPower (22):
 	updatedState3, err := updateState(updatedState2, blockID, &block.Header, abciResponses, validatorUpdates)
 	assert.NoError(t, err)
 
 	require.Equal(t, len(updatedState3.NextValidators.Validators), 2)
 	_, prevVal1 := updatedState3.Validators.GetByAddress(val1PubKey.Address())
+	_, prevVal2 := updatedState3.Validators.GetByAddress(val2PubKey.Address())
+	_, updatedVal1 = updatedState3.NextValidators.GetByAddress(val1PubKey.Address())
 	_, updatedVal2 := updatedState3.NextValidators.GetByAddress(val2PubKey.Address())
 
-	// divide previous priorities by 2 == CEIL(31/22) as diff > threshold:
-	expectedVal1PrioBeforeAvg := prevVal1.ProposerPriority/2 + prevVal1.VotingPower
-	wantVal2ProposerPrio = wantVal2ProposerPrio/2 + updatedVotingPowVal2
-	// val1 will be proposer:
-	total := val1VotingPower + updatedVotingPowVal2
-	expectedVal1PrioBeforeAvg = expectedVal1PrioBeforeAvg - total
-	avgI64 := (wantVal2ProposerPrio + expectedVal1PrioBeforeAvg) / 2
-	wantVal2ProposerPrio = wantVal2ProposerPrio - avgI64
-	wantVal1Prio = expectedVal1PrioBeforeAvg - avgI64
-	assert.Equal(t, wantVal2ProposerPrio, updatedVal2.ProposerPriority)
-	_, updatedVal1 = updatedState3.NextValidators.GetByAddress(val1PubKey.Address())
+	// 2. Scale
+	// old prios: v1(10):-38, v2(1):39
+	wantVal1Prio = prevVal1.ProposerPriority
+	wantVal2Prio = prevVal2.ProposerPriority
+	// scale to diffMax = 22 = 2 * tvp, diff=39-(-38)=77
+	// new totalPower
+	totalPower := updatedVal1.VotingPower + updatedVal2.VotingPower
+	dist := wantVal2Prio - wantVal1Prio
+	// ratio := (dist + 2*totalPower - 1) / 2*totalPower = 98/22 = 4
+	ratio := (dist + 2*totalPower - 1) / (2 * totalPower)
+	// v1(10):-38/4, v2(1):39/4
+	wantVal1Prio /= ratio // -9
+	wantVal2Prio /= ratio // 9
+
+	// 3. Center - noop
+	// 4. IncrementProposerPriority() ->
+	// v1(10):-9+10, v2(1):9+1 -> v2 proposer so subsract tvp(11)
+	// v1(10):1, v2(1):-1
+	wantVal2Prio += updatedVal2.VotingPower // 10 -> prop
+	wantVal1Prio += updatedVal1.VotingPower // 1
+	wantVal2Prio -= totalPower              // -1
+
+	assert.Equal(t, wantVal2Prio, updatedVal2.ProposerPriority)
 	assert.Equal(t, wantVal1Prio, updatedVal1.ProposerPriority)
 }
 
@@ -527,22 +550,22 @@ func TestProposerPriorityProposerAlternates(t *testing.T) {
 	_, oldVal1 := updatedState2.Validators.GetByAddress(val1PubKey.Address())
 	_, updatedVal2 := updatedState2.NextValidators.GetByAddress(val2PubKey.Address())
 
-	totalPower = val1VotingPower // no update
-	v2PrioWhenAddedVal2 := -(totalPower + (totalPower >> 3))
-	v2PrioWhenAddedVal2 = v2PrioWhenAddedVal2 + val1VotingPower       // -11 + 10 == -1
-	v1PrioWhenAddedVal2 := oldVal1.ProposerPriority + val1VotingPower // -10 + 10 == 0
-	totalPower = 2 * val1VotingPower                                  // now we have to validators with that power
-	v1PrioWhenAddedVal2 = v1PrioWhenAddedVal2 - totalPower            // mostest
-	// have to express the AVG in big.Ints as -1/2 == -1 in big.Int while -1/2 == 0 in int64
-	avgSum := big.NewInt(0).Add(big.NewInt(v2PrioWhenAddedVal2), big.NewInt(v1PrioWhenAddedVal2))
-	avg := avgSum.Div(avgSum, big.NewInt(2))
-	expectedVal2Prio := v2PrioWhenAddedVal2 - avg.Int64()
-	totalPower = 2 * val1VotingPower // 10 + 10
-	expectedVal1Prio := oldVal1.ProposerPriority + val1VotingPower - avg.Int64() - totalPower
-	// val1's ProposerPriority story: -10 (see above) + 10 (voting pow) - (-1) (avg) - 20 (total) == -19
+	// 1. Add
+	val2VotingPower := val1VotingPower
+	totalPower = val1VotingPower + val2VotingPower           // 20
+	v2PrioWhenAddedVal2 := -(totalPower + (totalPower >> 3)) // -22
+	// 2. Scale - noop
+	// 3. Center
+	avgSum := big.NewInt(0).Add(big.NewInt(v2PrioWhenAddedVal2), big.NewInt(oldVal1.ProposerPriority))
+	avg := avgSum.Div(avgSum, big.NewInt(2))                   // -11
+	expectedVal2Prio := v2PrioWhenAddedVal2 - avg.Int64()      // -11
+	expectedVal1Prio := oldVal1.ProposerPriority - avg.Int64() // 11
+	// 4. Increment
+	expectedVal2Prio = expectedVal2Prio + val2VotingPower // -11 + 10 = -1
+	expectedVal1Prio = expectedVal1Prio + val1VotingPower // 11 + 10 == 21
+	expectedVal1Prio = expectedVal1Prio - totalPower      // 1, val1 proposer
+
 	assert.EqualValues(t, expectedVal1Prio, updatedVal1.ProposerPriority)
-	// val2 prio when added: -(totalVotingPower + (totalVotingPower >> 3)) == -11
-	// -> -11 + 10  (voting power) - (-1) (avg) == 0
 	assert.EqualValues(t, expectedVal2Prio, updatedVal2.ProposerPriority, "unexpected proposer priority for validator: %v", updatedVal2)
 
 	validatorUpdates, err = types.PB2TM.ValidatorUpdates(abciResponses.EndBlock.ValidatorUpdates)
@@ -551,34 +574,40 @@ func TestProposerPriorityProposerAlternates(t *testing.T) {
 	updatedState3, err := updateState(updatedState2, blockID, &block.Header, abciResponses, validatorUpdates)
 	assert.NoError(t, err)
 
