Merge pull request #21047 from holiman/improve_updates_2

core: improve trie updates (part 2)

accounts/abi/bind/backends/simulated.go

@@ -125,10 +125,9 @@ func (b *SimulatedBackend) Rollback() {
 
 func (b *SimulatedBackend) rollback() {
 	blocks, _ := core.GenerateChain(b.config, b.blockchain.CurrentBlock(), ethash.NewFaker(), b.database, 1, func(int, *core.BlockGen) {})
-	stateDB, _ := b.blockchain.State()
 
 	b.pendingBlock = blocks[0]
-	b.pendingState, _ = state.New(b.pendingBlock.Root(), stateDB.Database(), nil)
+	b.pendingState, _ = state.New(b.pendingBlock.Root(), b.blockchain.StateCache(), nil)
 }
 
 // stateByBlockNumber retrieves a state by a given blocknumber.

core/blockchain.go

@@ -203,7 +203,7 @@ type BlockChain struct {
 
 	engine     consensus.Engine
 	validator  Validator // Block and state validator interface
-	prefetcher Prefetcher // Block state prefetcher interface
+	prefetcher Prefetcher
 	processor  Processor // Block transaction processor interface
 	vmConfig   vm.Config
 
@@ -1860,12 +1860,17 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, er
 		if err != nil {
 			return it.index, err
 		}
+		// Enable prefetching to pull in trie node paths while processing transactions
+		statedb.StartPrefetcher("chain")
+		defer statedb.StopPrefetcher() // stopped on write anyway, defer meant to catch early error returns
+
 		// If we have a followup block, run that against the current state to pre-cache
 		// transactions and probabilistically some of the account/storage trie nodes.
 		var followupInterrupt uint32
 		if !bc.cacheConfig.TrieCleanNoPrefetch {
 			if followup, err := it.peek(); followup != nil && err == nil {
 				throwaway, _ := state.New(parent.Root, bc.stateCache, bc.snaps)
+
 				go func(start time.Time, followup *types.Block, throwaway *state.StateDB, interrupt *uint32) {
 					bc.prefetcher.Prefetch(followup, throwaway, bc.vmConfig, &followupInterrupt)
 
@@ -1891,7 +1896,6 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, er
 		storageUpdateTimer.Update(statedb.StorageUpdates)             // Storage updates are complete, we can mark them
 		snapshotAccountReadTimer.Update(statedb.SnapshotAccountReads) // Account reads are complete, we can mark them
 		snapshotStorageReadTimer.Update(statedb.SnapshotStorageReads) // Storage reads are complete, we can mark them
-
 		triehash := statedb.AccountHashes + statedb.StorageHashes     // Save to not double count in validation
 		trieproc := statedb.SnapshotAccountReads + statedb.AccountReads + statedb.AccountUpdates
 		trieproc += statedb.SnapshotStorageReads + statedb.StorageReads + statedb.StorageUpdates
@@ -1920,7 +1924,6 @@ func (bc *BlockChain) insertChain(chain types.Blocks, verifySeals bool) (int, er
 		if err != nil {
 			return it.index, err
 		}
-
 		// Update the metrics touched during block commit
 		accountCommitTimer.Update(statedb.AccountCommits)   // Account commits are complete, we can mark them
 		storageCommitTimer.Update(statedb.StorageCommits)   // Storage commits are complete, we can mark them

core/state/database.go

@@ -129,12 +129,20 @@ type cachingDB struct {
 
 // OpenTrie opens the main account trie at a specific root hash.
 func (db *cachingDB) OpenTrie(root common.Hash) (Trie, error) {
-	return trie.NewSecure(root, db.db)
+	tr, err := trie.NewSecure(root, db.db)
+	if err != nil {
+		return nil, err
+	}
+	return tr, nil
 }
 
 // OpenStorageTrie opens the storage trie of an account.
 func (db *cachingDB) OpenStorageTrie(addrHash, root common.Hash) (Trie, error) {
-	return trie.NewSecure(root, db.db)
+	tr, err := trie.NewSecure(root, db.db)
+	if err != nil {
+		return nil, err
+	}
+	return tr, nil
 }
 
 // CopyTrie returns an independent copy of the given trie.

