cmd, core, eth, trie: track deleted nodes #22225 #25757 (#1120)

Co-authored-by: rjl493456442 <garyrong0905@gmail.com>
Co-authored-by: Martin Holst Swende <martin@swende.se>

XDCx/tradingstate/XDCx_trie.go

@@ -57,7 +57,7 @@ func NewXDCXTrie(root common.Hash, db *trie.Database) (*XDCXTrie, error) {
 	if db == nil {
 		panic("trie.NewXDCXTrie called without a database")
 	}
-	trie, err := trie.New(common.Hash{}, root, db)
+	trie, err := trie.New(trie.TrieID(root), db)
 	if err != nil {
 		return nil, err
 	}

XDCxlending/lendingstate/XDCx_trie.go

@@ -57,7 +57,7 @@ func NewXDCXTrie(root common.Hash, db *trie.Database) (*XDCXTrie, error) {
 	if db == nil {
 		panic("trie.NewXDCXTrie called without a database")
 	}
-	trie, err := trie.New(common.Hash{}, root, db)
+	trie, err := trie.New(trie.TrieID(root), db)
 	if err != nil {
 		return nil, err
 	}

cmd/XDC/dbcmd.go

@@ -21,6 +21,7 @@ import (
 	"os"
 	"path/filepath"
 	"slices"
+	"strconv"
 	"time"
 
 	"github.com/XinFinOrg/XDPoSChain/cmd/utils"
@@ -30,6 +31,7 @@ import (
 	"github.com/XinFinOrg/XDPoSChain/core/rawdb"
 	"github.com/XinFinOrg/XDPoSChain/ethdb"
 	"github.com/XinFinOrg/XDPoSChain/log"
+	"github.com/XinFinOrg/XDPoSChain/trie"
 	"github.com/urfave/cli/v2"
 )
 
@@ -54,6 +56,7 @@ Remove blockchain and state databases`,
 			dbGetCmd,
 			dbDeleteCmd,
 			dbPutCmd,
+			dbGetSlotsCmd,
 		},
 	}
 	dbInspectCmd = &cli.Command{
@@ -119,6 +122,16 @@ WARNING: This is a low-level operation which may cause database corruption!`,
 		Description: `This command sets a given database key to the given value.
 WARNING: This is a low-level operation which may cause database corruption!`,
 	}
+	dbGetSlotsCmd = &cli.Command{
+		Action:    dbDumpTrie,
+		Name:      "dumptrie",
+		Usage:     "Show the storage key/values of a given storage trie",
+		ArgsUsage: "<hex-encoded state root> <hex-encoded account hash> <hex-encoded storage trie root> <hex-encoded start (optional)> <int max elements (optional)>",
+		Flags: slices.Concat([]cli.Flag{
+			utils.SyncModeFlag,
+		}, utils.NetworkFlags, utils.DatabaseFlags),
+		Description: "This command looks up the specified database key from the database.",
+	}
 )
 
 func removeDB(ctx *cli.Context) error {
@@ -328,3 +341,64 @@ func dbPut(ctx *cli.Context) error {
 	}
 	return db.Put(key, value)
 }
+
+// dbDumpTrie shows the key-value slots of a given storage trie
+func dbDumpTrie(ctx *cli.Context) error {
+	if ctx.NArg() < 3 {
+		return fmt.Errorf("required arguments: %v", ctx.Command.ArgsUsage)
+	}
+	stack, _ := makeConfigNode(ctx)
+	defer stack.Close()
+
+	db := utils.MakeChainDatabase(ctx, stack, true)
+	defer db.Close()
+
+	var (
+		state   []byte
+		storage []byte
+		account []byte
+		start   []byte
+		max     = int64(-1)
+		err     error
+	)
+	if state, err = hexutil.Decode(ctx.Args().Get(0)); err != nil {
+		log.Info("Could not decode the state root", "error", err)
+		return err
+	}
+	if account, err = hexutil.Decode(ctx.Args().Get(1)); err != nil {
+		log.Info("Could not decode the account hash", "error", err)
+		return err
+	}
+	if storage, err = hexutil.Decode(ctx.Args().Get(2)); err != nil {
+		log.Info("Could not decode the storage trie root", "error", err)
+		return err
+	}
+	if ctx.NArg() > 3 {
+		if start, err = hexutil.Decode(ctx.Args().Get(3)); err != nil {
+			log.Info("Could not decode the seek position", "error", err)
+			return err
+		}
+	}
+	if ctx.NArg() > 4 {
+		if max, err = strconv.ParseInt(ctx.Args().Get(4), 10, 64); err != nil {
+			log.Info("Could not decode the max count", "error", err)
+			return err
+		}
+	}
+	id := trie.StorageTrieID(common.BytesToHash(state), common.BytesToHash(account), common.BytesToHash(storage))
+	theTrie, err := trie.New(id, trie.NewDatabase(db))
+	if err != nil {
+		return err
+	}
+	var count int64
+	it := trie.NewIterator(theTrie.NodeIterator(start))
+	for it.Next() {
+		if max > 0 && count == max {
+			fmt.Printf("Exiting after %d values\n", count)
+			break
+		}
+		fmt.Printf("  %d. key %#x: %#x\n", count, it.Key, it.Value)
+		count++
+	}
+	return it.Err
+}

core/blockchain.go

@@ -72,6 +72,8 @@ var (
 	storageUpdateTimer = metrics.NewRegisteredResettingTimer("chain/storage/updates", nil)
 	storageCommitTimer = metrics.NewRegisteredResettingTimer("chain/storage/commits", nil)
 
+	triedbCommitTimer = metrics.NewRegisteredTimer("chain/triedb/commits", nil)
+
 	blockInsertTimer     = metrics.NewRegisteredResettingTimer("chain/inserts", nil)
 	blockValidationTimer = metrics.NewRegisteredResettingTimer("chain/validation", nil)
 	blockExecutionTimer  = metrics.NewRegisteredResettingTimer("chain/execution", nil)
@@ -561,10 +563,10 @@ func (bc *BlockChain) FastSyncCommitHead(hash common.Hash) error {
 	if block == nil {
 		return fmt.Errorf("non existent block [%x..]", hash[:4])
 	}
-	if _, err := trie.NewStateTrie(common.Hash{}, block.Root(), bc.stateCache.TrieDB()); err != nil {
+	root := block.Root()
-		return err
+	if !bc.HasState(root) {
+		return fmt.Errorf("non existent state [%x..]", root[:4])
 	}
-
 	// If all checks out, manually set the head block.
 	if !bc.chainmu.TryLock() {
 		return errChainStopped
@@ -1932,6 +1934,7 @@ func (bc *BlockChain) processBlock(block *types.Block, parent *types.Header, sta
 	storageUpdateTimer.Update(statedb.StorageUpdates)                                 // Storage updates are complete(in validation)
 	accountHashTimer.Update(statedb.AccountHashes)                                    // Account hashes are complete(in validation)
 	storageHashTimer.Update(statedb.StorageHashes)                                    // Storage hashes are complete(in validation)
+	triedbCommitTimer.Update(statedb.TrieDBCommits)                                   // Triedb commits are complete, we can mark them
 	triehash := statedb.AccountHashes + statedb.StorageHashes                         // The time spent on tries hashing
 	trieUpdate := statedb.AccountUpdates + statedb.StorageUpdates                     // The time spent on tries update
 	blockExecutionTimer.Update(ptime - (statedb.AccountReads + statedb.StorageReads)) // The time spent on EVM processing

core/state/database.go

@@ -42,7 +42,7 @@ type Database interface {
 	OpenTrie(root common.Hash) (Trie, error)
 
 	// OpenStorageTrie opens the storage trie of an account.
-	OpenStorageTrie(addrHash, root common.Hash) (Trie, error)
+	OpenStorageTrie(stateRoot common.Hash, addrHash, root common.Hash) (Trie, error)
 
 	// CopyTrie returns an independent copy of the given trie.
 	CopyTrie(Trie) Trie
@@ -146,7 +146,7 @@ type cachingDB struct {
 
 // OpenTrie opens the main account trie at a specific root hash.
 func (db *cachingDB) OpenTrie(root common.Hash) (Trie, error) {
-	tr, err := trie.NewStateTrie(common.Hash{}, root, db.db)
+	tr, err := trie.NewStateTrie(trie.StateTrieID(root), db.db)
 	if err != nil {
 		return nil, err
 	}
@@ -154,8 +154,8 @@ func (db *cachingDB) OpenTrie(root common.Hash) (Trie, error) {
 }
 
