core/state: access trie through Database interface, track errors (#14589)

With this commit, core/state's access to the underlying key/value database is
mediated through an interface. Database errors are tracked in StateDB and
returned by CommitTo or the new Error method.

Motivation for this change: We can remove the light client's duplicated copy of
core/state. The light client now supports node iteration, so tracing and storage
enumeration can work with the light client (not implemented in this commit).

10 files changed, 312 insertions, 216 deletions

diff --git a/core/state/database.go b/core/state/database.go
new file mode 100644
index 000000000..946625e76
--- /dev/null
+++ b/core/state/database.go
@@ -0,0 +1,154 @@
+// Copyright 2017 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 state
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/trie"
+	lru "github.com/hashicorp/golang-lru"
+)
+
+// Trie cache generation limit after which to evic trie nodes from memory.
+var MaxTrieCacheGen = uint16(120)
+
+const (
+	// Number of past tries to keep. This value is chosen such that
+	// reasonable chain reorg depths will hit an existing trie.
+	maxPastTries = 12
+
+	// Number of codehash->size associations to keep.
+	codeSizeCacheSize = 100000
+)
+
+// Database wraps access to tries and contract code.
+type Database interface {
+	// Accessing tries:
+	// OpenTrie opens the main account trie.
+	// OpenStorageTrie opens the storage trie of an account.
+	OpenTrie(root common.Hash) (Trie, error)
+	OpenStorageTrie(addrHash, root common.Hash) (Trie, error)
+	// Accessing contract code:
+	ContractCode(addrHash, codeHash common.Hash) ([]byte, error)
+	ContractCodeSize(addrHash, codeHash common.Hash) (int, error)
+	// CopyTrie returns an independent copy of the given trie.
+	CopyTrie(Trie) Trie
+}
+
+// Trie is a Ethereum Merkle Trie.
+type Trie interface {
+	TryGet(key []byte) ([]byte, error)
+	TryUpdate(key, value []byte) error
+	TryDelete(key []byte) error
+	CommitTo(trie.DatabaseWriter) (common.Hash, error)
+	Hash() common.Hash
+	NodeIterator(startKey []byte) trie.NodeIterator
+	GetKey([]byte) []byte // TODO(fjl): remove this when SecureTrie is removed
+}
+
+// NewDatabase creates a backing store for state. The returned database is safe for
+// concurrent use and retains cached trie nodes in memory.
+func NewDatabase(db ethdb.Database) Database {
+	csc, _ := lru.New(codeSizeCacheSize)
+	return &cachingDB{db: db, codeSizeCache: csc}
+}
+
+type cachingDB struct {
+	db            ethdb.Database
+	mu            sync.Mutex
+	pastTries     []*trie.SecureTrie
+	codeSizeCache *lru.Cache
+}
+
+func (db *cachingDB) OpenTrie(root common.Hash) (Trie, error) {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+
+	for i := len(db.pastTries) - 1; i >= 0; i-- {
+		if db.pastTries[i].Hash() == root {
+			return cachedTrie{db.pastTries[i].Copy(), db}, nil
+		}
+	}
+	tr, err := trie.NewSecure(root, db.db, MaxTrieCacheGen)
+	if err != nil {
+		return nil, err
+	}
+	return cachedTrie{tr, db}, nil
+}
+
+func (db *cachingDB) pushTrie(t *trie.SecureTrie) {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+
+	if len(db.pastTries) >= maxPastTries {
+		copy(db.pastTries, db.pastTries[1:])
+		db.pastTries[len(db.pastTries)-1] = t
+	} else {
+		db.pastTries = append(db.pastTries, t)
+	}
+}
+
+func (db *cachingDB) OpenStorageTrie(addrHash, root common.Hash) (Trie, error) {
+	return trie.NewSecure(root, db.db, 0)
+}
+
+func (db *cachingDB) CopyTrie(t Trie) Trie {
+	switch t := t.(type) {
+	case cachedTrie:
+		return cachedTrie{t.SecureTrie.Copy(), db}
+	case *trie.SecureTrie:
+		return t.Copy()
+	default:
+		panic(fmt.Errorf("unknown trie type %T", t))
+	}
+}
+
+func (db *cachingDB) ContractCode(addrHash, codeHash common.Hash) ([]byte, error) {
+	code, err := db.db.Get(codeHash[:])
+	if err == nil {
+		db.codeSizeCache.Add(codeHash, len(code))
+	}
+	return code, err
+}
+
+func (db *cachingDB) ContractCodeSize(addrHash, codeHash common.Hash) (int, error) {
+	if cached, ok := db.codeSizeCache.Get(codeHash); ok {
+		return cached.(int), nil
+	}
+	code, err := db.ContractCode(addrHash, codeHash)
+	if err == nil {
+		db.codeSizeCache.Add(codeHash, len(code))
+	}
+	return len(code), err
+}
+
+// cachedTrie inserts its trie into a cachingDB on commit.
+type cachedTrie struct {
+	*trie.SecureTrie
+	db *cachingDB
+}
+
+func (m cachedTrie) CommitTo(dbw trie.DatabaseWriter) (common.Hash, error) {
+	root, err := m.SecureTrie.CommitTo(dbw)
+	if err == nil {
+		m.db.pushTrie(m.SecureTrie)
+	}
+	return root, err
+}
diff --git a/core/state/dump.go b/core/state/dump.go
index ffa1a7283..46e612850 100644
--- a/core/state/dump.go
+++ b/core/state/dump.go
@@ -41,7 +41,7 @@ type Dump struct {
 