core/state/state_object.go

@@ -156,6 +156,14 @@ func (s *stateObject) touch() {
 }
 
 func (s *stateObject) getTrie(db Database) Trie {
+	if s.trie == nil {
+		// Try fetching from prefetcher first
+		// We don't prefetch empty tries
+		if s.data.Root != emptyRoot && s.db.prefetcher != nil {
+			// When the miner is creating the pending state, there is no
+			// prefetcher
+			s.trie = s.db.prefetcher.trie(s.data.Root)
+		}
 		if s.trie == nil {
 			var err error
 			s.trie, err = db.OpenStorageTrie(s.addrHash, s.data.Root)
@@ -164,6 +172,7 @@ func (s *stateObject) getTrie(db Database) Trie {
 				s.setError(fmt.Errorf("can't create storage trie: %v", err))
 			}
 		}
+	}
 	return s.trie
 }
 
@@ -199,10 +208,22 @@ func (s *stateObject) GetCommittedState(db Database, key common.Hash) common.Has
 	var (
 		enc   []byte
 		err   error
+		meter *time.Duration
 	)
+	readStart := time.Now()
+	if metrics.EnabledExpensive {
+		// If the snap is 'under construction', the first lookup may fail. If that
+		// happens, we don't want to double-count the time elapsed. Thus this
+		// dance with the metering.
+		defer func() {
+			if meter != nil {
+				*meter += time.Since(readStart)
+			}
+		}()
+	}
 	if s.db.snap != nil {
 		if metrics.EnabledExpensive {
-			defer func(start time.Time) { s.db.SnapshotStorageReads += time.Since(start) }(time.Now())
+			meter = &s.db.SnapshotStorageReads
 		}
 		// If the object was destructed in *this* block (and potentially resurrected),
 		// the storage has been cleared out, and we should *not* consult the previous
@@ -217,8 +238,14 @@ func (s *stateObject) GetCommittedState(db Database, key common.Hash) common.Has
 	}
 	// If snapshot unavailable or reading from it failed, load from the database
 	if s.db.snap == nil || err != nil {
+		if meter != nil {
+			// If we already spent time checking the snapshot, account for it
+			// and reset the readStart
+			*meter += time.Since(readStart)
+			readStart = time.Now()
+		}
 		if metrics.EnabledExpensive {
-			defer func(start time.Time) { s.db.StorageReads += time.Since(start) }(time.Now())
+			meter = &s.db.StorageReads
 		}
 		if enc, err = s.getTrie(db).TryGet(key.Bytes()); err != nil {
 			s.setError(err)
@@ -282,9 +309,16 @@ func (s *stateObject) setState(key, value common.Hash) {
 
 // finalise moves all dirty storage slots into the pending area to be hashed or
 // committed later. It is invoked at the end of every transaction.
-func (s *stateObject) finalise() {
+func (s *stateObject) finalise(prefetch bool) {
+	slotsToPrefetch := make([][]byte, 0, len(s.dirtyStorage))
 	for key, value := range s.dirtyStorage {
 		s.pendingStorage[key] = value
+		if value != s.originStorage[key] {
+			slotsToPrefetch = append(slotsToPrefetch, common.CopyBytes(key[:])) // Copy needed for closure
+		}
+	}
+	if s.db.prefetcher != nil && prefetch && len(slotsToPrefetch) > 0 && s.data.Root != emptyRoot {
+		s.db.prefetcher.prefetch(s.data.Root, slotsToPrefetch)
 	}
 	if len(s.dirtyStorage) > 0 {
 		s.dirtyStorage = make(Storage)
@@ -295,7 +329,7 @@ func (s *stateObject) finalise() {
 // It will return nil if the trie has not been loaded and no changes have been made
 func (s *stateObject) updateTrie(db Database) Trie {
 	// Make sure all dirty slots are finalized into the pending storage area
-	s.finalise()
+	s.finalise(false) // Don't prefetch any more, pull directly if need be
 	if len(s.pendingStorage) == 0 {
 		return s.trie
 	}
@@ -303,18 +337,13 @@ func (s *stateObject) updateTrie(db Database) Trie {
 	if metrics.EnabledExpensive {
 		defer func(start time.Time) { s.db.StorageUpdates += time.Since(start) }(time.Now())
 	}
-	// Retrieve the snapshot storage map for the object
+	// The snapshot storage map for the object
 	var storage map[common.Hash][]byte
-	if s.db.snap != nil {
-		// Retrieve the old storage map, if available, create a new one otherwise
-		storage = s.db.snapStorage[s.addrHash]
-		if storage == nil {
-			storage = make(map[common.Hash][]byte)
-			s.db.snapStorage[s.addrHash] = storage
-		}
-	}
 	// Insert all the pending updates into the trie
 	tr := s.getTrie(db)
+	hasher := s.db.hasher
+
+	usedStorage := make([][]byte, 0, len(s.pendingStorage))
 	for key, value := range s.pendingStorage {
 		// Skip noop changes, persist actual changes
 		if value == s.originStorage[key] {
@@ -331,9 +360,20 @@ func (s *stateObject) updateTrie(db Database) Trie {
 			s.setError(tr.TryUpdate(key[:], v))
 		}
 		// If state snapshotting is active, cache the data til commit
-		if storage != nil {
-			storage[crypto.Keccak256Hash(key[:])] = v // v will be nil if value is 0x00
+		if s.db.snap != nil {
+			if storage == nil {
+				// Retrieve the old storage map, if available, create a new one otherwise
+				if storage = s.db.snapStorage[s.addrHash]; storage == nil {
+					storage = make(map[common.Hash][]byte)
+					s.db.snapStorage[s.addrHash] = storage
+				}
+			}
+			storage[crypto.HashData(hasher, key[:])] = v // v will be nil if value is 0x00
+		}
+		usedStorage = append(usedStorage, common.CopyBytes(key[:])) // Copy needed for closure
 	}
+	if s.db.prefetcher != nil {
+		s.db.prefetcher.used(s.data.Root, usedStorage)
 	}
 	if len(s.pendingStorage) > 0 {
 		s.pendingStorage = make(Storage)