 // OpenStorageTrie opens the storage trie of an account.
-func (db *cachingDB) OpenStorageTrie(addrHash, root common.Hash) (Trie, error) {
+func (db *cachingDB) OpenStorageTrie(stateRoot common.Hash, addrHash, root common.Hash) (Trie, error) {
-	tr, err := trie.NewStateTrie(addrHash, root, db.db)
+	tr, err := trie.NewStateTrie(trie.StorageTrieID(stateRoot, addrHash, root), db.db)
 	if err != nil {
 		return nil, err
 	}

core/state/iterator.go

@@ -109,7 +109,7 @@ func (it *nodeIterator) step() error {
 	if err := rlp.Decode(bytes.NewReader(it.stateIt.LeafBlob()), &account); err != nil {
 		return err
 	}
-	dataTrie, err := it.state.db.OpenStorageTrie(common.BytesToHash(it.stateIt.LeafKey()), account.Root)
+	dataTrie, err := it.state.db.OpenStorageTrie(it.state.originalRoot, common.BytesToHash(it.stateIt.LeafKey()), account.Root)
 	if err != nil {
 		return err
 	}

core/state/metrics.go

@@ -19,10 +19,12 @@ package state
 import "github.com/XinFinOrg/XDPoSChain/metrics"
 
 var (
-	accountUpdatedMeter        = metrics.NewRegisteredMeter("state/update/account", nil)
+	accountUpdatedMeter      = metrics.NewRegisteredMeter("state/update/account", nil)
-	storageUpdatedMeter        = metrics.NewRegisteredMeter("state/update/storage", nil)
+	storageUpdatedMeter      = metrics.NewRegisteredMeter("state/update/storage", nil)
-	accountDeletedMeter        = metrics.NewRegisteredMeter("state/delete/account", nil)
+	accountDeletedMeter      = metrics.NewRegisteredMeter("state/delete/account", nil)
-	storageDeletedMeter        = metrics.NewRegisteredMeter("state/delete/storage", nil)
+	storageDeletedMeter      = metrics.NewRegisteredMeter("state/delete/storage", nil)
-	accountTrieCommittedMeter  = metrics.NewRegisteredMeter("state/commit/accountnodes", nil)
+	accountTrieUpdatedMeter  = metrics.NewRegisteredMeter("state/update/accountnodes", nil)
-	storageTriesCommittedMeter = metrics.NewRegisteredMeter("state/commit/storagenodes", nil)
+	storageTriesUpdatedMeter = metrics.NewRegisteredMeter("state/update/storagenodes", nil)
+	accountTrieDeletedMeter  = metrics.NewRegisteredMeter("state/delete/accountnodes", nil)
+	storageTriesDeletedMeter = metrics.NewRegisteredMeter("state/delete/storagenodes", nil)
 )

core/state/state_object.go

@@ -158,7 +158,7 @@ func (s *stateObject) touch() {
 // be loaded.
 func (s *stateObject) getTrie(db Database) (Trie, error) {
 	if s.trie == nil {
-		tr, err := db.OpenStorageTrie(s.addrHash, s.data.Root)
+		tr, err := db.OpenStorageTrie(s.db.originalRoot, s.addrHash, s.data.Root)
 		if err != nil {
 			return nil, err
 		}

core/state/statedb.go

@@ -50,6 +50,10 @@ type StateDB struct {
 	trie   Trie
 	logger *tracing.Hooks
 
+	// originalRoot is the pre-state root, before any changes were made.
+	// It will be updated when the Commit is called.
+	originalRoot common.Hash
+
 	// This map holds 'live' objects, which will get modified while processing a state transition.
 	stateObjects         map[common.Address]*stateObject
 	stateObjectsPending  map[common.Address]struct{} // State objects finalized but not yet written to the trie
@@ -96,6 +100,7 @@ type StateDB struct {
 	StorageHashes  time.Duration
 	StorageUpdates time.Duration
 	StorageCommits time.Duration
+	TrieDBCommits  time.Duration
 
 	AccountUpdated int
 	StorageUpdated int
@@ -120,6 +125,7 @@ func New(root common.Hash, db Database) (*StateDB, error) {
 	return &StateDB{
 		db:                   db,
 		trie:                 tr,
+		originalRoot:         root,
 		stateObjects:         make(map[common.Address]*stateObject),
 		stateObjectsPending:  make(map[common.Address]struct{}),
 		stateObjectsDirty:    make(map[common.Address]struct{}),
@@ -665,6 +671,7 @@ func (s *StateDB) Copy() *StateDB {
 	state := &StateDB{
 		db:                   s.db,
 		trie:                 s.db.CopyTrie(s.trie),
+		originalRoot:         s.originalRoot,
 		stateObjects:         make(map[common.Address]*stateObject, len(s.journal.dirties)),
 		stateObjectsPending:  make(map[common.Address]struct{}, len(s.stateObjectsPending)),
 		stateObjectsDirty:    make(map[common.Address]struct{}, len(s.journal.dirties)),
@@ -852,9 +859,11 @@ func (s *StateDB) Commit(deleteEmptyObjects bool) (common.Hash, error) {
 	}
 	// Commit objects to the trie, measuring the elapsed time
 	var (
-		accountTrieNodes int
+		accountTrieNodesUpdated int
-		storageTrieNodes int
+		accountTrieNodesDeleted int
-		nodes            = trie.NewMergedNodeSet()
+		storageTrieNodesUpdated int
+		storageTrieNodesDeleted int
+		nodes                   = trie.NewMergedNodeSet()
 	)
 	codeWriter := s.db.DiskDB().NewBatch()
 	for addr := range s.stateObjectsDirty {
@@ -874,7 +883,9 @@ func (s *StateDB) Commit(deleteEmptyObjects bool) (common.Hash, error) {
 				if err := nodes.Merge(set); err != nil {
 					return common.Hash{}, err
 				}
-				storageTrieNodes += set.Len()
+				updates, deleted := set.Size()
+				storageTrieNodesUpdated += updates
+				storageTrieNodesDeleted += deleted
 			}
 		}
 		// If the contract is destructed, the storage is still left in the
@@ -904,7 +915,7 @@ func (s *StateDB) Commit(deleteEmptyObjects bool) (common.Hash, error) {
 		if err := nodes.Merge(set); err != nil {
 			return common.Hash{}, err
 		}
-		accountTrieNodes = set.Len()
+		accountTrieNodesUpdated, accountTrieNodesDeleted = set.Size()
 	}
 	// Report the commit metrics
 	s.AccountCommits += time.Since(start)
@@ -913,18 +924,32 @@ func (s *StateDB) Commit(deleteEmptyObjects bool) (common.Hash, error) {
 	storageUpdatedMeter.Mark(int64(s.StorageUpdated))
 	accountDeletedMeter.Mark(int64(s.AccountDeleted))
 	storageDeletedMeter.Mark(int64(s.StorageDeleted))
-	accountTrieCommittedMeter.Mark(int64(accountTrieNodes))
+	accountTrieUpdatedMeter.Mark(int64(accountTrieNodesUpdated))
-	storageTriesCommittedMeter.Mark(int64(storageTrieNodes))
+	accountTrieDeletedMeter.Mark(int64(accountTrieNodesDeleted))
+	storageTriesUpdatedMeter.Mark(int64(storageTrieNodesUpdated))
+	storageTriesDeletedMeter.Mark(int64(storageTrieNodesDeleted))
 	s.AccountUpdated, s.AccountDeleted = 0, 0
 	s.StorageUpdated, s.StorageDeleted = 0, 0
 
 	if len(s.stateObjectsDestruct) > 0 {
 		s.stateObjectsDestruct = make(map[common.Address]struct{})
 	}
-	if err := s.db.TrieDB().Update(nodes); err != nil {
+	if root == (common.Hash{}) {
-		return common.Hash{}, err
+		root = types.EmptyRootHash
 	}
-	return root, err
+	origin := s.originalRoot
+	if origin == (common.Hash{}) {
+		origin = types.EmptyRootHash
+	}
+	if root != origin {
+		start := time.Now()
+		if err := s.db.TrieDB().Update(nodes); err != nil {
+			return common.Hash{}, err
+		}
+		s.originalRoot = root
+		s.TrieDBCommits += time.Since(start)
+	}
+	return root, nil
 }
 
 // Prepare handles the preparatory steps for executing a state transition with.

core/state/sync_test.go

@@ -105,7 +105,7 @@ func checkTrieConsistency(db ethdb.KeyValueStore, root common.Hash) error {
 	if v, _ := db.Get(root[:]); v == nil {
 		return nil // Consider a non existent state consistent.
 	}
-	trie, err := trie.New(common.Hash{}, root, trie.NewDatabase(db))
+	trie, err := trie.New(trie.StateTrieID(root), trie.NewDatabase(db))
 	if err != nil {
 		return err
 	}
@@ -174,7 +174,7 @@ func testIterativeStateSync(t *testing.T, count int, commit bool, bypath bool) {
 	if commit {
 		srcDb.TrieDB().Commit(srcRoot, false)
 	}
-	srcTrie, _ := trie.New(common.Hash{}, srcRoot, srcDb.TrieDB())
+	srcTrie, _ := trie.New(trie.StateTrieID(srcRoot), srcDb.TrieDB())
 
