config/core: allow to change the number of validators

Fixes #2320.

docs/node-configuration.md

@@ -197,6 +197,7 @@ protocol-related settings described in the table below.
 
 | Section | Type | Default value | Description | Notes |
 | --- | --- | --- | --- | --- |
+| CommitteeHistory | map[uint32]int | none | Number of committee members after given height, for example `{0: 1, 20: 4}` sets up a chain with one committee member since the genesis and then changes the setting to 4 committee members at the height of 20. `StandbyCommittee` committee setting must have the number of keys equal or exceeding the highest value in this option. Blocks numbers where the change happens must be divisble by the old and by the new values simultaneously. If not set, committee size is derived from the `StandbyCommittee` setting and never changes. |
 | KeepOnlyLatestState | `bool` | `false` | Specifies if MPT should only store latest state. If true, DB size will be smaller, but older roots won't be accessible. This value should remain the same for the same database. |
 | Magic | `uint32` | `0` | Magic number which uniquely identifies NEO network. |
 | MaxBlockSize | `uint32` | `262144` | Maximum block size in bytes. |
@@ -216,6 +217,7 @@ protocol-related settings described in the table below.
 | StandbyCommittee | `[]string` | [] | List of public keys of standby committee validators are chosen from. |
 | StateRootInHeader | `bool` | `false` | Enables storing state root in block header. | Experimental protocol extension! |
 | StateSyncInterval | `int` | `40000` | The number of blocks between state heights available for MPT state data synchronization. | `P2PStateExchangeExtensions` should be enabled to use this setting.  |
-| ValidatorsCount | `int` | `0` | Number of validators. |
+| ValidatorsCount | `int` | `0` | Number of validators set for the whole network lifetime, can't be set if `ValidatorsHistory` setting is used. |
+| ValidatorsHistory | map[uint32]int | none | Number of consensus nodes to use after given height (see `CommitteeHistory` also). Heights where the change occurs must be divisible by the number of committee members at that height. Can't be used with `ValidatorsCount` not equal to zero. |
 | VerifyBlocks | `bool` | `false` | Denotes whether to verify received blocks. |
 | VerifyTransactions | `bool` | `false` | Denotes whether to verify transactions in received blocks. |

pkg/config/protocol_config.go

@@ -3,6 +3,7 @@ package config
 import (
 	"errors"
 	"fmt"
+	"sort"
 
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
 	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
@@ -12,8 +13,10 @@ import (
 // ProtocolConfiguration represents the protocol config.
 type (
 	ProtocolConfiguration struct {
-		Magic       netmode.Magic `yaml:"Magic"`
+		// CommitteeHistory stores committee size change history (height: size).
-		MemPoolSize int           `yaml:"MemPoolSize"`
+		CommitteeHistory map[uint32]int `yaml:"CommitteeHistory"`
+		Magic            netmode.Magic  `yaml:"Magic"`
+		MemPoolSize      int            `yaml:"MemPoolSize"`
 
 		// InitialGASSupply is the amount of GAS generated in the genesis block.
 		InitialGASSupply fixedn.Fixed8 `yaml:"InitialGASSupply"`
@@ -57,6 +60,8 @@ type (
 		// It is valid only if P2PStateExchangeExtensions are enabled.
 		StateSyncInterval int `yaml:"StateSyncInterval"`
 		ValidatorsCount   int `yaml:"ValidatorsCount"`
+		// Validators stores history of changes to consensus node number (height: number).
+		ValidatorsHistory map[uint32]int `yaml:"ValidatorsHistory"`
 		// Whether to verify received blocks.
 		VerifyBlocks bool `yaml:"VerifyBlocks"`
 		// Whether to verify transactions in received blocks.
@@ -64,17 +69,114 @@ type (
 	}
 )
 