core/state/state_test.go

@@ -170,7 +170,7 @@ func TestSnapshot2(t *testing.T) {
 	state.setStateObject(so0)
 
 	root, _ := state.Commit(false)
-	state.Reset(root)
+	state, _ = New(root, state.db, state.snaps)
 
 	// and one with deleted == true
 	so1 := state.getStateObject(stateobjaddr1)

core/state/statedb.go

@@ -63,7 +63,10 @@ func (n *proofList) Delete(key []byte) error {
 // * Accounts
 type StateDB struct {
 	db           Database
+	prefetcher   *triePrefetcher
+	originalRoot common.Hash // The pre-state root, before any changes were made
 	trie         Trie
+	hasher       crypto.KeccakState
 
 	snaps         *snapshot.Tree
 	snap          snapshot.Snapshot
@@ -125,6 +128,7 @@ func New(root common.Hash, db Database, snaps *snapshot.Tree) (*StateDB, error)
 	sdb := &StateDB{
 		db:                  db,
 		trie:                tr,
+		originalRoot:        root,
 		snaps:               snaps,
 		stateObjects:        make(map[common.Address]*stateObject),
 		stateObjectsPending: make(map[common.Address]struct{}),
@@ -133,6 +137,7 @@ func New(root common.Hash, db Database, snaps *snapshot.Tree) (*StateDB, error)
 		preimages:           make(map[common.Hash][]byte),
 		journal:             newJournal(),
 		accessList:          newAccessList(),
+		hasher:              crypto.NewKeccakState(),
 	}
 	if sdb.snaps != nil {
 		if sdb.snap = sdb.snaps.Snapshot(root); sdb.snap != nil {
@@ -144,6 +149,28 @@ func New(root common.Hash, db Database, snaps *snapshot.Tree) (*StateDB, error)
 	return sdb, nil
 }
 
+// StartPrefetcher initializes a new trie prefetcher to pull in nodes from the
+// state trie concurrently while the state is mutated so that when we reach the
+// commit phase, most of the needed data is already hot.
+func (s *StateDB) StartPrefetcher(namespace string) {
+	if s.prefetcher != nil {
+		s.prefetcher.close()
+		s.prefetcher = nil
+	}
+	if s.snap != nil {
+		s.prefetcher = newTriePrefetcher(s.db, s.originalRoot, namespace)
+	}
+}
+
+// StopPrefetcher terminates a running prefetcher and reports any leftover stats
+// from the gathered metrics.
+func (s *StateDB) StopPrefetcher() {
+	if s.prefetcher != nil {
+		s.prefetcher.close()
+		s.prefetcher = nil
+	}
+}
+
 // setError remembers the first non-nil error it is called with.
 func (s *StateDB) setError(err error) {
 	if s.dbErr == nil {
@@ -155,37 +182,6 @@ func (s *StateDB) Error() error {
 	return s.dbErr
 }
 