 	// Create a destination state and sync with the scheduler
 	dstDb := rawdb.NewMemoryDatabase()
@@ -222,7 +222,8 @@ func testIterativeStateSync(t *testing.T, count int, commit bool, bypath bool) {
 					if err := rlp.DecodeBytes(srcTrie.Get(node.syncPath[0]), &acc); err != nil {
 						t.Fatalf("failed to decode account on path %x: %v", node.syncPath[0], err)
 					}
-					stTrie, err := trie.New(common.BytesToHash(node.syncPath[0]), acc.Root, srcDb.TrieDB())
+					id := trie.StorageTrieID(srcRoot, common.BytesToHash(node.syncPath[0]), acc.Root)
+					stTrie, err := trie.New(id, srcDb.TrieDB())
 					if err != nil {
 						t.Fatalf("failed to retriev storage trie for path %x: %v", node.syncPath[1], err)
 					}

eth/api_debug.go

@@ -286,11 +286,11 @@ func (api *DebugAPI) getModifiedAccounts(startBlock, endBlock *types.Block) ([]c
 	}
 	triedb := api.eth.BlockChain().StateCache().TrieDB()
 
-	oldTrie, err := trie.NewStateTrie(common.Hash{}, startBlock.Root(), triedb)
+	oldTrie, err := trie.NewStateTrie(trie.StateTrieID(startBlock.Root()), triedb)
 	if err != nil {
 		return nil, err
 	}
-	newTrie, err := trie.NewStateTrie(common.Hash{}, endBlock.Root(), triedb)
+	newTrie, err := trie.NewStateTrie(trie.StateTrieID(endBlock.Root()), triedb)
 	if err != nil {
 		return nil, err
 	}

eth/downloader/downloader_test.go

@@ -192,7 +192,7 @@ func (dl *downloadTester) CurrentFastBlock() *types.Block {
 func (dl *downloadTester) FastSyncCommitHead(hash common.Hash) error {
 	// For now only check that the state trie is correct
 	if block := dl.GetBlockByHash(hash); block != nil {
-		_, err := trie.NewStateTrie(common.Hash{}, block.Root(), trie.NewDatabase(dl.stateDb))
+		_, err := trie.NewStateTrie(trie.StateTrieID(block.Root()), trie.NewDatabase(dl.stateDb))
 		return err
 	}
 	return fmt.Errorf("non existent block: %x", hash[:4])

trie/committer.go

@@ -33,13 +33,15 @@ type leaf struct {
 // insertion order.
 type committer struct {
 	nodes       *NodeSet
+	tracer      *tracer
 	collectLeaf bool
 }
 
 // newCommitter creates a new committer or picks one from the pool.
-func newCommitter(owner common.Hash, collectLeaf bool) *committer {
+func newCommitter(owner common.Hash, tracer *tracer, collectLeaf bool) *committer {
 	return &committer{
 		nodes:       NewNodeSet(owner),
+		tracer:      tracer,
 		collectLeaf: collectLeaf,
 	}
 }
@@ -51,6 +53,20 @@ func (c *committer) Commit(n node) (hashNode, *NodeSet, error) {
 	if err != nil {
 		return nil, nil, err
 	}
+	// Some nodes can be deleted from trie which can't be captured by committer
+	// itself. Iterate all deleted nodes tracked by tracer and marked them as
+	// deleted only if they are present in database previously.
+	for _, path := range c.tracer.deleteList() {
+		// There are a few possibilities for this scenario(the node is deleted
+		// but not present in database previously), for example the node was
+		// embedded in the parent and now deleted from the trie. In this case
+		// it's noop from database's perspective.
+		val := c.tracer.getPrev(path)
+		if len(val) == 0 {
+			continue
+		}
+		c.nodes.markDeleted(path, val)
+	}
 	return h.(hashNode), c.nodes, nil
 }
 
@@ -83,6 +99,12 @@ func (c *committer) commit(path []byte, n node) (node, error) {
 		if hn, ok := hashedNode.(hashNode); ok {
 			return hn, nil
 		}
+		// The short node now is embedded in its parent. Mark the node as
+		// deleted if it's present in database previously. It's equivalent
+		// as deletion from database's perspective.
+		if prev := c.tracer.getPrev(path); len(prev) != 0 {
+			c.nodes.markDeleted(path, prev)
+		}
 		return collapsed, nil
 	case *fullNode:
 		hashedKids, err := c.commitChildren(path, cn)
@@ -96,6 +118,12 @@ func (c *committer) commit(path []byte, n node) (node, error) {
 		if hn, ok := hashedNode.(hashNode); ok {
 			return hn, nil
 		}
+		// The full node now is embedded in its parent. Mark the node as
+		// deleted if it's present in database previously. It's equivalent
+		// as deletion from database's perspective.
+		if prev := c.tracer.getPrev(path); len(prev) != 0 {
+			c.nodes.markDeleted(path, prev)
+		}
 		return collapsed, nil
 	case hashNode:
 		return cn, nil
@@ -161,7 +189,7 @@ func (c *committer) store(path []byte, n node) node {
 		}
 	)
 	// Collect the dirty node to nodeset for return.
-	c.nodes.add(string(path), mnode)
+	c.nodes.markUpdated(path, mnode, c.tracer.getPrev(path))
 
 	// Collect the corresponding leaf node if it's required. We don't check
 	// full node since it's impossible to store value in fullNode. The key

trie/database.go

@@ -807,8 +807,8 @@ func (db *Database) Update(nodes *MergedNodeSet) error {
 	}
 	for _, owner := range order {
 		subset := nodes.sets[owner]
-		for _, path := range subset.paths {
+		for _, path := range subset.updates.order {
-			n, ok := subset.nodes[path]
+			n, ok := subset.updates.nodes[path]
 			if !ok {
 				return fmt.Errorf("missing node %x %v", owner, path)
 			}
@@ -849,6 +849,34 @@ func (db *Database) Size() (common.StorageSize, common.StorageSize) {
 	return db.dirtiesSize + db.childrenSize + metadataSize - metarootRefs, preimageSize
 }
 
+// GetReader retrieves a node reader belonging to the given state root.
+func (db *Database) GetReader(root common.Hash) Reader {
+	return newHashReader(db)
+}
+
+// hashReader is reader of hashDatabase which implements the Reader interface.
+type hashReader struct {
+	db *Database
+}
+
+// newHashReader initializes the hash reader.
+func newHashReader(db *Database) *hashReader {
+	return &hashReader{db: db}
+}
+
+// Node retrieves the trie node with the given node hash.
+// No error will be returned if the node is not found.
+func (reader *hashReader) Node(_ common.Hash, _ []byte, hash common.Hash) (node, error) {
+	return reader.db.node(hash), nil
+}
+
+// NodeBlob retrieves the RLP-encoded trie node blob with the given node hash.
+// No error will be returned if the node is not found.
+func (reader *hashReader) NodeBlob(_ common.Hash, _ []byte, hash common.Hash) ([]byte, error) {
+	blob, _ := reader.db.Node(hash)
+	return blob, nil
+}
+
 // CommitPreimages flushes the dangling preimages to disk. It is meant to be
 // called when closing the blockchain object, so that preimages are persisted
 // to the database.

trie/iterator.go

@@ -376,7 +376,12 @@ func (it *nodeIterator) resolveHash(hash hashNode, path []byte) (node, error) {
 			}
 		}
 	}
-	return it.trie.resolveHash(hash, path)
+	// Retrieve the specified node from the underlying node reader.
+	// it.trie.resolveAndTrack is not used since in that function the
+	// loaded blob will be tracked, while it's not required here since
+	// all loaded nodes won't be linked to trie at all and track nodes
+	// may lead to out-of-memory issue.
+	return it.trie.reader.node(path, common.BytesToHash(hash))
 }
 
 func (it *nodeIterator) resolveBlob(hash hashNode, path []byte) ([]byte, error) {
@@ -385,7 +390,12 @@ func (it *nodeIterator) resolveBlob(hash hashNode, path []byte) ([]byte, error)
 			return blob, nil
 		}
 	}
-	return it.trie.resolveBlob(hash, path)
+	// Retrieve the specified node from the underlying node reader.
+	// it.trie.resolveAndTrack is not used since in that function the
+	// loaded blob will be tracked, while it's not required here since
+	// all loaded nodes won't be linked to trie at all and track nodes
+	// may lead to out-of-memory issue.
+	return it.trie.reader.nodeBlob(path, common.BytesToHash(hash))
 }
 
 func (st *nodeIteratorState) resolve(it *nodeIterator, path []byte) error {

trie/iterator_test.go

@@ -66,7 +66,7 @@ func TestIterator(t *testing.T) {
 	}
 	db.Update(NewWithNodeSet(nodes))
 