-	// proposer changes from now on (every iteration) as long as there are no changes in the validator set:
-	assert.NotEqual(t, updatedState3.Validators.Proposer.Address, updatedState3.NextValidators.Proposer.Address)
+	assert.Equal(t, updatedState3.Validators.Proposer.Address, updatedState3.NextValidators.Proposer.Address)
 
 	assert.Equal(t, updatedState3.Validators, updatedState2.NextValidators)
 	_, updatedVal1 = updatedState3.NextValidators.GetByAddress(val1PubKey.Address())
-	_, oldVal1 = updatedState3.Validators.GetByAddress(val1PubKey.Address())
 	_, updatedVal2 = updatedState3.NextValidators.GetByAddress(val2PubKey.Address())
-	_, oldVal2 := updatedState3.Validators.GetByAddress(val2PubKey.Address())
 
-	// val2 will be proposer:
-	assert.Equal(t, val2PubKey.Address(), updatedState3.NextValidators.Proposer.Address)
-	// check if expected proposer prio is matched:
+	// val1 will still be proposer:
+	assert.Equal(t, val1PubKey.Address(), updatedState3.NextValidators.Proposer.Address)
 
-	expectedVal1Prio2 := oldVal1.ProposerPriority + val1VotingPower
-	expectedVal2Prio2 := oldVal2.ProposerPriority + val1VotingPower - totalPower
-	avgSum = big.NewInt(expectedVal1Prio + expectedVal2Prio)
-	avg = avgSum.Div(avgSum, big.NewInt(2))
-	expectedVal1Prio -= avg.Int64()
-	expectedVal2Prio -= avg.Int64()
+	// check if expected proposer prio is matched:
+	// Increment
+	expectedVal2Prio2 := expectedVal2Prio + val2VotingPower // -1 + 10 = 9
+	expectedVal1Prio2 := expectedVal1Prio + val1VotingPower // 1 + 10 == 11
+	expectedVal1Prio2 = expectedVal1Prio2 - totalPower      // -9, val1 proposer
 
-	// -19 + 10 - 0 (avg) == -9
 	assert.EqualValues(t, expectedVal1Prio2, updatedVal1.ProposerPriority, "unexpected proposer priority for validator: %v", updatedVal2)
-	// 0 + 10 - 0 (avg) - 20 (total) == -10
 	assert.EqualValues(t, expectedVal2Prio2, updatedVal2.ProposerPriority, "unexpected proposer priority for validator: %v", updatedVal2)
 
 	// no changes in voting power and both validators have same voting power
 	// -> proposers should alternate:
 	oldState := updatedState3
+	abciResponses = &ABCIResponses{
+		EndBlock: &abci.ResponseEndBlock{ValidatorUpdates: nil},
+	}
+	validatorUpdates, err = types.PB2TM.ValidatorUpdates(abciResponses.EndBlock.ValidatorUpdates)
+	require.NoError(t, err)
+
+	oldState, err = updateState(oldState, blockID, &block.Header, abciResponses, validatorUpdates)
+	assert.NoError(t, err)
+	expectedVal1Prio2 = 1
+	expectedVal2Prio2 = -1
+	expectedVal1Prio = -9
+	expectedVal2Prio = 9
+
 	for i := 0; i < 1000; i++ {
 		// no validator updates:
 		abciResponses := &ABCIResponses{

types/validator.go

@@ -3,6 +3,7 @@ package types
 import (
 	"bytes"
 	"fmt"
+	"strings"
 
 	"github.com/tendermint/tendermint/crypto"
 	cmn "github.com/tendermint/tendermint/libs/common"
@@ -68,6 +69,16 @@ func (v *Validator) String() string {
 		v.ProposerPriority)
 }
 
+// ValidatorListString returns a prettified validator list for logging purposes.
+func ValidatorListString(vals []*Validator) string {
+	chunks := make([]string, len(vals))
+	for i, val := range vals {
+		chunks[i] = fmt.Sprintf("%s:%d", val.Address, val.VotingPower)
+	}
+
+	return strings.Join(chunks, ",")
+}
+
 // Bytes computes the unique encoding of a validator with a given voting power.
 // These are the bytes that gets hashed in consensus. It excludes address
 // as its redundant with the pubkey. This also excludes ProposerPriority

types/validator_set.go

@@ -12,14 +12,20 @@ import (
 	cmn "github.com/tendermint/tendermint/libs/common"
 )
 
-// The maximum allowed total voting power.
-// It needs to be sufficiently small to, in all cases::
+// MaxTotalVotingPower - the maximum allowed total voting power.
+// It needs to be sufficiently small to, in all cases:
 // 1. prevent clipping in incrementProposerPriority()
-// 2. let (diff+diffMax-1) not overflow in IncrementPropposerPriotity()
+// 2. let (diff+diffMax-1) not overflow in IncrementProposerPriority()
 // (Proof of 1 is tricky, left to the reader).
 // It could be higher, but this is sufficiently large for our purposes,
 // and leaves room for defensive purposes.
-const MaxTotalVotingPower = int64(math.MaxInt64) / 8
+// PriorityWindowSizeFactor - is a constant that when multiplied with the total voting power gives
+// the maximum allowed distance between validator priorities.
+
+const (
+	MaxTotalVotingPower      = int64(math.MaxInt64) / 8
+	PriorityWindowSizeFactor = 2
+)
 