-// Reset clears out all ephemeral state objects from the state db, but keeps
-// the underlying state trie to avoid reloading data for the next operations.
-func (s *StateDB) Reset(root common.Hash) error {
-	tr, err := s.db.OpenTrie(root)
-	if err != nil {
-		return err
-	}
-	s.trie = tr
-	s.stateObjects = make(map[common.Address]*stateObject)
-	s.stateObjectsPending = make(map[common.Address]struct{})
-	s.stateObjectsDirty = make(map[common.Address]struct{})
-	s.thash = common.Hash{}
-	s.bhash = common.Hash{}
-	s.txIndex = 0
-	s.logs = make(map[common.Hash][]*types.Log)
-	s.logSize = 0
-	s.preimages = make(map[common.Hash][]byte)
-	s.clearJournalAndRefund()
-
-	if s.snaps != nil {
-		s.snapAccounts, s.snapDestructs, s.snapStorage = nil, nil, nil
-		if s.snap = s.snaps.Snapshot(root); s.snap != nil {
-			s.snapDestructs = make(map[common.Hash]struct{})
-			s.snapAccounts = make(map[common.Hash][]byte)
-			s.snapStorage = make(map[common.Hash]map[common.Hash][]byte)
-		}
-	}
-	s.accessList = newAccessList()
-	return nil
-}
-
 func (s *StateDB) AddLog(log *types.Log) {
 	s.journal.append(addLogChange{txhash: s.thash})
 
@@ -532,7 +528,7 @@ func (s *StateDB) getDeletedStateObject(addr common.Address) *stateObject {
 			defer func(start time.Time) { s.SnapshotAccountReads += time.Since(start) }(time.Now())
 		}
 		var acc *snapshot.Account
-		if acc, err = s.snap.Account(crypto.Keccak256Hash(addr.Bytes())); err == nil {
+		if acc, err = s.snap.Account(crypto.HashData(s.hasher, addr.Bytes())); err == nil {
 			if acc == nil {
 				return nil
 			}
@@ -675,6 +671,7 @@ func (s *StateDB) Copy() *StateDB {
 		logSize:             s.logSize,
 		preimages:           make(map[common.Hash][]byte, len(s.preimages)),
 		journal:             newJournal(),
+		hasher:              crypto.NewKeccakState(),
 	}
 	// Copy the dirty states, logs, and preimages
 	for addr := range s.journal.dirties {
@@ -724,6 +721,13 @@ func (s *StateDB) Copy() *StateDB {
 	// However, it doesn't cost us much to copy an empty list, so we do it anyway
 	// to not blow up if we ever decide copy it in the middle of a transaction
 	state.accessList = s.accessList.Copy()
+
+	// If there's a prefetcher running, make an inactive copy of it that can
+	// only access data but does not actively preload (since the user will not
+	// know that they need to explicitly terminate an active copy).
+	if s.prefetcher != nil {
+		state.prefetcher = s.prefetcher.copy()
+	}
 	return state
 }
 
@@ -760,6 +764,7 @@ func (s *StateDB) GetRefund() uint64 {
 // the journal as well as the refunds. Finalise, however, will not push any updates
 // into the tries just yet. Only IntermediateRoot or Commit will do that.
 func (s *StateDB) Finalise(deleteEmptyObjects bool) {
+	addressesToPrefetch := make([][]byte, 0, len(s.journal.dirties))
 	for addr := range s.journal.dirties {
 		obj, exist := s.stateObjects[addr]
 		if !exist {
@@ -784,10 +789,18 @@ func (s *StateDB) Finalise(deleteEmptyObjects bool) {
 				delete(s.snapStorage, obj.addrHash)        // Clear out any previously updated storage data (may be recreated via a ressurrect)
 			}
 		} else {
-			obj.finalise()
+			obj.finalise(true) // Prefetch slots in the background
 		}
 		s.stateObjectsPending[addr] = struct{}{}
 		s.stateObjectsDirty[addr] = struct{}{}
+
+		// At this point, also ship the address off to the precacher. The precacher
+		// will start loading tries, and when the change is eventually committed,
+		// the commit-phase will be a lot faster
+		addressesToPrefetch = append(addressesToPrefetch, common.CopyBytes(addr[:])) // Copy needed for closure
+	}
+	if s.prefetcher != nil && len(addressesToPrefetch) > 0 {
+		s.prefetcher.prefetch(s.originalRoot, addressesToPrefetch)
 	}
 	// Invalidate journal because reverting across transactions is not allowed.
 	s.clearJournalAndRefund()
@@ -800,14 +813,49 @@ func (s *StateDB) IntermediateRoot(deleteEmptyObjects bool) common.Hash {
 	// Finalise all the dirty storage states and write them into the tries
 	s.Finalise(deleteEmptyObjects)
 