-	trie, _ = New(common.Hash{}, root, db)
+	trie, _ = New(TrieID(root), db)
 	found := make(map[string]string)
 	it := NewIterator(trie.NodeIterator(nil))
 	for it.Next() {
@@ -227,7 +227,7 @@ func TestDifferenceIterator(t *testing.T) {
 	}
 	rootA, nodesA, _ := triea.Commit(false)
 	dba.Update(NewWithNodeSet(nodesA))
-	triea, _ = New(common.Hash{}, rootA, dba)
+	triea, _ = New(TrieID(rootA), dba)
 
 	dbb := NewDatabase(rawdb.NewMemoryDatabase())
 	trieb := NewEmpty(dbb)
@@ -236,7 +236,7 @@ func TestDifferenceIterator(t *testing.T) {
 	}
 	rootB, nodesB, _ := trieb.Commit(false)
 	dbb.Update(NewWithNodeSet(nodesB))
-	trieb, _ = New(common.Hash{}, rootB, dbb)
+	trieb, _ = New(TrieID(rootB), dbb)
 
 	found := make(map[string]string)
 	di, _ := NewDifferenceIterator(triea.NodeIterator(nil), trieb.NodeIterator(nil))
@@ -269,7 +269,7 @@ func TestUnionIterator(t *testing.T) {
 	}
 	rootA, nodesA, _ := triea.Commit(false)
 	dba.Update(NewWithNodeSet(nodesA))
-	triea, _ = New(common.Hash{}, rootA, dba)
+	triea, _ = New(TrieID(rootA), dba)
 
 	dbb := NewDatabase(rawdb.NewMemoryDatabase())
 	trieb := NewEmpty(dbb)
@@ -278,7 +278,7 @@ func TestUnionIterator(t *testing.T) {
 	}
 	rootB, nodesB, _ := trieb.Commit(false)
 	dbb.Update(NewWithNodeSet(nodesB))
-	trieb, _ = New(common.Hash{}, rootB, dbb)
+	trieb, _ = New(TrieID(rootB), dbb)
 
 	di, _ := NewUnionIterator([]NodeIterator{triea.NodeIterator(nil), trieb.NodeIterator(nil)})
 	it := NewIterator(di)
@@ -356,7 +356,7 @@ func testIteratorContinueAfterError(t *testing.T, memonly bool) {
 	}
 	for i := 0; i < 20; i++ {
 		// Create trie that will load all nodes from DB.
-		tr, _ := New(common.Hash{}, tr.Hash(), triedb)
+		tr, _ := New(TrieID(tr.Hash()), triedb)
 
 		// Remove a random Node from the database. It can't be the root Node
 		// because that one is already loaded.
@@ -445,7 +445,7 @@ func testIteratorContinueAfterSeekError(t *testing.T, memonly bool) {
 	}
 	// Create a new iterator that seeks to "bars". Seeking can't proceed because
 	// the node is missing.
-	tr, _ := New(common.Hash{}, root, triedb)
+	tr, _ := New(TrieID(root), triedb)
 	it := tr.NodeIterator([]byte("bars"))
 	missing, ok := it.Error().(*MissingNodeError)
 	if !ok {
@@ -529,7 +529,7 @@ func makeLargeTestTrie() (*Database, *StateTrie, *loggingDb) {
 	// Create an empty trie
 	logDb := &loggingDb{0, memorydb.New()}
 	triedb := NewDatabase(logDb)
-	trie, _ := NewStateTrie(common.Hash{}, common.Hash{}, triedb)
+	trie, _ := NewStateTrie(TrieID(common.Hash{}), triedb)
 
 	// Fill it with some arbitrary data
 	for i := 0; i < 10000; i++ {

trie/nodeset.go

@@ -18,6 +18,8 @@ package trie
 
 import (
 	"fmt"
+	"reflect"
+	"strings"
 
 	"github.com/XinFinOrg/XDPoSChain/common"
 )
@@ -25,18 +27,77 @@ import (
 // memoryNode is all the information we know about a single cached trie node
 // in the memory.
 type memoryNode struct {
-	hash common.Hash // Node hash, computed by hashing rlp value
+	hash common.Hash // Node hash, computed by hashing rlp value, empty for deleted nodes
-	size uint16      // Byte size of the useful cached data
+	size uint16      // Byte size of the useful cached data, 0 for deleted nodes
-	node node        // Cached collapsed trie node, or raw rlp data
+	node node        // Cached collapsed trie node, or raw rlp data, nil for deleted nodes
+}
+
+// memoryNodeSize is the raw size of a memoryNode data structure without any
+// node data included. It's an approximate size, but should be a lot better
+// than not counting them.
+// nolint:unused
+var memoryNodeSize = int(reflect.TypeOf(memoryNode{}).Size())
+
+// memorySize returns the total memory size used by this node.
+// nolint:unused
+func (n *memoryNode) memorySize(key int) int {
+	return int(n.size) + memoryNodeSize + key
+}
+
+// rlp returns the raw rlp encoded blob of the cached trie node, either directly
+// from the cache, or by regenerating it from the collapsed node.
+// nolint:unused
+func (n *memoryNode) rlp() []byte {
+	if node, ok := n.node.(rawNode); ok {
+		return node
+	}
+	return nodeToBytes(n.node)
+}
+
+// obj returns the decoded and expanded trie node, either directly from the cache,
+// or by regenerating it from the rlp encoded blob.
+// nolint:unused
+func (n *memoryNode) obj() node {
+	if node, ok := n.node.(rawNode); ok {
+		return mustDecodeNode(n.hash[:], node)
+	}
+	return expandNode(n.hash[:], n.node)
+}
+
+// nodeWithPrev wraps the memoryNode with the previous node value.
+type nodeWithPrev struct {
+	*memoryNode
+	prev []byte // RLP-encoded previous value, nil means it's non-existent
+}
+
+// unwrap returns the internal memoryNode object.
+// nolint:unused
+func (n *nodeWithPrev) unwrap() *memoryNode {
+	return n.memoryNode
+}
+
+// memorySize returns the total memory size used by this node. It overloads
+// the function in memoryNode by counting the size of previous value as well.
+// nolint: unused
+func (n *nodeWithPrev) memorySize(key int) int {
+	return n.memoryNode.memorySize(key) + len(n.prev)
+}
+
+// nodesWithOrder represents a collection of dirty nodes which includes
+// newly-inserted and updated nodes. The modification order of all nodes
+// is represented by order list.
+type nodesWithOrder struct {
+	order []string                 // the path list of dirty nodes, sort by insertion order
+	nodes map[string]*nodeWithPrev // the map of dirty nodes, keyed by node path
 }
 
 // NodeSet contains all dirty nodes collected during the commit operation.
 // Each node is keyed by path. It's not thread-safe to use.
 type NodeSet struct {
-	owner  common.Hash            // the identifier of the trie
+	owner   common.Hash       // the identifier of the trie
-	paths  []string               // the path of dirty nodes, sort by insertion order
+	updates *nodesWithOrder   // the set of updated nodes(newly inserted, updated)
-	nodes  map[string]*memoryNode // the map of dirty nodes, keyed by node path
+	deletes map[string][]byte // the map of deleted nodes, keyed by node
-	leaves []*leaf                // the list of dirty leaves
+	leaves  []*leaf           // the list of dirty leaves
 }
 
 // NewNodeSet initializes an empty node set to be used for tracking dirty nodes
@@ -45,24 +106,78 @@ type NodeSet struct {
 func NewNodeSet(owner common.Hash) *NodeSet {
 	return &NodeSet{
 		owner: owner,
-		nodes: make(map[string]*memoryNode),
+		updates: &nodesWithOrder{
+			nodes: make(map[string]*nodeWithPrev),
+		},
+		deletes: make(map[string][]byte),
 	}
 }
 
-// add caches node with provided path and node object.
+// NewNodeSetWithDeletion initializes the nodeset with provided deletion set.
-func (set *NodeSet) add(path string, node *memoryNode) {
+func NewNodeSetWithDeletion(owner common.Hash, paths [][]byte, prev [][]byte) *NodeSet {
-	set.paths = append(set.paths, path)
+	set := NewNodeSet(owner)
-	set.nodes[path] = node
+	for i, path := range paths {
+		set.markDeleted(path, prev[i])
+	}
+	return set
 }
 
-// addLeaf caches the provided leaf node.
+// markUpdated marks the node as dirty(newly-inserted or updated) with provided
+// node path, node object along with its previous value.
+func (set *NodeSet) markUpdated(path []byte, node *memoryNode, prev []byte) {
+	set.updates.order = append(set.updates.order, string(path))
+	set.updates.nodes[string(path)] = &nodeWithPrev{
+		memoryNode: node,
+		prev:       prev,
+	}
+}
+
+// markDeleted marks the node as deleted with provided path and previous value.
+func (set *NodeSet) markDeleted(path []byte, prev []byte) {
+	set.deletes[string(path)] = prev
+}
+
+// addLeaf collects the provided leaf node into set.
 func (set *NodeSet) addLeaf(node *leaf) {
 	set.leaves = append(set.leaves, node)
 }
 
-// Len returns the number of dirty nodes contained in the set.
+// Size returns the number of updated and deleted nodes contained in the set.
-func (set *NodeSet) Len() int {
+func (set *NodeSet) Size() (int, int) {
-	return len(set.nodes)
+	return len(set.updates.order), len(set.deletes)
+}
+
+// Hashes returns the hashes of all updated nodes. TODO(rjl493456442) how can
+// we get rid of it?
+func (set *NodeSet) Hashes() []common.Hash {
+	var ret []common.Hash
+	for _, node := range set.updates.nodes {
+		ret = append(ret, node.hash)
+	}
+	return ret
+}
+
+// Summary returns a string-representation of the NodeSet.
+func (set *NodeSet) Summary() string {
+	var out = new(strings.Builder)
+	fmt.Fprintf(out, "nodeset owner: %v\n", set.owner)
+	if set.updates != nil {
+		for _, key := range set.updates.order {
+			updated := set.updates.nodes[key]
+			if updated.prev != nil {
+				fmt.Fprintf(out, "  [*]: %x -> %v prev: %x\n", key, updated.hash, updated.prev)
+			} else {
+				fmt.Fprintf(out, "  [+]: %x -> %v\n", key, updated.hash)
+			}
+		}
+	}
+	for k, n := range set.deletes {
+		fmt.Fprintf(out, "  [-]: %x -> %x\n", k, n)
+	}
+	for _, n := range set.leaves {
+		fmt.Fprintf(out, "[leaf]: %v\n", n)
+	}
+	return out.String()
 }
 
