native: do not update committee every block

Update frequency depends on committee size and
amount of validators. For mainnet it is 28.

pkg/core/native/native_neo.go

@@ -31,7 +31,8 @@ type NEO struct {
 	nextValidators atomic.Value
 	validators     atomic.Value
 	// committee contains cached committee members and
-	// is updated during block persist. It's value
+	// is updated once in a while depending on committee size
+	// (every 28 blocks for mainnet). It's value
 	// is always equal to value stored by `prefixCommittee`.
 	committee atomic.Value
 }
@@ -212,10 +213,18 @@ func (n *NEO) updateCommittee(ic *interop.Context) error {
 	return ic.DAO.PutStorageItem(n.ContractID, prefixCommittee, si)
 }
 
+func shouldUpdateCommittee(h uint32, bc blockchainer.Blockchainer) bool {
+	cfg := bc.GetConfig()
+	r := cfg.ValidatorsCount + len(cfg.StandbyCommittee)
+	return h%uint32(r) == 0
+}
+
 // OnPersist implements Contract interface.
 func (n *NEO) OnPersist(ic *interop.Context) error {
-	if err := n.updateCommittee(ic); err != nil {
+	if shouldUpdateCommittee(ic.Block.Index, ic.Chain) {
-		return err
+		if err := n.updateCommittee(ic); err != nil {
+			return err
+		}
 	}
 
 	gas, err := n.GetGASPerBlock(ic, ic.Block.Index)

pkg/core/native_neo_test.go

@@ -35,6 +35,14 @@ func TestNEO_Vote(t *testing.T) {
 	ic.VM = vm.New()
 	ic.Block = bc.newBlock(tx)
 
+	freq := testchain.ValidatorsCount + testchain.CommitteeSize()
+	advanceChain := func(t *testing.T) {
+		for i := 0; i < freq; i++ {
+			require.NoError(t, neo.OnPersist(ic))
+			ic.Block.Index++
+		}
+	}
+
 	standBySorted := bc.GetStandByValidators()
 	sort.Sort(standBySorted)
 	pubs, err := neo.ComputeNextBlockValidators(bc, ic.DAO)
@@ -73,7 +81,7 @@ func TestNEO_Vote(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, standBySorted, pubs)
 
-	require.NoError(t, neo.OnPersist(ic))
+	advanceChain(t)
 	pubs = neo.GetNextBlockValidatorsInternal()
 	require.EqualValues(t, standBySorted, pubs)
 
@@ -90,7 +98,7 @@ func TestNEO_Vote(t *testing.T) {
 		require.NoError(t, neo.RegisterCandidateInternal(ic, priv.PublicKey()))
 	}
 
-	require.NoError(t, neo.OnPersist(ic))
+	advanceChain(t)
 	pubs, err = neo.ComputeNextBlockValidators(bc, ic.DAO)
 	require.NoError(t, err)
 	sortedCandidates := candidates.Copy()
@@ -102,7 +110,7 @@ func TestNEO_Vote(t *testing.T) {
 
 	require.NoError(t, neo.UnregisterCandidateInternal(ic, candidates[0]))
 	require.Error(t, neo.VoteInternal(ic, h, candidates[0]))
-	require.NoError(t, neo.OnPersist(ic))
+	advanceChain(t)
 
 	pubs, err = neo.ComputeNextBlockValidators(bc, ic.DAO)
 	require.NoError(t, err)