 // ValidatorSet represent a set of *Validator at a given height.
 // The validators can be fetched by address or index.
@@ -42,19 +48,17 @@ type ValidatorSet struct {
 // NewValidatorSet initializes a ValidatorSet by copying over the
 // values from `valz`, a list of Validators. If valz is nil or empty,
 // the new ValidatorSet will have an empty list of Validators.
+// The addresses of validators in `valz` must be unique otherwise the
+// function panics.
 func NewValidatorSet(valz []*Validator) *ValidatorSet {
-	validators := make([]*Validator, len(valz))
-	for i, val := range valz {
-		validators[i] = val.Copy()
-	}
-	sort.Sort(ValidatorsByAddress(validators))
-	vals := &ValidatorSet{
-		Validators: validators,
+	vals := &ValidatorSet{}
+	err := vals.updateWithChangeSet(valz, false)
+	if err != nil {
+		panic(fmt.Sprintf("cannot create validator set: %s", err))
 	}
 	if len(valz) > 0 {
 		vals.IncrementProposerPriority(1)
 	}
-
 	return vals
 }
 
@@ -74,6 +78,9 @@ func (vals *ValidatorSet) CopyIncrementProposerPriority(times int) *ValidatorSet
 // proposer. Panics if validator set is empty.
 // `times` must be positive.
 func (vals *ValidatorSet) IncrementProposerPriority(times int) {
+	if vals.IsNilOrEmpty() {
+		panic("empty validator set")
+	}
 	if times <= 0 {
 		panic("Cannot call IncrementProposerPriority with non-positive times")
 	}
@@ -81,20 +88,23 @@ func (vals *ValidatorSet) IncrementProposerPriority(times int) {
 	// Cap the difference between priorities to be proportional to 2*totalPower by
 	// re-normalizing priorities, i.e., rescale all priorities by multiplying with:
 	//  2*totalVotingPower/(maxPriority - minPriority)
-	diffMax := 2 * vals.TotalVotingPower()
+	diffMax := PriorityWindowSizeFactor * vals.TotalVotingPower()
 	vals.RescalePriorities(diffMax)
+	vals.shiftByAvgProposerPriority()
 
 	var proposer *Validator
 	// call IncrementProposerPriority(1) times times:
 	for i := 0; i < times; i++ {
 		proposer = vals.incrementProposerPriority()
 	}
-	vals.shiftByAvgProposerPriority()
 
 	vals.Proposer = proposer
 }
 
 func (vals *ValidatorSet) RescalePriorities(diffMax int64) {
+	if vals.IsNilOrEmpty() {
+		panic("empty validator set")
+	}
 	// NOTE: This check is merely a sanity check which could be
 	// removed if all tests would init. voting power appropriately;
 	// i.e. diffMax should always be > 0
@@ -102,7 +112,7 @@ func (vals *ValidatorSet) RescalePriorities(diffMax int64) {
 		return
 	}
 
-	// Caculating ceil(diff/diffMax):
+	// Calculating ceil(diff/diffMax):
 	// Re-normalization is performed by dividing by an integer for simplicity.
 	// NOTE: This may make debugging priority issues easier as well.
 	diff := computeMaxMinPriorityDiff(vals)
@@ -146,6 +156,9 @@ func (vals *ValidatorSet) computeAvgProposerPriority() int64 {
 
 // compute the difference between the max and min ProposerPriority of that set
 func computeMaxMinPriorityDiff(vals *ValidatorSet) int64 {
+	if vals.IsNilOrEmpty() {
+		panic("empty validator set")
+	}
 	max := int64(math.MinInt64)
 	min := int64(math.MaxInt64)
 	for _, v := range vals.Validators {
@@ -173,21 +186,31 @@ func (vals *ValidatorSet) getValWithMostPriority() *Validator {
 }
 
 func (vals *ValidatorSet) shiftByAvgProposerPriority() {
+	if vals.IsNilOrEmpty() {
+		panic("empty validator set")
+	}
 	avgProposerPriority := vals.computeAvgProposerPriority()
 	for _, val := range vals.Validators {
 		val.ProposerPriority = safeSubClip(val.ProposerPriority, avgProposerPriority)
 	}
 }
 
+// Makes a copy of the validator list
+func validatorListCopy(valsList []*Validator) []*Validator {
+	if valsList == nil {
+		return nil
+	}
+	valsCopy := make([]*Validator, len(valsList))
+	for i, val := range valsList {
+		valsCopy[i] = val.Copy()
+	}
+	return valsCopy
+}
+
 // Copy each validator into a new ValidatorSet
 func (vals *ValidatorSet) Copy() *ValidatorSet {
-	validators := make([]*Validator, len(vals.Validators))
-	for i, val := range vals.Validators {
-		// NOTE: must copy, since IncrementProposerPriority updates in place.
-		validators[i] = val.Copy()
-	}
 	return &ValidatorSet{
-		Validators:       validators,
+		Validators:       validatorListCopy(vals.Validators),
 		Proposer:         vals.Proposer,
 		totalVotingPower: vals.totalVotingPower,
 	}
@@ -284,57 +307,6 @@ func (vals *ValidatorSet) Hash() []byte {
 	return merkle.SimpleHashFromByteSlices(bzs)
 }
 