+// heightNumber is an auxiliary structure for configuration checks.
+type heightNumber struct {
+	h uint32
+	n int
+}
+
 // Validate checks ProtocolConfiguration for internal consistency and returns
 // error if anything inappropriate found. Other methods can rely on protocol
 // validity after this.
 func (p *ProtocolConfiguration) Validate() error {
-	if len(p.StandbyCommittee) < p.ValidatorsCount {
+	var err error
-		return errors.New("validators count can't exceed the size of StandbyCommittee")
+
-	}
 	for name := range p.NativeUpdateHistories {
 		if !nativenames.IsValid(name) {
 			return fmt.Errorf("NativeActivations configuration section contains unexpected native contract name: %s", name)
 		}
 	}
+	if p.ValidatorsCount != 0 && len(p.ValidatorsHistory) != 0 {
+		return errors.New("configuration should either have ValidatorsCount or ValidatorsHistory, not both")
+	}
+	if len(p.StandbyCommittee) < p.ValidatorsCount {
+		return errors.New("validators count can't exceed the size of StandbyCommittee")
+	}
+	var arr = make([]heightNumber, 0, len(p.CommitteeHistory))
+	for h, n := range p.CommitteeHistory {
+		if int(n) > len(p.StandbyCommittee) {
+			return fmt.Errorf("too small StandbyCommittee for required number of committee members at %d", h)
+		}
+		arr = append(arr, heightNumber{h, n})
+	}
+	if len(arr) != 0 {
+		err = sortCheckZero(arr, "CommitteeHistory")
+		if err != nil {
+			return err
+		}
+		for i, hn := range arr[1:] {
+			if int64(hn.h)%int64(hn.n) != 0 || int64(hn.h)%int64(arr[i].n) != 0 {
+				return fmt.Errorf("invalid CommitteeHistory: bad %d height for %d and %d committee", hn.h, hn.n, arr[i].n)
+			}
+		}
+	}
+	arr = arr[:0]
+	for h, n := range p.ValidatorsHistory {
+		if int(n) > len(p.StandbyCommittee) {
+			return fmt.Errorf("too small StandbyCommittee for required number of validators at %d", h)
+		}
+		arr = append(arr, heightNumber{h, n})
+	}
+	if len(arr) != 0 {
+		err = sortCheckZero(arr, "ValidatorsHistory")
+		if err != nil {
+			return err
+		}
+		for _, hn := range arr {
+			if int64(hn.n) > int64(p.GetCommitteeSize(hn.h)) {
+				return fmt.Errorf("requested number of validators is too big: %d at %d", hn.n, hn.h)
+			}
+			if int64(hn.h)%int64(p.GetCommitteeSize(hn.h)) != 0 {
+				return fmt.Errorf("validators number change is not aligned with committee change at %d", hn.h)
+			}
+		}
+	}
 	return nil
 }
+
+// sortCheckZero sorts heightNumber array and checks for zero height presence.
+func sortCheckZero(arr []heightNumber, field string) error {
+	sort.Slice(arr, func(i, j int) bool {
+		return arr[i].h < arr[j].h
+	})
+	if arr[0].h != 0 {
+		return fmt.Errorf("invalid %s: no height 0 specified", field)
+	}
+	return nil
+}
+
+// GetCommitteeSize returns the committee size for the given height. It implies
+// valid configuration file.
+func (p *ProtocolConfiguration) GetCommitteeSize(height uint32) int {
+	if len(p.CommitteeHistory) == 0 {
+		return len(p.StandbyCommittee)
+	}
+	return getBestFromMap(p.CommitteeHistory, height)
+}
+
+func getBestFromMap(dict map[uint32]int, height uint32) int {
+	var res int
+	var bestH = uint32(0)
+	for h, n := range dict {
+		if h >= bestH && h <= height {
+			res = n
+			bestH = h
+		}
+	}
+	return res
+}
+
+// GetNumOfCNs returns the number of validators for the given height.
+// It implies valid configuration file.
+func (p *ProtocolConfiguration) GetNumOfCNs(height uint32) int {
+	if len(p.ValidatorsHistory) == 0 {
+		return p.ValidatorsCount
+	}
+	return getBestFromMap(p.ValidatorsHistory, height)
+}
+
+// ShouldUpdateCommitteeAt answers the question of whether the committee
+// should be updated at the given height.
+func (p *ProtocolConfiguration) ShouldUpdateCommitteeAt(height uint32) bool {
+	return height%uint32(p.GetCommitteeSize(height)) == 0
+}