 // MergedNodeSet represents a merged dirty node set for a group of tries.

trie/proof.go

@@ -22,7 +22,6 @@ import (
 	"fmt"
 
 	"github.com/XinFinOrg/XDPoSChain/common"
-	"github.com/XinFinOrg/XDPoSChain/core/rawdb"
 	"github.com/XinFinOrg/XDPoSChain/ethdb"
 	"github.com/XinFinOrg/XDPoSChain/log"
 )
@@ -60,8 +59,13 @@ func (t *Trie) Prove(key []byte, fromLevel uint, proofDb ethdb.KeyValueWriter) e
 			key = key[1:]
 			nodes = append(nodes, n)
 		case hashNode:
+			// Retrieve the specified node from the underlying node reader.
+			// trie.resolveAndTrack is not used since in that function the
+			// loaded blob will be tracked, while it's not required here since
+			// all loaded nodes won't be linked to trie at all and track nodes
+			// may lead to out-of-memory issue.
 			var err error
-			tn, err = t.resolveHash(n, prefix)
+			tn, err = t.reader.node(prefix, common.BytesToHash(n))
 			if err != nil {
 				log.Error("Unhandled trie error in Trie.Prove", "err", err)
 				return err
@@ -559,7 +563,7 @@ func VerifyRangeProof(rootHash common.Hash, firstKey []byte, lastKey []byte, key
 	}
 	// Rebuild the trie with the leaf stream, the shape of trie
 	// should be same with the original one.
-	tr := &Trie{root: root, db: NewDatabase(rawdb.NewMemoryDatabase())}
+	tr := &Trie{root: root, reader: newEmptyReader()}
 	if empty {
 		tr.root = nil
 	}

trie/secure_trie.go

@@ -29,8 +29,13 @@ type SecureTrie = StateTrie
 
 // NewSecure creates a new StateTrie.
 // Deprecated: use NewStateTrie.
-func NewSecure(owner common.Hash, root common.Hash, db *Database) (*SecureTrie, error) {
+func NewSecure(stateRoot common.Hash, owner common.Hash, root common.Hash, db *Database) (*SecureTrie, error) {
-	return NewStateTrie(owner, root, db)
+	id := &ID{
+		StateRoot: stateRoot,
+		Owner:     owner,
+		Root:      root,
+	}
+	return NewStateTrie(id, db)
 }
 
 // StateTrie wraps a trie with key hashing. In a stateTrie trie, all
@@ -56,11 +61,11 @@ type StateTrie struct {
 // If root is the zero hash or the sha3 hash of an empty string, the
 // trie is initially empty. Otherwise, New will panic if db is nil
 // and returns MissingNodeError if the root node cannot be found.
-func NewStateTrie(owner common.Hash, root common.Hash, db *Database) (*StateTrie, error) {
+func NewStateTrie(id *ID, db *Database) (*StateTrie, error) {
 	if db == nil {
 		panic("trie.NewStateTrie called without a database")
 	}
-	trie, err := New(owner, root, db)
+	trie, err := New(id, db)
 	if err != nil {
 		return nil, err
 	}

trie/secure_trie_test.go

@@ -29,7 +29,7 @@ import (
 )
 
 func newEmptySecure() *StateTrie {
-	trie, _ := NewStateTrie(common.Hash{}, common.Hash{}, NewDatabase(memorydb.New()))
+	trie, _ := NewStateTrie(TrieID(common.Hash{}), NewDatabase(memorydb.New()))
 	return trie
 }
 
@@ -37,7 +37,7 @@ func newEmptySecure() *StateTrie {
 func makeTestStateTrie() (*Database, *StateTrie, map[string][]byte) {
 	// Create an empty trie
 	triedb := NewDatabase(memorydb.New())
-	trie, _ := NewStateTrie(common.Hash{}, common.Hash{}, triedb)
+	trie, _ := NewStateTrie(TrieID(common.Hash{}), triedb)
 
 	// Fill it with some arbitrary data
 	content := make(map[string][]byte)
@@ -66,7 +66,7 @@ func makeTestStateTrie() (*Database, *StateTrie, map[string][]byte) {
 		panic(fmt.Errorf("failed to commit db %v", err))
 	}
 	// Re-create the trie based on the new state
-	trie, _ = NewSecure(common.Hash{}, root, triedb)
+	trie, _ = NewStateTrie(TrieID(root), triedb)
 	return triedb, trie, content
 }
 

trie/sync_test.go

@@ -31,7 +31,7 @@ import (
 func makeTestTrie() (*Database, *StateTrie, map[string][]byte) {
 	// Create an empty trie
 	triedb := NewDatabase(memorydb.New())
-	trie, _ := NewStateTrie(common.Hash{}, common.Hash{}, triedb)
+	trie, _ := NewStateTrie(TrieID(common.Hash{}), triedb)
 
 	// Fill it with some arbitrary data
 	content := make(map[string][]byte)
@@ -60,7 +60,7 @@ func makeTestTrie() (*Database, *StateTrie, map[string][]byte) {
 		panic(fmt.Errorf("failed to commit db %v", err))
 	}
 	// Re-create the trie based on the new state
-	trie, _ = NewSecure(common.Hash{}, root, triedb)
+	trie, _ = NewStateTrie(TrieID(root), triedb)
 	return triedb, trie, content
 }
 
@@ -68,7 +68,7 @@ func makeTestTrie() (*Database, *StateTrie, map[string][]byte) {
 // content map.
 func checkTrieContents(t *testing.T, db *Database, root []byte, content map[string][]byte) {
 	// Check root availability and trie contents
-	trie, err := NewStateTrie(common.Hash{}, common.BytesToHash(root), db)
+	trie, err := NewStateTrie(TrieID(common.BytesToHash(root)), db)
 	if err != nil {
 		t.Fatalf("failed to create trie at %x: %v", root, err)
 	}
@@ -85,7 +85,7 @@ func checkTrieContents(t *testing.T, db *Database, root []byte, content map[stri
 // checkTrieConsistency checks that all nodes in a trie are indeed present.
 func checkTrieConsistency(db *Database, root common.Hash) error {
 	// Create and iterate a trie rooted in a subnode
-	trie, err := NewStateTrie(common.Hash{}, root, db)
+	trie, err := NewStateTrie(TrieID(root), db)
 	if err != nil {
 		return nil // Consider a non existent state consistent
 	}
@@ -106,8 +106,8 @@ type trieElement struct {
 func TestEmptySync(t *testing.T) {
 	dbA := NewDatabase(memorydb.New())
 	dbB := NewDatabase(memorydb.New())
-	emptyA := NewEmpty(dbA)
+	emptyA, _ := New(TrieID(common.Hash{}), dbA)
-	emptyB, _ := New(common.Hash{}, types.EmptyRootHash, dbB)
+	emptyB, _ := New(TrieID(types.EmptyRootHash), dbB)
 
 	for i, trie := range []*Trie{emptyA, emptyB} {
 		sync := NewSync(trie.Hash(), memorydb.New(), nil)

trie/trie.go

@@ -63,6 +63,9 @@ type Trie struct {
 	// only for reading purpose and not available for writing.
 	db *Database
 
+	// reader is the handler trie can retrieve nodes from.
+	reader *trieReader
+
 	// tracer is the tool to track the trie changes.
 	// It will be reset after each commit operation.
 	tracer *tracer
@@ -84,25 +87,30 @@ func (t *Trie) Copy() *Trie {
 		owner:    t.owner,
 		unhashed: t.unhashed,
 		db:       t.db,
+		reader:   t.reader,
 		tracer:   t.tracer.copy(),
 	}
 }
 
-// New creates a trie with an existing root node from db and an assigned
+// New creates the trie instance with provided trie id and the read-only
-// owner for storage proximity.
+// database. The state specified by trie id must be available, otherwise
-//
+// an error will be returned. The trie root specified by trie id can be
-// If root is the zero hash or the sha3 hash of an empty string, the
+// zero hash or the sha3 hash of an empty string, then trie is initially
-// trie is initially empty and does not require a database. Otherwise,
+// empty, otherwise, the root node must be present in database or returns
-// New will panic if db is nil and returns a MissingNodeError if root does
+// a MissingNodeError if not.
-// not exist in the database. Accessing the trie loads nodes from db on demand.
+func New(id *ID, db *Database) (*Trie, error) {
-func New(owner common.Hash, root common.Hash, db *Database) (*Trie, error) {
+	reader, err := newTrieReader(id.StateRoot, id.Owner, db)
+	if err != nil {
+		return nil, err
+	}
 	trie := &Trie{
-		owner: owner,
+		owner:  id.Owner,
-		db:    db,
+		db:     db,
+		reader: reader,
 		//tracer: newTracer(),
 	}
-	if root != (common.Hash{}) && root != types.EmptyRootHash {
+	if id.Root != (common.Hash{}) && id.Root != types.EmptyRootHash {
-		rootnode, err := trie.resolveHash(root[:], nil)
+		rootnode, err := trie.resolveAndTrack(id.Root[:], nil)
 		if err != nil {
 			return nil, err
 		}
@@ -113,7 +121,7 @@ func New(owner common.Hash, root common.Hash, db *Database) (*Trie, error) {
 