-// Add adds val to the validator set and returns true. It returns false if val
-// is already in the set.
-func (vals *ValidatorSet) Add(val *Validator) (added bool) {
-	val = val.Copy()
-	idx := sort.Search(len(vals.Validators), func(i int) bool {
-		return bytes.Compare(val.Address, vals.Validators[i].Address) <= 0
-	})
-	if idx >= len(vals.Validators) {
-		vals.Validators = append(vals.Validators, val)
-		// Invalidate cache
-		vals.Proposer = nil
-		vals.totalVotingPower = 0
-		return true
-	} else if bytes.Equal(vals.Validators[idx].Address, val.Address) {
-		return false
-	} else {
-		newValidators := make([]*Validator, len(vals.Validators)+1)
-		copy(newValidators[:idx], vals.Validators[:idx])
-		newValidators[idx] = val
-		copy(newValidators[idx+1:], vals.Validators[idx:])
-		vals.Validators = newValidators
-		// Invalidate cache
-		vals.Proposer = nil
-		vals.totalVotingPower = 0
-		return true
-	}
-}
-
-// Update updates the ValidatorSet by copying in the val.
-// If the val is not found, it returns false; otherwise,
-// it returns true. The val.ProposerPriority field is ignored
-// and unchanged by this method.
-func (vals *ValidatorSet) Update(val *Validator) (updated bool) {
-	index, sameVal := vals.GetByAddress(val.Address)
-	if sameVal == nil {
-		return false
-	}
-	// Overwrite the ProposerPriority so it doesn't change.
-	// During block execution, the val passed in here comes
-	// from ABCI via PB2TM.ValidatorUpdates. Since ABCI
-	// doesn't know about ProposerPriority, PB2TM.ValidatorUpdates
-	// uses the default value of 0, which would cause issues for
-	// proposer selection every time a validator's voting power changes.
-	val.ProposerPriority = sameVal.ProposerPriority
-	vals.Validators[index] = val.Copy()
-	// Invalidate cache
-	vals.Proposer = nil
-	vals.totalVotingPower = 0
-	return true
-}
-
 // Remove deletes the validator with address. It returns the validator removed
 // and true. If returns nil and false if validator is not present in the set.
 func (vals *ValidatorSet) Remove(address []byte) (val *Validator, removed bool) {
@@ -366,6 +338,253 @@ func (vals *ValidatorSet) Iterate(fn func(index int, val *Validator) bool) {
 	}
 }
 