pkg/config/protocol_config_test.go

@@ -13,8 +13,118 @@ func TestProtocolConfigurationValidation(t *testing.T) {
 	require.Error(t, p.Validate())
 	p = &ProtocolConfiguration{
 		NativeUpdateHistories: map[string][]uint32{
-			"someContract": []uint32{0, 10},
+			"someContract": {0, 10},
 		},
 	}
 	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+		},
+		ValidatorsCount: 3,
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		ValidatorsCount:   4,
+		ValidatorsHistory: map[uint32]int{0: 4},
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 4},
+		ValidatorsHistory: map[uint32]int{0: 4, 1000: 5},
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 4, 1000: 5},
+		ValidatorsHistory: map[uint32]int{0: 4},
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 1, 999: 4},
+		ValidatorsHistory: map[uint32]int{0: 1},
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 1, 1000: 4},
+		ValidatorsHistory: map[uint32]int{0: 1, 999: 4},
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 1, 100: 4},
+		ValidatorsHistory: map[uint32]int{0: 4, 100: 4},
+	}
+	require.Error(t, p.Validate())
+	p = &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 1, 100: 4},
+		ValidatorsHistory: map[uint32]int{0: 1, 100: 4},
+	}
+	require.NoError(t, p.Validate())
+}
+
+func TestGetCommitteeAndCNs(t *testing.T) {
+	p := &ProtocolConfiguration{
+		StandbyCommittee: []string{
+			"02b3622bf4017bdfe317c58aed5f4c753f206b7db896046fa7d774bbc4bf7f8dc2",
+			"02103a7f7dd016558597f7960d27c516a4394fd968b9e65155eb4b013e4040406e",
+			"03d90c07df63e690ce77912e10ab51acc944b66860237b608c4f8f8309e71ee699",
+			"02a7bc55fe8684e0119768d104ba30795bdcc86619e864add26156723ed185cd62",
+		},
+		CommitteeHistory:  map[uint32]int{0: 1, 100: 4},
+		ValidatorsHistory: map[uint32]int{0: 1, 200: 4},
+	}
+	require.Equal(t, 1, p.GetCommitteeSize(0))
+	require.Equal(t, 1, p.GetCommitteeSize(99))
+	require.Equal(t, 4, p.GetCommitteeSize(100))
+	require.Equal(t, 4, p.GetCommitteeSize(101))
+	require.Equal(t, 4, p.GetCommitteeSize(200))
+	require.Equal(t, 4, p.GetCommitteeSize(201))
+	require.Equal(t, 1, p.GetNumOfCNs(0))
+	require.Equal(t, 1, p.GetNumOfCNs(100))
+	require.Equal(t, 1, p.GetNumOfCNs(101))
+	require.Equal(t, 1, p.GetNumOfCNs(199))
+	require.Equal(t, 4, p.GetNumOfCNs(200))
+	require.Equal(t, 4, p.GetNumOfCNs(201))
 }

pkg/consensus/consensus.go

@@ -16,7 +16,6 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/core/blockchainer"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop"
 	"github.com/nspcc-dev/neo-go/pkg/core/mempool"
-	"github.com/nspcc-dev/neo-go/pkg/core/native"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
@@ -48,6 +47,7 @@ const Category = "dBFT"
 type Ledger interface {
 	AddBlock(block *coreb.Block) error
 	ApplyPolicyToTxSet([]*transaction.Transaction) []*transaction.Transaction
+	GetConfig() config.ProtocolConfiguration
 	GetMemPool() *mempool.Pool
 	GetNextBlockValidators() ([]*keys.PublicKey, error)
 	GetStateModule() blockchainer.StateRoot
@@ -676,7 +676,8 @@ func (s *service) newBlockFromContext(ctx *dbft.Context) block.Block {
 
