consensus: try to use previous proposal after ChangeView

When system and network pressure is high it can be beneficial
to use transactions which and were already proposed.
The assumption is that they will be in other node's memory pool
with more probability.

pkg/consensus/consensus.go

@@ -55,6 +55,7 @@ type service struct {
 	// everything in single thread.
 	messages     chan Payload
 	transactions chan *transaction.Transaction
+	lastProposal []util.Uint256
 }
 
 // Config is a configuration for consensus services.
@@ -205,7 +206,9 @@ func (s *service) OnPayload(cp *Payload) {
 	// we use switch here because other payloads could be possibly added in future
 	switch cp.Type() {
 	case payload.PrepareRequestType:
-		s.txx.Add(&cp.GetPrepareRequest().(*prepareRequest).minerTx)
+		req := cp.GetPrepareRequest().(*prepareRequest)
+		s.txx.Add(&req.minerTx)
+		s.lastProposal = req.transactionHashes
 	}
 
 	s.messages <- *cp
@@ -328,7 +331,23 @@ func (s *service) getBlock(h util.Uint256) block.Block {
 
 func (s *service) getVerifiedTx(count int) []block.Transaction {
 	pool := s.Config.Chain.GetMemPool()
-	txx := pool.GetVerifiedTransactions()
+
+	var txx []*transaction.Transaction
+
+	if s.dbft.ViewNumber > 0 {
+		txx = make([]*transaction.Transaction, 0, len(s.lastProposal))
+		for i := range s.lastProposal {
+			if tx, ok := pool.TryGetValue(s.lastProposal[i]); ok {
+				txx = append(txx, tx)
+			}
+		}
+
+		if len(txx) < len(s.lastProposal)/2 {
+			txx = pool.GetVerifiedTransactions()
+		}
+	} else {
+		txx = pool.GetVerifiedTransactions()
+	}
 
 	res := make([]block.Transaction, len(txx)+1)
 	for i := range txx {

pkg/consensus/consensus_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/CityOfZion/neo-go/pkg/core/transaction"
 	"github.com/CityOfZion/neo-go/pkg/util"
 	"github.com/nspcc-dev/dbft/block"
+	"github.com/nspcc-dev/dbft/payload"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/zap/zaptest"
 )
@@ -28,6 +29,53 @@ func TestNewService(t *testing.T) {
 	require.Equal(t, tx, txx[1])
 }
 
+func TestService_GetVerified(t *testing.T) {
+	srv := newTestService(t)
+	txs := []*transaction.Transaction{
+		newMinerTx(1),
+		newMinerTx(2),
+		newMinerTx(3),
+		newMinerTx(4),
+	}
+	pool := srv.Chain.GetMemPool()
+	item := core.NewPoolItem(txs[3], new(feer))
+
+	require.True(t, pool.TryAdd(txs[3].Hash(), item))
+
+	hashes := []util.Uint256{txs[0].Hash(), txs[1].Hash(), txs[2].Hash()}
+
+	p := new(Payload)
+	p.SetType(payload.PrepareRequestType)
+	p.SetPayload(&prepareRequest{transactionHashes: hashes})
+	p.SetValidatorIndex(1)
+
+	priv, _ := getTestValidator(1)
+	require.NoError(t, p.Sign(priv))
+
+	srv.OnPayload(p)
+	require.Equal(t, hashes, srv.lastProposal)
+
+	srv.dbft.ViewNumber = 1
+
+	t.Run("new transactions will be proposed in case of failure", func(t *testing.T) {
+		txx := srv.getVerifiedTx(10)
+		require.Equal(t, 2, len(txx), "there is only 1 tx in mempool")
+		require.Equal(t, txs[3], txx[1])
+	})
+
+	t.Run("more than half of the last proposal will be reused", func(t *testing.T) {
+		for _, tx := range txs[:2] {
+			item := core.NewPoolItem(tx, new(feer))
+			require.True(t, pool.TryAdd(tx.Hash(), item))
+		}
+
+		txx := srv.getVerifiedTx(10)
+		require.Contains(t, txx, txs[0])
+		require.Contains(t, txx, txs[1])
+		require.NotContains(t, txx, txs[2])
+	})
+}
+
 func TestService_ValidatePayload(t *testing.T) {
 	srv := newTestService(t)
 	priv, _ := getTestValidator(1)