+	// If there was a trie prefetcher operating, it gets aborted and irrevocably
+	// modified after we start retrieving tries. Remove it from the statedb after
+	// this round of use.
+	//
+	// This is weird pre-byzantium since the first tx runs with a prefetcher and
+	// the remainder without, but pre-byzantium even the initial prefetcher is
+	// useless, so no sleep lost.
+	prefetcher := s.prefetcher
+	if s.prefetcher != nil {
+		defer func() {
+			s.prefetcher.close()
+			s.prefetcher = nil
+		}()
+	}
+	// Although naively it makes sense to retrieve the account trie and then do
+	// the contract storage and account updates sequentially, that short circuits
+	// the account prefetcher. Instead, let's process all the storage updates
+	// first, giving the account prefeches just a few more milliseconds of time
+	// to pull useful data from disk.
 	for addr := range s.stateObjectsPending {
-		obj := s.stateObjects[addr]
-		if obj.deleted {
+		if obj := s.stateObjects[addr]; !obj.deleted {
+			obj.updateRoot(s.db)
+		}
+	}
+	// Now we're about to start to write changes to the trie. The trie is so far
+	// _untouched_. We can check with the prefetcher, if it can give us a trie
+	// which has the same root, but also has some content loaded into it.
+	if prefetcher != nil {
+		if trie := prefetcher.trie(s.originalRoot); trie != nil {
+			s.trie = trie
+		}
+	}
+	usedAddrs := make([][]byte, 0, len(s.stateObjectsPending))
+	for addr := range s.stateObjectsPending {
+		if obj := s.stateObjects[addr]; obj.deleted {
 			s.deleteStateObject(obj)
 		} else {
-			obj.updateRoot(s.db)
 			s.updateStateObject(obj)
 		}
+		usedAddrs = append(usedAddrs, common.CopyBytes(addr[:])) // Copy needed for closure
+	}
+	if prefetcher != nil {
+		prefetcher.used(s.originalRoot, usedAddrs)
 	}
 	if len(s.stateObjectsPending) > 0 {
 		s.stateObjectsPending = make(map[common.Address]struct{})

core/state/statedb_test.go

@@ -474,7 +474,7 @@ func TestTouchDelete(t *testing.T) {
 	s := newStateTest()
 	s.state.GetOrNewStateObject(common.Address{})
 	root, _ := s.state.Commit(false)
-	s.state.Reset(root)
+	s.state, _ = New(root, s.state.db, s.state.snaps)
 
 	snapshot := s.state.Snapshot()
 	s.state.AddBalance(common.Address{}, new(big.Int))
@@ -676,7 +676,7 @@ func TestDeleteCreateRevert(t *testing.T) {
 	state.SetBalance(addr, big.NewInt(1))
 
 	root, _ := state.Commit(false)
-	state.Reset(root)
+	state, _ = New(root, state.db, state.snaps)
 
 	// Simulate self-destructing in one transaction, then create-reverting in another
 	state.Suicide(addr)
@@ -688,7 +688,7 @@ func TestDeleteCreateRevert(t *testing.T) {
 
 	// Commit the entire state and make sure we don't crash and have the correct state
 	root, _ = state.Commit(true)
-	state.Reset(root)
+	state, _ = New(root, state.db, state.snaps)
 
 	if state.getStateObject(addr) != nil {
 		t.Fatalf("self-destructed contract came alive")

crypto/crypto.go

@@ -60,10 +60,23 @@ type KeccakState interface {
 	Read([]byte) (int, error)
 }
 
+// NewKeccakState creates a new KeccakState
+func NewKeccakState() KeccakState {
+	return sha3.NewLegacyKeccak256().(KeccakState)
+}
+
+// HashData hashes the provided data using the KeccakState and returns a 32 byte hash
+func HashData(kh KeccakState, data []byte) (h common.Hash) {
+	kh.Reset()
+	kh.Write(data)
+	kh.Read(h[:])
+	return h
+}
+
 // Keccak256 calculates and returns the Keccak256 hash of the input data.
 func Keccak256(data ...[]byte) []byte {
 	b := make([]byte, 32)
-	d := sha3.NewLegacyKeccak256().(KeccakState)
+	d := NewKeccakState()
 	for _, b := range data {
 		d.Write(b)
 	}
@@ -74,7 +87,7 @@ func Keccak256(data ...[]byte) []byte {
 // Keccak256Hash calculates and returns the Keccak256 hash of the input data,
 // converting it to an internal Hash data structure.
 func Keccak256Hash(data ...[]byte) (h common.Hash) {
-	d := sha3.NewLegacyKeccak256().(KeccakState)
+	d := NewKeccakState()
 	for _, b := range data {
 		d.Write(b)
 	}