 	var validators keys.PublicKeys
 	var err error
-	if native.ShouldUpdateCommittee(ctx.BlockIndex, s.Chain) {
+	cfg := s.Chain.GetConfig()
+	if cfg.ShouldUpdateCommitteeAt(ctx.BlockIndex) {
 		validators, err = s.Chain.GetValidators()
 	} else {
 		validators, err = s.Chain.GetNextBlockValidators()
@@ -684,7 +685,7 @@ func (s *service) newBlockFromContext(ctx *dbft.Context) block.Block {
 	if err != nil {
 		s.log.Fatal(fmt.Sprintf("failed to get validators: %s", err.Error()))
 	}
-	script, err := smartcontract.CreateMultiSigRedeemScript(s.dbft.Context.M(), validators)
+	script, err := smartcontract.CreateDefaultMultiSigRedeemScript(validators)
 	if err != nil {
 		s.log.Fatal(fmt.Sprintf("failed to create multisignature script: %s", err.Error()))
 	}

pkg/consensus/consensus_test.go

@@ -88,7 +88,8 @@ func initServiceNextConsensus(t *testing.T, newAcc *wallet.Account, offset uint3
 	require.NoError(t, bc.PoolTx(tx))
 	srv.dbft.OnTimeout(timer.HV{Height: srv.dbft.Context.BlockIndex})
 
-	for i := srv.dbft.BlockIndex; !native.ShouldUpdateCommittee(i+offset, bc); i++ {
+	cfg := bc.GetConfig()
+	for i := srv.dbft.BlockIndex; !cfg.ShouldUpdateCommitteeAt(i + offset); i++ {
 		srv.dbft.OnTimeout(timer.HV{Height: srv.dbft.Context.BlockIndex})
 	}
 

pkg/core/blockchain.go

@@ -162,8 +162,11 @@ type Blockchain struct {
 
 	extensible atomic.Value
 
+	// knownValidatorsCount is the latest known validators count used
+	// for defaultBlockWitness.
+	knownValidatorsCount atomic.Value
 	// defaultBlockWitness stores transaction.Witness with m out of n multisig,
-	// where n = ValidatorsCount.
+	// where n = knownValidatorsCount.
 	defaultBlockWitness atomic.Value
 
 	stateRoot *stateroot.Module
@@ -1177,7 +1180,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 }
 
 func (bc *Blockchain) updateExtensibleWhitelist(height uint32) error {
-	updateCommittee := native.ShouldUpdateCommittee(height, bc)
+	updateCommittee := bc.config.ShouldUpdateCommitteeAt(height)
 	stateVals, sh, err := bc.contracts.Designate.GetDesignatedByRole(bc.dao, noderoles.StateValidator, height)
 	if err != nil {
 		return err
@@ -1787,14 +1790,17 @@ func (bc *Blockchain) ApplyPolicyToTxSet(txes []*transaction.Transaction) []*tra
 	}
 	maxBlockSize := bc.config.MaxBlockSize
 	maxBlockSysFee := bc.config.MaxBlockSystemFee
+	oldVC := bc.knownValidatorsCount.Load()
 	defaultWitness := bc.defaultBlockWitness.Load()
-	if defaultWitness == nil {
+	curVC := bc.config.GetNumOfCNs(bc.BlockHeight() + 1)
-		m := smartcontract.GetDefaultHonestNodeCount(bc.config.ValidatorsCount)
+	if oldVC == nil || oldVC != curVC {
+		m := smartcontract.GetDefaultHonestNodeCount(curVC)
 		verification, _ := smartcontract.CreateDefaultMultiSigRedeemScript(bc.contracts.NEO.GetNextBlockValidatorsInternal())
 		defaultWitness = transaction.Witness{
 			InvocationScript:   make([]byte, 66*m),
 			VerificationScript: verification,
 		}
+		bc.knownValidatorsCount.Store(curVC)
 		bc.defaultBlockWitness.Store(defaultWitness)
 	}
 	var (
@@ -2085,7 +2091,7 @@ func (bc *Blockchain) PoolTxWithData(t *transaction.Transaction, data interface{
 