 // NewEmpty is a shortcut to create empty tree. It's mostly used in tests.
 func NewEmpty(db *Database) *Trie {
-	tr, _ := New(common.Hash{}, common.Hash{}, db)
+	tr, _ := New(TrieID(common.Hash{}), db)
 	return tr
 }
 
@@ -169,7 +177,7 @@ func (t *Trie) tryGet(origNode node, key []byte, pos int) (value []byte, newnode
 		}
 		return value, n, didResolve, err
 	case hashNode:
-		child, err := t.resolveHash(n, key[:pos])
+		child, err := t.resolveAndTrack(n, key[:pos])
 		if err != nil {
 			return nil, n, true, err
 		}
@@ -215,7 +223,7 @@ func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, new
 		if hash == nil {
 			return nil, origNode, 0, errors.New("non-consensus node")
 		}
-		blob, err := t.db.Node(common.BytesToHash(hash))
+		blob, err := t.reader.nodeBlob(path, common.BytesToHash(hash))
 		return blob, origNode, 1, err
 	}
 	// Path still needs to be traversed, descend into children
@@ -245,7 +253,7 @@ func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, new
 		return item, n, resolved, err
 
 	case hashNode:
-		child, err := t.resolveHash(n, path[:pos])
+		child, err := t.resolveAndTrack(n, path[:pos])
 		if err != nil {
 			return nil, n, 1, err
 		}
@@ -294,7 +302,7 @@ func (t *Trie) tryGetBestLeftKeyAndValue(origNode node, prefix []byte) (key []by
 			return key, value, n, didResolve, err
 		}
 	case hashNode:
-		child, err := t.resolveHash(n, nil)
+		child, err := t.resolveAndTrack(n, nil)
 		if err != nil {
 			return nil, nil, n, true, err
 		}
@@ -362,7 +370,7 @@ func (t *Trie) tryGetAllLeftKeyAndValue(origNode node, prefix []byte, limit []by
 		}
 		return keys, values, n, didResolve, err
 	case hashNode:
-		child, err := t.resolveHash(n, nil)
+		child, err := t.resolveAndTrack(n, nil)
 		if err != nil {
 			return nil, nil, n, true, err
 		}
@@ -410,7 +418,7 @@ func (t *Trie) tryGetBestRightKeyAndValue(origNode node, prefix []byte) (key []b
 			return key, value, n, didResolve, err
 		}
 	case hashNode:
-		child, err := t.resolveHash(n, nil)
+		child, err := t.resolveAndTrack(n, nil)
 		if err != nil {
 			return nil, nil, n, true, err
 		}
@@ -531,7 +539,7 @@ func (t *Trie) insert(n node, prefix, key []byte, value node) (bool, node, error
 		// We've hit a part of the trie that isn't loaded yet. Load
 		// the Node and insert into it. This leaves all child nodes on
 		// the path to the value in the trie.
-		rn, err := t.resolveHash(n, prefix)
+		rn, err := t.resolveAndTrack(n, prefix)
 		if err != nil {
 			return false, nil, err
 		}
@@ -685,7 +693,7 @@ func (t *Trie) delete(n node, prefix, key []byte) (bool, node, error) {
 		// We've hit a part of the trie that isn't loaded yet. Load
 		// the Node and delete from it. This leaves all child nodes on
 		// the path to the value in the trie.
-		rn, err := t.resolveHash(n, prefix)
+		rn, err := t.resolveAndTrack(n, prefix)
 		if err != nil {
 			return false, nil, err
 		}
@@ -709,30 +717,22 @@ func concat(s1 []byte, s2 ...byte) []byte {
 
 func (t *Trie) resolve(n node, prefix []byte) (node, error) {
 	if n, ok := n.(hashNode); ok {
-		return t.resolveHash(n, prefix)
+		return t.resolveAndTrack(n, prefix)
 	}
 	return n, nil
 }
 
-// resolveHash loads node from the underlying database with the provided
+// resolveAndTrack loads node from the underlying store with the given node hash
-// node hash and path prefix.
+// and path prefix and also tracks the loaded node blob in tracer treated as the
-func (t *Trie) resolveHash(n hashNode, prefix []byte) (node, error) {
+// node's original value. The rlp-encoded blob is preferred to be loaded from
-	hash := common.BytesToHash(n)
+// database because it's easy to decode node while complex to encode node to blob.
-	if node := t.db.node(hash); node != nil {
+func (t *Trie) resolveAndTrack(n hashNode, prefix []byte) (node, error) {
-		return node, nil
+	blob, err := t.reader.nodeBlob(prefix, common.BytesToHash(n))
+	if err != nil {
+		return nil, err
 	}
-	return nil, &MissingNodeError{Owner: t.owner, NodeHash: hash, Path: prefix}
+	t.tracer.onRead(prefix, blob)
-}
+	return mustDecodeNode(n, blob), nil
-
-// resolveHash loads rlp-encoded node blob from the underlying database
-// with the provided node hash and path prefix.
-func (t *Trie) resolveBlob(n hashNode, prefix []byte) ([]byte, error) {
-	hash := common.BytesToHash(n)
-	blob, _ := t.db.Node(hash)
-	if len(blob) != 0 {
-		return blob, nil
-	}
-	return nil, &MissingNodeError{Owner: t.owner, NodeHash: hash, Path: prefix}
 }
 
 // Hash returns the root hash of the trie. It does not write to the
@@ -750,9 +750,6 @@ func (t *Trie) Hash() common.Hash {
 // Once the trie is committed, it's not usable anymore. A new trie must
 // be created with new root and updated trie database for following usage
 func (t *Trie) Commit(collectLeaf bool) (common.Hash, *NodeSet, error) {
-	if t.db == nil {
-		panic("commit called on trie with nil database")
-	}
 	defer t.tracer.reset()
 
 	if t.root == nil {
@@ -770,7 +767,7 @@ func (t *Trie) Commit(collectLeaf bool) (common.Hash, *NodeSet, error) {
 		t.root = hashedNode
 		return rootHash, nil, nil
 	}
-	h := newCommitter(t.owner, collectLeaf)
+	h := newCommitter(t.owner, t.tracer, collectLeaf)
 	newRoot, nodes, err := h.Commit(t.root)
 	if err != nil {
 		return common.Hash{}, nil, err
@@ -797,6 +794,5 @@ func (t *Trie) Reset() {
 	t.root = nil
 	t.owner = common.Hash{}
 	t.unhashed = 0
-	//t.db = nil
 	t.tracer.reset()
 }

trie/trie_id.go

@@ -0,0 +1,55 @@
+// Copyright 2022 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>
+
+package trie
+
+import "github.com/XinFinOrg/XDPoSChain/common"
+
+// ID is the identifier for uniquely identifying a trie.
+type ID struct {
+	StateRoot common.Hash // The root of the corresponding state(block.root)
+	Owner     common.Hash // The contract address hash which the trie belongs to
+	Root      common.Hash // The root hash of trie
+}
+
+// StateTrieID constructs an identifier for state trie with the provided state root.
+func StateTrieID(root common.Hash) *ID {
+	return &ID{
+		StateRoot: root,
+		Owner:     common.Hash{},
+		Root:      root,
+	}
+}
+
+// StorageTrieID constructs an identifier for storage trie which belongs to a certain
+// state and contract specified by the stateRoot and owner.
+func StorageTrieID(stateRoot common.Hash, owner common.Hash, root common.Hash) *ID {
+	return &ID{
+		StateRoot: stateRoot,
+		Owner:     owner,
+		Root:      root,
+	}
+}
+
+// TrieID constructs an identifier for a standard trie(not a second-layer trie)
+// with provided root. It's mostly used in tests and some other tries like CHT trie.
+func TrieID(root common.Hash) *ID {
+	return &ID{
+		StateRoot: root,
+		Owner:     common.Hash{},
+		Root:      root,
+	}
+}