+// Checks changes against duplicates, splits the changes in updates and removals, sorts them by address
+//
+// Returns:
+// updates, removals - the sorted lists of updates and removals
+// err - non-nil if duplicate entries or entries with negative voting power are seen
+//
+// No changes are made to 'origChanges'
+func processChanges(origChanges []*Validator) (updates, removals []*Validator, err error) {
+	// Make a deep copy of the changes and sort by address
+	changes := validatorListCopy(origChanges)
+	sort.Sort(ValidatorsByAddress(changes))
+
+	removals = make([]*Validator, 0, len(changes))
+	updates = make([]*Validator, 0, len(changes))
+	var prevAddr Address
+
+	// Scan changes by address and append valid validators to updates or removals lists
+	for _, valUpdate := range changes {
+		if bytes.Equal(valUpdate.Address, prevAddr) {
+			err = fmt.Errorf("duplicate entry %v in %v", valUpdate, changes)
+			return nil, nil, err
+		}
+		if valUpdate.VotingPower < 0 {
+			err = fmt.Errorf("voting power can't be negative %v", valUpdate)
+			return nil, nil, err
+		}
+		if valUpdate.VotingPower == 0 {
+			removals = append(removals, valUpdate)
+		} else {
+			updates = append(updates, valUpdate)
+		}
+		prevAddr = valUpdate.Address
+	}
+	return updates, removals, err
+}
+
+// Verifies a list of updates against a validator set, making sure the allowed
+// total voting power would not be exceeded if these updates would be applied to the set.
+// It also computes the total voting power of the set that would result after the updates but
+// before the removals.
+//
+// Returns:
+// updatedTotalVotingPower - the new total voting power if these updates would be applied
+// err - non-nil if the maximum allowed total voting power would be exceeded
+//
+// 'updates' should be a list of proper validator changes, i.e. they have been scanned
+// by processChanges for duplicates and invalid values.
+// No changes are made to the validator set 'vals'.
+func verifyUpdates(updates []*Validator, vals *ValidatorSet) (updatedTotalVotingPower int64, err error) {
+
+	// Scan the updates, compute new total voting power, check for overflow
+	updatedTotalVotingPower = vals.TotalVotingPower()
+
+	for _, valUpdate := range updates {
+		address := valUpdate.Address
+		_, val := vals.GetByAddress(address)
+		if val == nil {
+			// new validator, add its voting power the the total
+			updatedTotalVotingPower += valUpdate.VotingPower
+		} else {
+			// updated validator, add the difference in power to the total
+			updatedTotalVotingPower += valUpdate.VotingPower - val.VotingPower
+		}
+
+		if updatedTotalVotingPower < 0 {
+			err = fmt.Errorf(
+				"failed to add/update validator with negative voting power %v",
+				valUpdate)
+			return 0, err
+		}
+		overflow := updatedTotalVotingPower > MaxTotalVotingPower
+		if overflow {
+			err = fmt.Errorf(
+				"failed to add/update validator %v, total voting power would exceed the max allowed %v",
+				valUpdate, MaxTotalVotingPower)
+			return 0, err
+		}
+	}
+
+	return updatedTotalVotingPower, nil
+}
+
+// Computes the proposer priority for the validators not present in the set based on 'updatedTotalVotingPower'
+// Leaves unchanged the priorities of validators that are changed.
+//
+// 'updates' parameter must be a list of unique validators to be added or updated.
+// No changes are made to the validator set 'vals'.
+func computeNewPriorities(updates []*Validator, vals *ValidatorSet, updatedTotalVotingPower int64) int {
+
+	numNew := 0
+	// Scan and update the proposerPriority for newly added and updated validators
+	for _, valUpdate := range updates {
+		address := valUpdate.Address
+		_, val := vals.GetByAddress(address)
+		if val == nil {
+			// add val
+			// Set ProposerPriority to -C*totalVotingPower (with C ~= 1.125) to make sure validators can't
+			// un-bond and then re-bond to reset their (potentially previously negative) ProposerPriority to zero.
+			//
+			// Contract: updatedVotingPower < MaxTotalVotingPower to ensure ProposerPriority does
+			// not exceed the bounds of int64.
+			//
+			// Compute ProposerPriority = -1.125*totalVotingPower == -(updatedVotingPower + (updatedVotingPower >> 3)).
+			valUpdate.ProposerPriority = -(updatedTotalVotingPower + (updatedTotalVotingPower >> 3))
+			numNew++
+		} else {
+			valUpdate.ProposerPriority = val.ProposerPriority
+		}
+	}
+
+	return numNew
+}
+
+// Merges the vals' validator list with the updates list.
+// When two elements with same address are seen, the one from updates is selected.
+// Expects updates to be a list of updates sorted by address with no duplicates or errors,
+// must have been validated with verifyUpdates() and priorities computed with computeNewPriorities().
+func (vals *ValidatorSet) applyUpdates(updates []*Validator) {
+
+	existing := make([]*Validator, len(vals.Validators))
+	copy(existing, vals.Validators)
+
+	merged := make([]*Validator, len(existing)+len(updates))
+	i := 0
+
+	for len(existing) > 0 && len(updates) > 0 {
+		if bytes.Compare(existing[0].Address, updates[0].Address) < 0 {
+			merged[i] = existing[0]
+			existing = existing[1:]
+		} else {
+			merged[i] = updates[0]
+			if bytes.Equal(existing[0].Address, updates[0].Address) {
+				// validator present in both, advance existing
+				existing = existing[1:]
+			}
+			updates = updates[1:]
+		}
+		i++
+	}
+
+	for j := 0; j < len(existing); j++ {
+		merged[i] = existing[j]
+		i++
+	}
+
+	for j := 0; j < len(updates); j++ {
+		merged[i] = updates[j]
+		i++
+	}
+
+	vals.Validators = merged[:i]
+	vals.totalVotingPower = 0
+}
+
+// Checks that the validators to be removed are part of the validator set.
+// No changes are made to the validator set 'vals'.
+func verifyRemovals(deletes []*Validator, vals *ValidatorSet) error {
+
+	for _, valUpdate := range deletes {
+		address := valUpdate.Address
+		_, val := vals.GetByAddress(address)
+		if val == nil {
+			return fmt.Errorf("failed to find validator %X to remove", address)
+		}
+	}
+	return nil
+}
+
+// Removes the validators specified in 'deletes' from validator set 'vals'.
+// Should not fail as verification has been done before.
+func (vals *ValidatorSet) applyRemovals(deletes []*Validator) {
+
+	for _, valUpdate := range deletes {
+		address := valUpdate.Address
+		_, removed := vals.Remove(address)
+		if !removed {
+			// Should never happen
+			panic(fmt.Sprintf("failed to remove validator %X", address))
+		}
+	}
+}
+
+// UpdateWithChangeSet attempts to update the validator set with 'changes'
+// It performs the following steps:
+// - validates the changes making sure there are no duplicates and splits them in updates and deletes
+// - verifies that applying the changes will not result in errors
+// - computes the total voting power BEFORE removals to ensure that in the next steps the relative priorities
+//   across old and newly added validators is fair
+// - computes the priorities of new validators against the final set
+// - applies the updates against the validator set
+// - applies the removals against the validator set
+// - performs scaling and centering of priority values
+// If error is detected during verification steps it is returned and the validator set
+// is not changed.
+func (vals *ValidatorSet) UpdateWithChangeSet(changes []*Validator) error {
+	return vals.updateWithChangeSet(changes, true)
+}
+
+// main function used by UpdateWithChangeSet() and NewValidatorSet()
+// If 'allowDeletes' is false then delete operations are not allowed and must be reported if
+// present in 'changes'
+func (vals *ValidatorSet) updateWithChangeSet(changes []*Validator, allowDeletes bool) error {
+
+	if len(changes) <= 0 {
+		return nil
+	}
+
+	// Check for duplicates within changes, split in 'updates' and 'deletes' lists (sorted)
+	updates, deletes, err := processChanges(changes)
+	if err != nil {
+		return err
+	}
+
+	if !allowDeletes && len(deletes) != 0 {
+		err = fmt.Errorf("cannot process validators with voting power 0: %v", deletes)
+		return err
+	}
+
+	// Verify that applying the 'deletes' against 'vals' will not result in error.
+	if err := verifyRemovals(deletes, vals); err != nil {
+		return err
+	}
+
+	// Verify that applying the 'updates' against 'vals' will not result in error.
+	updatedTotalVotingPower, err := verifyUpdates(updates, vals)
+	if err != nil {
+		return err
+	}
+
+	// Compute the priorities for updates
+	numNewValidators := computeNewPriorities(updates, vals, updatedTotalVotingPower)
+	if len(vals.Validators)+numNewValidators <= len(deletes) {
+		err = fmt.Errorf("applying the validator changes would result in empty set")
+		return err
+	}
+
+	// Apply updates and removals
+	vals.applyUpdates(updates)
+	vals.applyRemovals(deletes)
+
+	// Scale and center
+	vals.RescalePriorities(PriorityWindowSizeFactor * vals.TotalVotingPower())
+	vals.shiftByAvgProposerPriority()
+
+	return nil
+}
+
 // Verify that +2/3 of the set had signed the given signBytes.
 func (vals *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height int64, commit *Commit) error {
 

types/validator_set_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"math"
+	"math/rand"
 	"strings"
 	"testing"
 	"testing/quick"
@@ -45,31 +46,29 @@ func TestValidatorSetBasic(t *testing.T) {
 	assert.Nil(t, vset.Hash())
 