 // GetStandByValidators returns validators from the configuration.
 func (bc *Blockchain) GetStandByValidators() keys.PublicKeys {
-	return bc.sbCommittee[:bc.config.ValidatorsCount].Copy()
+	return bc.sbCommittee[:bc.config.GetNumOfCNs(bc.BlockHeight())].Copy()
 }
 
 // GetStandByCommittee returns standby committee from the configuration.

pkg/core/blockchain_test.go

@@ -1828,6 +1828,81 @@ func TestBlockchain_InitWithIncompleteStateJump(t *testing.T) {
 	}
 }
 
+func TestChainWithVolatileNumOfValidators(t *testing.T) {
+	bc := newTestChainWithCustomCfg(t, func(c *config.Config) {
+		c.ProtocolConfiguration.ValidatorsCount = 0
+		c.ProtocolConfiguration.CommitteeHistory = map[uint32]int{
+			0:  1,
+			4:  4,
+			24: 6,
+		}
+		c.ProtocolConfiguration.ValidatorsHistory = map[uint32]int{
+			0: 1,
+			4: 4,
+		}
+		require.NoError(t, c.ProtocolConfiguration.Validate())
+	})
+	require.Equal(t, uint32(0), bc.BlockHeight())
+
+	priv0 := testchain.PrivateKeyByID(0)
+
+	vals, err := bc.GetValidators()
+	require.NoError(t, err)
+	script, err := smartcontract.CreateDefaultMultiSigRedeemScript(vals)
+	require.NoError(t, err)
+	curWit := transaction.Witness{
+		VerificationScript: script,
+	}
+	for i := 1; i < 26; i++ {
+		comm, err := bc.GetCommittee()
+		require.NoError(t, err)
+		if i < 5 {
+			require.Equal(t, 1, len(comm))
+		} else if i < 25 {
+			require.Equal(t, 4, len(comm))
+		} else {
+			require.Equal(t, 6, len(comm))
+		}
+		// Mimic consensus.
+		if bc.config.ShouldUpdateCommitteeAt(uint32(i)) {
+			vals, err = bc.GetValidators()
+		} else {
+			vals, err = bc.GetNextBlockValidators()
+		}
+		require.NoError(t, err)
+		if i < 4 {
+			require.Equalf(t, 1, len(vals), "at %d", i)
+		} else {
+			require.Equalf(t, 4, len(vals), "at %d", i)
+		}
+		require.NoError(t, err)
+		script, err := smartcontract.CreateDefaultMultiSigRedeemScript(vals)
+		require.NoError(t, err)
+		nextWit := transaction.Witness{
+			VerificationScript: script,
+		}
+		b := &block.Block{
+			Header: block.Header{
+				NextConsensus: nextWit.ScriptHash(),
+				Script:        curWit,
+			},
+		}
+		curWit = nextWit
+		b.PrevHash = bc.GetHeaderHash(i - 1)
+		b.Timestamp = uint64(time.Now().UTC().Unix())*1000 + uint64(i)
+		b.Index = uint32(i)
+		b.RebuildMerkleRoot()
+		if i < 5 {
+			signa := priv0.SignHashable(uint32(bc.config.Magic), b)
+			b.Script.InvocationScript = append([]byte{byte(opcode.PUSHDATA1), byte(len(signa))}, signa...)
+		} else {
+			b.Script.InvocationScript = testchain.Sign(b)
+		}
+		err = bc.AddBlock(b)
+		require.NoErrorf(t, err, "at %d", i)
+	}
+}
+
 func setSigner(tx *transaction.Transaction, h util.Uint160) {
 	tx.Signers = []transaction.Signer{{
 		Account: h,

pkg/core/native/native_neo.go

@@ -273,7 +273,8 @@ func (n *NEO) updateCache(cvs keysWithVotes, bc interop.Ledger) error {
 	}
 	n.committeeHash.Store(hash.Hash160(script))
 