trie/trie_reader.go

@@ -0,0 +1,106 @@
+// Copyright 2022 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package trie
+
+import (
+	"fmt"
+
+	"github.com/XinFinOrg/XDPoSChain/common"
+)
+
+// Reader wraps the Node and NodeBlob method of a backing trie store.
+type Reader interface {
+	// Node retrieves the trie node with the provided trie identifier, hexary
+	// node path and the corresponding node hash.
+	// No error will be returned if the node is not found.
+	Node(owner common.Hash, path []byte, hash common.Hash) (node, error)
+
+	// NodeBlob retrieves the RLP-encoded trie node blob with the provided trie
+	// identifier, hexary node path and the corresponding node hash.
+	// No error will be returned if the node is not found.
+	NodeBlob(owner common.Hash, path []byte, hash common.Hash) ([]byte, error)
+}
+
+// NodeReader wraps all the necessary functions for accessing trie node.
+type NodeReader interface {
+	// GetReader returns a reader for accessing all trie nodes with provided
+	// state root. Nil is returned in case the state is not available.
+	GetReader(root common.Hash) Reader
+}
+
+// trieReader is a wrapper of the underlying node reader. It's not safe
+// for concurrent usage.
+type trieReader struct {
+	owner  common.Hash
+	reader Reader
+	banned map[string]struct{} // Marker to prevent node from being accessed, for tests
+}
+
+// newTrieReader initializes the trie reader with the given node reader.
+func newTrieReader(stateRoot, owner common.Hash, db NodeReader) (*trieReader, error) {
+	reader := db.GetReader(stateRoot)
+	if reader == nil {
+		return nil, fmt.Errorf("state not found #%x", stateRoot)
+	}
+	return &trieReader{owner: owner, reader: reader}, nil
+}
+
+// newEmptyReader initializes the pure in-memory reader. All read operations
+// should be forbidden and returns the MissingNodeError.
+func newEmptyReader() *trieReader {
+	return &trieReader{}
+}
+
+// node retrieves the trie node with the provided trie node information.
+// An MissingNodeError will be returned in case the node is not found or
+// any error is encountered.
+func (r *trieReader) node(path []byte, hash common.Hash) (node, error) {
+	// Perform the logics in tests for preventing trie node access.
+	if r.banned != nil {
+		if _, ok := r.banned[string(path)]; ok {
+			return nil, &MissingNodeError{Owner: r.owner, NodeHash: hash, Path: path}
+		}
+	}
+	if r.reader == nil {
+		return nil, &MissingNodeError{Owner: r.owner, NodeHash: hash, Path: path}
+	}
+	node, err := r.reader.Node(r.owner, path, hash)
+	if err != nil || node == nil {
+		return nil, &MissingNodeError{Owner: r.owner, NodeHash: hash, Path: path, err: err}
+	}
+	return node, nil
+}
+
+// node retrieves the rlp-encoded trie node with the provided trie node
+// information. An MissingNodeError will be returned in case the node is
+// not found or any error is encountered.
+func (r *trieReader) nodeBlob(path []byte, hash common.Hash) ([]byte, error) {
+	// Perform the logics in tests for preventing trie node access.
+	if r.banned != nil {
+		if _, ok := r.banned[string(path)]; ok {
+			return nil, &MissingNodeError{Owner: r.owner, NodeHash: hash, Path: path}
+		}
+	}
+	if r.reader == nil {
+		return nil, &MissingNodeError{Owner: r.owner, NodeHash: hash, Path: path}
+	}
+	blob, err := r.reader.NodeBlob(r.owner, path, hash)
+	if err != nil || len(blob) == 0 {
+		return nil, &MissingNodeError{Owner: r.owner, NodeHash: hash, Path: path, err: err}
+	}
+	return blob, nil
+}

trie/trie_test.go

@@ -66,7 +66,8 @@ func TestNull(t *testing.T) {
 }
 
 func TestMissingRoot(t *testing.T) {
-	trie, err := New(common.Hash{}, common.HexToHash("0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"), NewDatabase(memorydb.New()))
+	root := common.HexToHash("0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33")
+	trie, err := New(TrieID(root), NewDatabase(memorydb.New()))
 	if trie != nil {
 		t.Error("New returned non-nil trie for invalid root")
 	}
@@ -91,27 +92,27 @@ func testMissingNode(t *testing.T, memonly bool) {
 		triedb.Commit(root, true)
 	}
 
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	_, err := trie.TryGet([]byte("120000"))
 	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	_, err = trie.TryGet([]byte("120099"))
 	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	_, err = trie.TryGet([]byte("123456"))
 	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	err = trie.TryUpdate([]byte("120099"), []byte("zxcvzxcvzxcvzxcvzxcvzxcvzxcvzxcv"))
 	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	err = trie.TryDelete([]byte("123456"))
 	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
@@ -124,27 +125,27 @@ func testMissingNode(t *testing.T, memonly bool) {
 		diskdb.Delete(hash[:])
 	}
 
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	_, err = trie.TryGet([]byte("120000"))
 	if _, ok := err.(*MissingNodeError); !ok {
 		t.Errorf("Wrong error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	_, err = trie.TryGet([]byte("120099"))
 	if _, ok := err.(*MissingNodeError); !ok {
 		t.Errorf("Wrong error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	_, err = trie.TryGet([]byte("123456"))
 	if err != nil {
 		t.Errorf("Unexpected error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	err = trie.TryUpdate([]byte("120099"), []byte("zxcv"))
 	if _, ok := err.(*MissingNodeError); !ok {
 		t.Errorf("Wrong error: %v", err)
 	}
-	trie, _ = New(common.Hash{}, root, triedb)
+	trie, _ = New(TrieID(root), triedb)
 	err = trie.TryDelete([]byte("123456"))
 	if _, ok := err.(*MissingNodeError); !ok {
 		t.Errorf("Wrong error: %v", err)
@@ -198,7 +199,7 @@ func TestGet(t *testing.T) {
 		}
 		root, nodes, _ := trie.Commit(false)
 		db.Update(NewWithNodeSet(nodes))
-		trie, _ = New(common.Hash{}, root, db)
+		trie, _ = New(TrieID(root), db)
 	}
 }
 
@@ -275,7 +276,7 @@ func TestReplication(t *testing.T) {
 	triedb.Update(NewWithNodeSet(nodes))
 
 	// create a new trie on top of the database and check that lookups work.
-	trie2, err := New(common.Hash{}, exp, triedb)
+	trie2, err := New(TrieID(exp), triedb)
 	if err != nil {
 		t.Fatalf("can't recreate trie at %x: %v", exp, err)
 	}
@@ -296,7 +297,7 @@ func TestReplication(t *testing.T) {
 	if nodes != nil {
 		triedb.Update(NewWithNodeSet(nodes))
 	}
-	trie2, err = New(common.Hash{}, hash, triedb)
+	trie2, err = New(TrieID(hash), triedb)
 	if err != nil {
 		t.Fatalf("can't recreate trie at %x: %v", exp, err)
 	}
@@ -381,6 +382,7 @@ const (
 	opCommit
 	opItercheckhash
 	opNodeDiff
+	opProve
 	opMax // boundary value, not an actual op
 )
 
@@ -418,7 +420,7 @@ func generateSteps(finished func() bool, r io.Reader) randTest {
 			step.key = genKey()
 			step.value = make([]byte, 8)
 			binary.BigEndian.PutUint64(step.value, uint64(len(steps)))
-		case opGet, opDelete:
+		case opGet, opDelete, opProve:
 			step.key = genKey()
 		}
 		steps = append(steps, step)
@@ -456,24 +458,60 @@ func runRandTest(rt randTest) error {
 			if string(v) != want {
 				rt[i].err = fmt.Errorf("mismatch for key %#x, got %#x want %#x", step.key, v, want)
 			}
+		case opProve:
+			hash := tr.Hash()
+			if hash == types.EmptyRootHash {
+				continue
+			}
+			proofDb := rawdb.NewMemoryDatabase()
+			err := tr.Prove(step.key, 0, proofDb)
+			if err != nil {
+				rt[i].err = fmt.Errorf("failed for proving key %#x, %v", step.key, err)
+			}
+			_, err = VerifyProof(hash, step.key, proofDb)
+			if err != nil {
+				rt[i].err = fmt.Errorf("failed for verifying key %#x, %v", step.key, err)
+			}
 		case opHash:
 			tr.Hash()
 		case opCommit:
-			hash, nodes, err := tr.Commit(false)
+			root, nodes, err := tr.Commit(true)
 			if err != nil {
 				rt[i].err = err
 				return err
 			}
+			// Validity the returned nodeset
+			if nodes != nil {
+				for path, node := range nodes.updates.nodes {
+					blob, _, _ := origTrie.TryGetNode(hexToCompact([]byte(path)))
+					got := node.prev
+					if !bytes.Equal(blob, got) {
+						rt[i].err = fmt.Errorf("prevalue mismatch for 0x%x, got 0x%x want 0x%x", path, got, blob)
+						panic(rt[i].err)
+					}
+				}
+				for path, prev := range nodes.deletes {
+					blob, _, _ := origTrie.TryGetNode(hexToCompact([]byte(path)))
+					if !bytes.Equal(blob, prev) {
+						rt[i].err = fmt.Errorf("prevalue mismatch for 0x%x, got 0x%x want 0x%x", path, prev, blob)
+						panic(rt[i].err)
+					}
+				}
+			}
 			if nodes != nil {
 				triedb.Update(NewWithNodeSet(nodes))
 			}
-			newtr, err := New(common.Hash{}, hash, triedb)
+			newtr, err := New(TrieID(root), triedb)
 			if err != nil {
 				rt[i].err = err
 				return err
 			}
 			tr = newtr
+
+			// Enable node tracing. Resolve the root node again explicitly
+			// since it's not captured at the beginning.
 			tr.tracer = newTracer()
+			tr.resolveAndTrack(root.Bytes(), nil)
 
 			origTrie = tr.Copy()
 		case opItercheckhash:

trie/util_test.go

@@ -17,6 +17,7 @@
 package trie
 
 import (
+	"bytes"
 	"testing"
 