 	// add
-
 	val = randValidator_(vset.TotalVotingPower())
-	assert.True(t, vset.Add(val))
+	assert.NoError(t, vset.UpdateWithChangeSet([]*Validator{val}))
+
 	assert.True(t, vset.HasAddress(val.Address))
-	idx, val2 := vset.GetByAddress(val.Address)
+	idx, _ = vset.GetByAddress(val.Address)
 	assert.Equal(t, 0, idx)
-	assert.Equal(t, val, val2)
-	addr, val2 = vset.GetByIndex(0)
+	addr, _ = vset.GetByIndex(0)
 	assert.Equal(t, []byte(val.Address), addr)
-	assert.Equal(t, val, val2)
 	assert.Equal(t, 1, vset.Size())
 	assert.Equal(t, val.VotingPower, vset.TotalVotingPower())
-	assert.Equal(t, val, vset.GetProposer())
 	assert.NotNil(t, vset.Hash())
 	assert.NotPanics(t, func() { vset.IncrementProposerPriority(1) })
+	assert.Equal(t, val.Address, vset.GetProposer().Address)
 
 	// update
-	assert.False(t, vset.Update(randValidator_(vset.TotalVotingPower())))
+	val = randValidator_(vset.TotalVotingPower())
+	assert.NoError(t, vset.UpdateWithChangeSet([]*Validator{val}))
 	_, val = vset.GetByAddress(val.Address)
 	val.VotingPower += 100
 	proposerPriority := val.ProposerPriority
-	// Mimic update from types.PB2TM.ValidatorUpdates which does not know about ProposerPriority
-	// and hence defaults to 0.
+
 	val.ProposerPriority = 0
-	assert.True(t, vset.Update(val))
+	assert.NoError(t, vset.UpdateWithChangeSet([]*Validator{val}))
 	_, val = vset.GetByAddress(val.Address)
 	assert.Equal(t, proposerPriority, val.ProposerPriority)
 