-	nextVals := committee[:bc.GetConfig().ValidatorsCount].Copy()
+	cfg := bc.GetConfig()
+	nextVals := committee[:cfg.GetNumOfCNs(bc.BlockHeight()+1)].Copy()
 	sort.Sort(nextVals)
 	n.nextValidators.Store(nextVals)
 	return nil
@@ -298,16 +299,16 @@ func (n *NEO) updateCommittee(ic *interop.Context) error {
 	return ic.DAO.PutStorageItem(n.ID, prefixCommittee, cvs.Bytes())
 }
 
-// ShouldUpdateCommittee returns true if committee is updated at block h.
-func ShouldUpdateCommittee(h uint32, bc interop.Ledger) bool {
-	cfg := bc.GetConfig()
-	r := len(cfg.StandbyCommittee)
-	return h%uint32(r) == 0
-}
-
 // OnPersist implements Contract interface.
 func (n *NEO) OnPersist(ic *interop.Context) error {
-	if ShouldUpdateCommittee(ic.Block.Index, ic.Chain) {
+	cfg := ic.Chain.GetConfig()
+	if cfg.ShouldUpdateCommitteeAt(ic.Block.Index) {
+		oldKeys := n.nextValidators.Load().(keys.PublicKeys)
+		oldCom := n.committee.Load().(keysWithVotes)
+		if cfg.GetNumOfCNs(ic.Block.Index) != len(oldKeys) ||
+			cfg.GetCommitteeSize(ic.Block.Index) != len(oldCom) {
+			n.votesChanged.Store(true)
+		}
 		if err := n.updateCommittee(ic); err != nil {
 			return err
 		}
@@ -319,16 +320,17 @@ func (n *NEO) OnPersist(ic *interop.Context) error {
 func (n *NEO) PostPersist(ic *interop.Context) error {
 	gas := n.GetGASPerBlock(ic.DAO, ic.Block.Index)
 	pubs := n.GetCommitteeMembers()
-	committeeSize := len(ic.Chain.GetConfig().StandbyCommittee)
+	cfg := ic.Chain.GetConfig()
+	committeeSize := cfg.GetCommitteeSize(ic.Block.Index)
 	index := int(ic.Block.Index) % committeeSize
 	committeeReward := new(big.Int).Mul(gas, bigCommitteeRewardRatio)
 	n.GAS.mint(ic, pubs[index].GetScriptHash(), committeeReward.Div(committeeReward, big100), false)
 
-	if ShouldUpdateCommittee(ic.Block.Index, ic.Chain) {
+	if cfg.ShouldUpdateCommitteeAt(ic.Block.Index) {
 		var voterReward = new(big.Int).Set(bigVoterRewardRatio)
 		voterReward.Mul(voterReward, gas)
 		voterReward.Mul(voterReward, big.NewInt(voterRewardFactor*int64(committeeSize)))
-		var validatorsCount = ic.Chain.GetConfig().ValidatorsCount
+		var validatorsCount = cfg.GetNumOfCNs(ic.Block.Index)
 		voterReward.Div(voterReward, big.NewInt(int64(committeeSize+validatorsCount)))
 		voterReward.Div(voterReward, big100)
 
@@ -938,14 +940,16 @@ func (n *NEO) getAccountState(ic *interop.Context, args []stackitem.Item) stacki
 
 // ComputeNextBlockValidators returns an actual list of current validators.
 func (n *NEO) ComputeNextBlockValidators(bc interop.Ledger, d dao.DAO) (keys.PublicKeys, error) {
-	if vals := n.validators.Load().(keys.PublicKeys); vals != nil {
+	cfg := bc.GetConfig()
+	numOfCNs := cfg.GetNumOfCNs(bc.BlockHeight() + 1)
+	if vals := n.validators.Load().(keys.PublicKeys); vals != nil && numOfCNs == len(vals) {
 		return vals.Copy(), nil
 	}
 	result, _, err := n.computeCommitteeMembers(bc, d)
 	if err != nil {
 		return nil, err
 	}
-	result = result[:bc.GetConfig().ValidatorsCount]
+	result = result[:numOfCNs]
 	sort.Sort(result)
 	n.validators.Store(result)
 	return result, nil
@@ -1007,7 +1011,9 @@ func (n *NEO) computeCommitteeMembers(bc interop.Ledger, d dao.DAO) (keys.Public
 	voterTurnout := votersCount.Div(votersCount, totalSupply)
 