 	"github.com/XinFinOrg/XDPoSChain/common"
@@ -72,7 +73,7 @@ func TestTrieTracer(t *testing.T) {
 	if err := db.Update(NewWithNodeSet(nodes)); err != nil {
 		t.Fatal(err)
 	}
-	trie, _ = New(common.Hash{}, root, db)
+	trie, _ = New(TrieID(root), db)
 	trie.tracer = newTracer()
 
 	// Delete all the elements, check deletion set
@@ -124,3 +125,120 @@ func TestTrieTracerNoop(t *testing.T) {
 		t.Fatalf("Unexpected deleted node tracked %d", len(trie.tracer.deleteList()))
 	}
 }
+
+func TestTrieTracePrevValue(t *testing.T) {
+	db := NewDatabase(rawdb.NewMemoryDatabase())
+	trie := NewEmpty(db)
+	trie.tracer = newTracer()
+
+	paths, blobs := trie.tracer.prevList()
+	if len(paths) != 0 || len(blobs) != 0 {
+		t.Fatalf("Nothing should be tracked")
+	}
+	// Insert a batch of entries, all the nodes should be marked as inserted
+	vals := []struct{ k, v string }{
+		{"do", "verb"},
+		{"ether", "wookiedoo"},
+		{"horse", "stallion"},
+		{"shaman", "horse"},
+		{"doge", "coin"},
+		{"dog", "puppy"},
+		{"somethingveryoddindeedthis is", "myothernodedata"},
+	}
+	for _, val := range vals {
+		trie.Update([]byte(val.k), []byte(val.v))
+	}
+	paths, blobs = trie.tracer.prevList()
+	if len(paths) != 0 || len(blobs) != 0 {
+		t.Fatalf("Nothing should be tracked")
+	}
+
+	// Commit the changes and re-create with new root
+	root, nodes, _ := trie.Commit(false)
+	if err := db.Update(NewWithNodeSet(nodes)); err != nil {
+		t.Fatal(err)
+	}
+	trie, _ = New(TrieID(root), db)
+	trie.tracer = newTracer()
+	trie.resolveAndTrack(root.Bytes(), nil)
+
+	// Load all nodes in trie
+	for _, val := range vals {
+		trie.TryGet([]byte(val.k))
+	}
+
+	// Ensure all nodes are tracked by tracer with correct prev-values
+	iter := trie.NodeIterator(nil)
+	seen := make(map[string][]byte)
+	for iter.Next(true) {
+		// Embedded nodes are ignored since they are not present in
+		// database.
+		if iter.Hash() == (common.Hash{}) {
+			continue
+		}
+		seen[string(iter.Path())] = common.CopyBytes(iter.NodeBlob())
+	}
+
+	paths, blobs = trie.tracer.prevList()
+	if len(paths) != len(seen) || len(blobs) != len(seen) {
+		t.Fatalf("Unexpected tracked values")
+	}
+	for i, path := range paths {
+		blob := blobs[i]
+		prev, ok := seen[string(path)]
+		if !ok {
+			t.Fatalf("Missing node %v", path)
+		}
+		if !bytes.Equal(blob, prev) {
+			t.Fatalf("Unexpected value path: %v, want: %v, got: %v", path, prev, blob)
+		}
+	}
+
+	// Re-open the trie and iterate the trie, ensure nothing will be tracked.
+	// Iterator will not link any loaded nodes to trie.
+	trie, _ = New(TrieID(root), db)
+	trie.tracer = newTracer()
+
+	iter = trie.NodeIterator(nil)
+	for iter.Next(true) {
+	}
+	paths, blobs = trie.tracer.prevList()
+	if len(paths) != 0 || len(blobs) != 0 {
+		t.Fatalf("Nothing should be tracked")
+	}
+
+	// Re-open the trie and generate proof for entries, ensure nothing will
+	// be tracked. Prover will not link any loaded nodes to trie.
+	trie, _ = New(TrieID(root), db)
+	trie.tracer = newTracer()
+	for _, val := range vals {
+		trie.Prove([]byte(val.k), 0, rawdb.NewMemoryDatabase())
+	}
+	paths, blobs = trie.tracer.prevList()
+	if len(paths) != 0 || len(blobs) != 0 {
+		t.Fatalf("Nothing should be tracked")
+	}
+
+	// Delete entries from trie, ensure all previous values are correct.
+	trie, _ = New(TrieID(root), db)
+	trie.tracer = newTracer()
+	trie.resolveAndTrack(root.Bytes(), nil)
+
+	for _, val := range vals {
+		trie.TryDelete([]byte(val.k))
+	}
+	paths, blobs = trie.tracer.prevList()
+	if len(paths) != len(seen) || len(blobs) != len(seen) {
+		t.Fatalf("Unexpected tracked values")
+	}
+	for i, path := range paths {
+		blob := blobs[i]
+		prev, ok := seen[string(path)]
+		if !ok {
+			t.Fatalf("Missing node %v", path)
+		}
+		if !bytes.Equal(blob, prev) {
+			t.Fatalf("Unexpected value path: %v, want: %v, got: %v", path, prev, blob)
+		}
+	}
+}

trie/utils.go

@@ -50,45 +50,43 @@ func newTracer() *tracer {
 	}
 }
 
-/*
 // onRead tracks the newly loaded trie node and caches the rlp-encoded blob internally.
 // Don't change the value outside of function since it's not deep-copied.
-func (t *tracer) onRead(key []byte, val []byte) {
+func (t *tracer) onRead(path []byte, val []byte) {
 	// Tracer isn't used right now, remove this check later.
 	if t == nil {
 		return
 	}
-	t.origin[string(key)] = val
+	t.origin[string(path)] = val
 }
-*/
 
 // onInsert tracks the newly inserted trie node. If it's already in the deletion set
 // (resurrected node), then just wipe it from the deletion set as the "untouched".
-func (t *tracer) onInsert(key []byte) {
+func (t *tracer) onInsert(path []byte) {
 	// Tracer isn't used right now, remove this check later.
 	if t == nil {
 		return
 	}
-	if _, present := t.delete[string(key)]; present {
+	if _, present := t.delete[string(path)]; present {
-		delete(t.delete, string(key))
+		delete(t.delete, string(path))
 		return
 	}
-	t.insert[string(key)] = struct{}{}
+	t.insert[string(path)] = struct{}{}
 }
 
 // onDelete tracks the newly deleted trie node. If it's already
 // in the addition set, then just wipe it from the addition set
 // as it's untouched.
-func (t *tracer) onDelete(key []byte) {
+func (t *tracer) onDelete(path []byte) {
 	// Tracer isn't used right now, remove this check later.
 	if t == nil {
 		return
 	}
-	if _, present := t.insert[string(key)]; present {
+	if _, present := t.insert[string(path)]; present {
-		delete(t.insert, string(key))
+		delete(t.insert, string(path))
 		return
 	}
-	t.delete[string(key)] = struct{}{}
+	t.delete[string(path)] = struct{}{}
 }
 
 // insertList returns the tracked inserted trie nodes in list format.
@@ -98,8 +96,8 @@ func (t *tracer) insertList() [][]byte {
 		return nil
 	}
 	var ret [][]byte
-	for key := range t.insert {
+	for path := range t.insert {
-		ret = append(ret, []byte(key))
+		ret = append(ret, []byte(path))
 	}
 	return ret
 }
@@ -111,22 +109,37 @@ func (t *tracer) deleteList() [][]byte {
 		return nil
 	}
 	var ret [][]byte
-	for key := range t.delete {
+	for path := range t.delete {
-		ret = append(ret, []byte(key))
+		ret = append(ret, []byte(path))
 	}
 	return ret
 }
 
-/*
+// prevList returns the tracked node blobs in list format.
+func (t *tracer) prevList() ([][]byte, [][]byte) {
+	// Tracer isn't used right now, remove this check later.
+	if t == nil {
+		return nil, nil
+	}
+	var (
+		paths [][]byte
+		blobs [][]byte
+	)
+	for path, blob := range t.origin {
+		paths = append(paths, []byte(path))
+		blobs = append(blobs, blob)
+	}
+	return paths, blobs
+}
+
 // getPrev returns the cached original value of the specified node.
-func (t *tracer) getPrev(key []byte) []byte {
+func (t *tracer) getPrev(path []byte) []byte {
-	// Don't panic on uninitialized tracer, it's possible in testing.
+	// Tracer isn't used right now, remove this check later.
 	if t == nil {
 		return nil
 	}
-	return t.origin[string(key)]
+	return t.origin[string(path)]
 }
-*/
 
 // reset clears the content tracked by tracer.
 func (t *tracer) reset() {