@@ -116,8 +115,9 @@ func BenchmarkValidatorSetCopy(b *testing.B) {
 	for i := 0; i < 1000; i++ {
 		privKey := ed25519.GenPrivKey()
 		pubKey := privKey.PubKey()
-		val := NewValidator(pubKey, 0)
-		if !vset.Add(val) {
+		val := NewValidator(pubKey, 10)
+		err := vset.UpdateWithChangeSet([]*Validator{val})
+		if err != nil {
 			panic("Failed to add validator")
 		}
 	}
@@ -284,7 +284,7 @@ func randPubKey() crypto.PubKey {
 func randValidator_(totalVotingPower int64) *Validator {
 	// this modulo limits the ProposerPriority/VotingPower to stay in the
 	// bounds of MaxTotalVotingPower minus the already existing voting power:
-	val := NewValidator(randPubKey(), cmn.RandInt64()%(MaxTotalVotingPower-totalVotingPower))
+	val := NewValidator(randPubKey(), int64(cmn.RandUint64()%uint64((MaxTotalVotingPower-totalVotingPower))))
 	val.ProposerPriority = cmn.RandInt64() % (MaxTotalVotingPower - totalVotingPower)
 	return val
 }
@@ -599,3 +599,357 @@ func TestValidatorSetVerifyCommit(t *testing.T) {
 	err = vset.VerifyCommit(chainID, blockID, height, commit)
 	assert.Nil(t, err)
 }
+
+func TestEmptySet(t *testing.T) {
+
+	var valList []*Validator
+	valSet := NewValidatorSet(valList)
+	assert.Panics(t, func() { valSet.IncrementProposerPriority(1) })
+	assert.Panics(t, func() { valSet.RescalePriorities(100) })
+	assert.Panics(t, func() { valSet.shiftByAvgProposerPriority() })
+	assert.Panics(t, func() { assert.Zero(t, computeMaxMinPriorityDiff(valSet)) })
+	valSet.GetProposer()
+
+	// Add to empty set
+	v1 := newValidator([]byte("v1"), 100)
+	v2 := newValidator([]byte("v2"), 100)
+	valList = []*Validator{v1, v2}
+	assert.NoError(t, valSet.UpdateWithChangeSet(valList))
+	verifyValidatorSet(t, valSet)
+
+	// Delete all validators from set
+	v1 = newValidator([]byte("v1"), 0)
+	v2 = newValidator([]byte("v2"), 0)
+	delList := []*Validator{v1, v2}
+	assert.Error(t, valSet.UpdateWithChangeSet(delList))
+
+	// Attempt delete from empty set
+	assert.Error(t, valSet.UpdateWithChangeSet(delList))
+
+}
+
+func TestUpdatesForNewValidatorSet(t *testing.T) {
+
+	v1 := newValidator([]byte("v1"), 100)
+	v2 := newValidator([]byte("v2"), 100)
+	valList := []*Validator{v1, v2}
+	valSet := NewValidatorSet(valList)
+	verifyValidatorSet(t, valSet)
+
+	// Verify duplicates are caught in NewValidatorSet() and it panics
+	v111 := newValidator([]byte("v1"), 100)
+	v112 := newValidator([]byte("v1"), 123)
+	v113 := newValidator([]byte("v1"), 234)
+	valList = []*Validator{v111, v112, v113}
+	assert.Panics(t, func() { NewValidatorSet(valList) })
+
+	// Verify set including validator with voting power 0 cannot be created
+	v1 = newValidator([]byte("v1"), 0)
+	v2 = newValidator([]byte("v2"), 22)
+	v3 := newValidator([]byte("v3"), 33)
+	valList = []*Validator{v1, v2, v3}
+	assert.Panics(t, func() { NewValidatorSet(valList) })
+
+	// Verify set including validator with negative voting power cannot be created
+	v1 = newValidator([]byte("v1"), 10)
+	v2 = newValidator([]byte("v2"), -20)
+	v3 = newValidator([]byte("v3"), 30)
+	valList = []*Validator{v1, v2, v3}
+	assert.Panics(t, func() { NewValidatorSet(valList) })
+
+}
+
+type testVal struct {
+	name  string
+	power int64
+}
+
+func TestValSetUpdatesBasicTestsExecute(t *testing.T) {
+	valSetUpdatesBasicTests := []struct {
+		startVals    []testVal
+		updateVals   []testVal
+		expectedVals []testVal
+		expError     bool
+	}{
+		// Operations that should result in error
+		0: { // updates leading to overflows
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v1", math.MaxInt64}},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			true},
+		1: { // duplicate entries in changes
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v1", 11}, {"v1", 22}},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			true},
+		2: { // duplicate entries in removes
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v1", 0}, {"v1", 0}},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			true},
+		3: { // duplicate entries in removes + changes
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v1", 0}, {"v2", 20}, {"v2", 30}, {"v1", 0}},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			true},
+		4: { // update with negative voting power
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v1", -123}},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			true},
+		5: { // delete non existing validator
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v3", 0}},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			true},
+
+		// Operations that should be successful
+		6: { // no changes
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{},
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			false},
+		7: { // voting power changes
+			[]testVal{{"v1", 10}, {"v2", 10}},
+			[]testVal{{"v1", 11}, {"v2", 22}},
+			[]testVal{{"v1", 11}, {"v2", 22}},
+			false},
+		8: { // add new validators
+			[]testVal{{"v1", 10}, {"v2", 20}},
+			[]testVal{{"v3", 30}, {"v4", 40}},
+			[]testVal{{"v1", 10}, {"v2", 20}, {"v3", 30}, {"v4", 40}},
+			false},
+		9: { // delete validators
+			[]testVal{{"v1", 10}, {"v2", 20}, {"v3", 30}},
+			[]testVal{{"v2", 0}},
+			[]testVal{{"v1", 10}, {"v3", 30}},
+			false},
+		10: { // delete all validators
+			[]testVal{{"v1", 10}, {"v2", 20}, {"v3", 30}},
+			[]testVal{{"v1", 0}, {"v2", 0}, {"v3", 0}},
+			[]testVal{{"v1", 10}, {"v2", 20}, {"v3", 30}},
+			true},
+	}
+
+	for i, tt := range valSetUpdatesBasicTests {
+		// create a new set and apply updates, keeping copies for the checks
+		valSet := createNewValidatorSet(tt.startVals)
+		valSetCopy := valSet.Copy()
+		valList := createNewValidatorList(tt.updateVals)
+		valListCopy := validatorListCopy(valList)
+		err := valSet.UpdateWithChangeSet(valList)
+
+		if tt.expError {
+			// for errors check the validator set has not been changed
+			assert.Error(t, err, "test %d", i)
+			assert.Equal(t, valSet, valSetCopy, "test %v", i)
+		} else {
+			assert.NoError(t, err, "test %d", i)
+		}
+		// check the parameter list has not changed
+		assert.Equal(t, valList, valListCopy, "test %v", i)
+
+		// check the final validator list is as expected and the set is properly scaled and centered.
+		assert.Equal(t, getValidatorResults(valSet.Validators), tt.expectedVals, "test %v", i)
+		verifyValidatorSet(t, valSet)
+	}
+}
+
+func getValidatorResults(valList []*Validator) []testVal {
+	testList := make([]testVal, len(valList))
+	for i, val := range valList {
+		testList[i].name = string(val.Address)
+		testList[i].power = val.VotingPower
+	}
+	return testList
+}
+
+// Test that different permutations of an update give the same result.