crypto/crypto_test.go

@@ -42,6 +42,13 @@ func TestKeccak256Hash(t *testing.T) {
 	checkhash(t, "Sha3-256-array", func(in []byte) []byte { h := Keccak256Hash(in); return h[:] }, msg, exp)
 }
 
+func TestKeccak256Hasher(t *testing.T) {
+	msg := []byte("abc")
+	exp, _ := hex.DecodeString("4e03657aea45a94fc7d47ba826c8d667c0d1e6e33a64a036ec44f58fa12d6c45")
+	hasher := NewKeccakState()
+	checkhash(t, "Sha3-256-array", func(in []byte) []byte { h := HashData(hasher, in); return h[:] }, msg, exp)
+}
+
 func TestToECDSAErrors(t *testing.T) {
 	if _, err := HexToECDSA("0000000000000000000000000000000000000000000000000000000000000000"); err == nil {
 		t.Fatal("HexToECDSA should've returned error")

eth/api_tracer.go

@@ -299,7 +299,8 @@ func (api *PrivateDebugAPI) traceChain(ctx context.Context, start, end *types.Bl
 				failed = err
 				break
 			}
-			if err := statedb.Reset(root); err != nil {
+			statedb, err = state.New(root, database, nil)
+			if err != nil {
 				failed = err
 				break
 			}
@@ -699,7 +700,8 @@ func (api *PrivateDebugAPI) computeStateDB(block *types.Block, reexec uint64) (*
 		if err != nil {
 			return nil, err
 		}
-		if err := statedb.Reset(root); err != nil {
+		statedb, err = state.New(root, database, nil)
+		if err != nil {
 			return nil, fmt.Errorf("state reset after block %d failed: %v", block.NumberU64(), err)
 		}
 		database.TrieDB().Reference(root, common.Hash{})

miner/worker.go

@@ -303,6 +303,9 @@ func (w *worker) isRunning() bool {
 // close terminates all background threads maintained by the worker.
 // Note the worker does not support being closed multiple times.
 func (w *worker) close() {
+	if w.current != nil && w.current.state != nil {
+		w.current.state.StopPrefetcher()
+	}
 	atomic.StoreInt32(&w.running, 0)
 	close(w.exitCh)
 }
@@ -642,10 +645,14 @@ func (w *worker) resultLoop() {
 
 // makeCurrent creates a new environment for the current cycle.
 func (w *worker) makeCurrent(parent *types.Block, header *types.Header) error {
+	// Retrieve the parent state to execute on top and start a prefetcher for
+	// the miner to speed block sealing up a bit
 	state, err := w.chain.StateAt(parent.Root())
 	if err != nil {
 		return err
 	}
+	state.StartPrefetcher("miner")
+
 	env := &environment{
 		signer:    types.NewEIP155Signer(w.chainConfig.ChainID),
 		state:     state,
@@ -654,7 +661,6 @@ func (w *worker) makeCurrent(parent *types.Block, header *types.Header) error {
 		uncles:    mapset.NewSet(),
 		header:    header,
 	}
-
 	// when 08 is processed ancestors contain 07 (quick block)
 	for _, ancestor := range w.chain.GetBlocksFromHash(parent.Hash(), 7) {
 		for _, uncle := range ancestor.Uncles() {
@@ -663,9 +669,14 @@ func (w *worker) makeCurrent(parent *types.Block, header *types.Header) error {
 		env.family.Add(ancestor.Hash())
 		env.ancestors.Add(ancestor.Hash())
 	}
-
 	// Keep track of transactions which return errors so they can be removed
 	env.tcount = 0
+
+	// Swap out the old work with the new one, terminating any leftover prefetcher
+	// processes in the mean time and starting a new one.
+	if w.current != nil && w.current.state != nil {
+		w.current.state.StopPrefetcher()
+	}
 	w.current = env
 	return nil
 }
@@ -719,7 +730,6 @@ func (w *worker) updateSnapshot() {
 		w.current.receipts,
 		new(trie.Trie),
 	)
-
 	w.snapshotState = w.current.state.Copy()
 }