 	sbVals := bc.GetStandByCommittee()
-	count := len(sbVals)
+	cfg := bc.GetConfig()
+	count := cfg.GetCommitteeSize(bc.BlockHeight() + 1)
+	sbVals = sbVals[:count]
 	cs, err := n.getCandidates(d, false)
 	if err != nil {
 		return nil, nil, err

pkg/core/native/notary.go

@@ -392,9 +392,10 @@ func (n *Notary) GetMaxNotValidBeforeDelta(dao dao.DAO) uint32 {
 // setMaxNotValidBeforeDelta is Notary contract method and sets the maximum NotValidBefore delta.
 func (n *Notary) setMaxNotValidBeforeDelta(ic *interop.Context, args []stackitem.Item) stackitem.Item {
 	value := toUint32(args[0])
-	maxInc := ic.Chain.GetConfig().MaxValidUntilBlockIncrement
+	cfg := ic.Chain.GetConfig()
-	if value > maxInc/2 || value < uint32(ic.Chain.GetConfig().ValidatorsCount) {
+	maxInc := cfg.MaxValidUntilBlockIncrement
-		panic(fmt.Errorf("MaxNotValidBeforeDelta cannot be more than %d or less than %d", maxInc/2, ic.Chain.GetConfig().ValidatorsCount))
+	if value > maxInc/2 || value < uint32(cfg.GetNumOfCNs(ic.Chain.BlockHeight())) {
+		panic(fmt.Errorf("MaxNotValidBeforeDelta cannot be more than %d or less than %d", maxInc/2, cfg.GetNumOfCNs(ic.Chain.BlockHeight())))
 	}
 	if !n.NEO.checkCommittee(ic) {
 		panic("invalid committee signature")

pkg/core/util.go

@@ -53,7 +53,7 @@ func validatorsFromConfig(cfg config.ProtocolConfiguration) ([]*keys.PublicKey,
 	if err != nil {
 		return nil, err
 	}
-	return vs[:cfg.ValidatorsCount], nil
+	return vs[:cfg.GetNumOfCNs(0)], nil
 }
 
 func committeeFromConfig(cfg config.ProtocolConfiguration) ([]*keys.PublicKey, error) {

pkg/network/server.go

@@ -1393,8 +1393,10 @@ func (s *Server) broadcastTxHashes(hs []util.Uint256) {
 // initStaleMemPools initializes mempools for stale tx/payload processing.
 func (s *Server) initStaleMemPools() {
 	threshold := 5
-	if s.config.ValidatorsCount*2 > threshold {
+	// Not perfect, can change over time, but should be sufficient.
-		threshold = s.config.ValidatorsCount * 2
+	numOfCNs := s.config.GetNumOfCNs(s.chain.BlockHeight())
+	if numOfCNs*2 > threshold {
+		threshold = numOfCNs * 2
 	}
 
 	s.mempool.SetResendThreshold(uint32(threshold), s.broadcastTX)

pkg/rpc/server/server.go

@@ -533,7 +533,7 @@ func (s *Server) getVersion(_ request.Params) (interface{}, *response.Error) {
 			MaxValidUntilBlockIncrement: cfg.MaxValidUntilBlockIncrement,
 			MaxTransactionsPerBlock:     cfg.MaxTransactionsPerBlock,
 			MemoryPoolMaxTransactions:   cfg.MemPoolSize,
-			ValidatorsCount:             byte(cfg.ValidatorsCount),
+			ValidatorsCount:             byte(cfg.GetNumOfCNs(s.chain.BlockHeight())),
 			InitialGasDistribution:      cfg.InitialGASSupply,
 			StateRootInHeader:           cfg.StateRootInHeader,
 		},