+func TestValSetUpdatesOrderTestsExecute(t *testing.T) {
+	// startVals - initial validators to create the set with
+	// updateVals - a sequence of updates to be applied to the set.
+	// updateVals is shuffled a number of times during testing to check for same resulting validator set.
+	valSetUpdatesOrderTests := []struct {
+		startVals  []testVal
+		updateVals []testVal
+	}{
+		0: { // order of changes should not matter, the final validator sets should be the same
+			[]testVal{{"v1", 10}, {"v2", 10}, {"v3", 30}, {"v4", 40}},
+			[]testVal{{"v1", 11}, {"v2", 22}, {"v3", 33}, {"v4", 44}}},
+
+		1: { // order of additions should not matter
+			[]testVal{{"v1", 10}, {"v2", 20}},
+			[]testVal{{"v3", 30}, {"v4", 40}, {"v5", 50}, {"v6", 60}}},
+
+		2: { // order of removals should not matter
+			[]testVal{{"v1", 10}, {"v2", 20}, {"v3", 30}, {"v4", 40}},
+			[]testVal{{"v1", 0}, {"v3", 0}, {"v4", 0}}},
+
+		3: { // order of mixed operations should not matter
+			[]testVal{{"v1", 10}, {"v2", 20}, {"v3", 30}, {"v4", 40}},
+			[]testVal{{"v1", 0}, {"v3", 0}, {"v2", 22}, {"v5", 50}, {"v4", 44}}},
+	}
+
+	for i, tt := range valSetUpdatesOrderTests {
+		// create a new set and apply updates
+		valSet := createNewValidatorSet(tt.startVals)
+		valSetCopy := valSet.Copy()
+		valList := createNewValidatorList(tt.updateVals)
+		assert.NoError(t, valSetCopy.UpdateWithChangeSet(valList))
+
+		// save the result as expected for next updates
+		valSetExp := valSetCopy.Copy()
+
+		// perform at most 20 permutations on the updates and call UpdateWithChangeSet()
+		n := len(tt.updateVals)
+		maxNumPerms := cmn.MinInt(20, n*n)
+		for j := 0; j < maxNumPerms; j++ {
+			// create a copy of original set and apply a random permutation of updates
+			valSetCopy := valSet.Copy()
+			valList := createNewValidatorList(permutation(tt.updateVals))
+
+			// check there was no error and the set is properly scaled and centered.
+			assert.NoError(t, valSetCopy.UpdateWithChangeSet(valList),
+				"test %v failed for permutation %v", i, valList)
+			verifyValidatorSet(t, valSetCopy)
+
+			// verify the resulting test is same as the expected
+			assert.Equal(t, valSetCopy, valSetExp,
+				"test %v failed for permutation %v", i, valList)
+		}
+	}
+}
+
+// This tests the private function validator_set.go:applyUpdates() function, used only for additions and changes.
+// Should perform a proper merge of updatedVals and startVals
+func TestValSetApplyUpdatesTestsExecute(t *testing.T) {
+	valSetUpdatesBasicTests := []struct {
+		startVals    []testVal
+		updateVals   []testVal
+		expectedVals []testVal
+	}{
+		// additions
+		0: { // prepend
+			[]testVal{{"v4", 44}, {"v5", 55}},
+			[]testVal{{"v1", 11}},
+			[]testVal{{"v1", 11}, {"v4", 44}, {"v5", 55}}},
+		1: { // append
+			[]testVal{{"v4", 44}, {"v5", 55}},
+			[]testVal{{"v6", 66}},
+			[]testVal{{"v4", 44}, {"v5", 55}, {"v6", 66}}},
+		2: { // insert
+			[]testVal{{"v4", 44}, {"v6", 66}},
+			[]testVal{{"v5", 55}},
+			[]testVal{{"v4", 44}, {"v5", 55}, {"v6", 66}}},
+		3: { // insert multi
+			[]testVal{{"v4", 44}, {"v6", 66}, {"v9", 99}},
+			[]testVal{{"v5", 55}, {"v7", 77}, {"v8", 88}},
+			[]testVal{{"v4", 44}, {"v5", 55}, {"v6", 66}, {"v7", 77}, {"v8", 88}, {"v9", 99}}},
+		// changes
+		4: { // head
+			[]testVal{{"v1", 111}, {"v2", 22}},
+			[]testVal{{"v1", 11}},
+			[]testVal{{"v1", 11}, {"v2", 22}}},
+		5: { // tail
+			[]testVal{{"v1", 11}, {"v2", 222}},
+			[]testVal{{"v2", 22}},
+			[]testVal{{"v1", 11}, {"v2", 22}}},
+		6: { // middle
+			[]testVal{{"v1", 11}, {"v2", 222}, {"v3", 33}},
+			[]testVal{{"v2", 22}},
+			[]testVal{{"v1", 11}, {"v2", 22}, {"v3", 33}}},
+		7: { // multi
+			[]testVal{{"v1", 111}, {"v2", 222}, {"v3", 333}},
+			[]testVal{{"v1", 11}, {"v2", 22}, {"v3", 33}},
+			[]testVal{{"v1", 11}, {"v2", 22}, {"v3", 33}}},
+		// additions and changes
+		8: {
+			[]testVal{{"v1", 111}, {"v2", 22}},
+			[]testVal{{"v1", 11}, {"v3", 33}, {"v4", 44}},
+			[]testVal{{"v1", 11}, {"v2", 22}, {"v3", 33}, {"v4", 44}}},
+	}
+
+	for i, tt := range valSetUpdatesBasicTests {
+		// create a new validator set with the start values
+		valSet := createNewValidatorSet(tt.startVals)
+
+		// applyUpdates() with the update values
+		valList := createNewValidatorList(tt.updateVals)
+		valSet.applyUpdates(valList)
+
+		// check the new list of validators for proper merge
+		assert.Equal(t, getValidatorResults(valSet.Validators), tt.expectedVals, "test %v", i)
+		verifyValidatorSet(t, valSet)
+	}
+}
+
+func permutation(valList []testVal) []testVal {
+	if len(valList) == 0 {
+		return nil
+	}
+	permList := make([]testVal, len(valList))
+	perm := rand.Perm(len(valList))
+	for i, v := range perm {
+		permList[v] = valList[i]
+	}
+	return permList
+}
+
+func createNewValidatorList(testValList []testVal) []*Validator {
+	valList := make([]*Validator, 0, len(testValList))
+	for _, val := range testValList {
+		valList = append(valList, newValidator([]byte(val.name), val.power))
+	}
+	return valList
+}
+
+func createNewValidatorSet(testValList []testVal) *ValidatorSet {
+	valList := createNewValidatorList(testValList)
+	valSet := NewValidatorSet(valList)
+	return valSet
+}
+
+func verifyValidatorSet(t *testing.T, valSet *ValidatorSet) {
+	// verify that the vals' tvp is set to the sum of the all vals voting powers
+	tvp := valSet.TotalVotingPower()
+	assert.Equal(t, valSet.totalVotingPower, tvp,
+		"expected TVP %d. Got %d, valSet=%s", tvp, valSet.totalVotingPower, valSet)
+
+	// verify that validator priorities are centered
+	l := int64(len(valSet.Validators))
+	tpp := valSet.TotalVotingPower()
+	assert.True(t, tpp <= l || tpp >= -l,
+		"expected total priority in (-%d, %d). Got %d", l, l, tpp)
+
+	// verify that priorities are scaled
+	dist := computeMaxMinPriorityDiff(valSet)
+	assert.True(t, dist <= PriorityWindowSizeFactor*tvp,
+		"expected priority distance < %d. Got %d", PriorityWindowSizeFactor*tvp, dist)
+}
+
+func BenchmarkUpdates(b *testing.B) {
+	const (
+		n = 100
+		m = 2000
+	)
+	// Init with n validators
+	vs := make([]*Validator, n)
+	for j := 0; j < n; j++ {
+		vs[j] = newValidator([]byte(fmt.Sprintf("v%d", j)), 100)
+	}
+	valSet := NewValidatorSet(vs)
+	l := len(valSet.Validators)
+
+	// Make m new validators
+	newValList := make([]*Validator, m)
+	for j := 0; j < m; j++ {
+		newValList[j] = newValidator([]byte(fmt.Sprintf("v%d", j+l)), 1000)
+	}
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		// Add m validators to valSetCopy
+		valSetCopy := valSet.Copy()
+		assert.NoError(b, valSetCopy.UpdateWithChangeSet(newValList))
+	}
+}