 func (self *StateDB) RawDump() Dump {
 	dump := Dump{
-		Root:     common.Bytes2Hex(self.trie.Root()),
+		Root:     fmt.Sprintf("%x", self.trie.Hash()),
 		Accounts: make(map[string]DumpAccount),
 	}
 
diff --git a/core/state/iterator.go b/core/state/iterator.go
index a8a2722ae..6a5c73d3d 100644
--- a/core/state/iterator.go
+++ b/core/state/iterator.go
@@ -19,7 +19,6 @@ package state
 import (
 	"bytes"
 	"fmt"
-	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/rlp"
@@ -105,16 +104,11 @@ func (it *NodeIterator) step() error {
 		return nil
 	}
 	// Otherwise we've reached an account node, initiate data iteration
-	var account struct {
-		Nonce    uint64
-		Balance  *big.Int
-		Root     common.Hash
-		CodeHash []byte
-	}
+	var account Account
 	if err := rlp.Decode(bytes.NewReader(it.stateIt.LeafBlob()), &account); err != nil {
 		return err
 	}
-	dataTrie, err := trie.New(account.Root, it.state.db)
+	dataTrie, err := it.state.db.OpenStorageTrie(common.BytesToHash(it.stateIt.LeafKey()), account.Root)
 	if err != nil {
 		return err
 	}
@@ -124,7 +118,8 @@ func (it *NodeIterator) step() error {
 	}
 	if !bytes.Equal(account.CodeHash, emptyCodeHash) {
 		it.codeHash = common.BytesToHash(account.CodeHash)
-		it.code, err = it.state.db.Get(account.CodeHash)
+		addrHash := common.BytesToHash(it.stateIt.LeafKey())
+		it.code, err = it.state.db.ContractCode(addrHash, common.BytesToHash(account.CodeHash))
 		if err != nil {
 			return fmt.Errorf("code %x: %v", account.CodeHash, err)
 		}
diff --git a/core/state/iterator_test.go b/core/state/iterator_test.go
index aa9c5b728..ff66ba7a9 100644
--- a/core/state/iterator_test.go
+++ b/core/state/iterator_test.go
@@ -21,13 +21,12 @@ import (
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/ethdb"
 )
 
 // Tests that the node iterator indeed walks over the entire database contents.
 func TestNodeIteratorCoverage(t *testing.T) {
 	// Create some arbitrary test state to iterate
-	db, root, _ := makeTestState()
+	db, mem, root, _ := makeTestState()
 
 	state, err := New(root, db)
 	if err != nil {
@@ -40,13 +39,14 @@ func TestNodeIteratorCoverage(t *testing.T) {
 			hashes[it.Hash] = struct{}{}
 		}
 	}
+
 	// Cross check the hashes and the database itself
 	for hash := range hashes {
-		if _, err := db.Get(hash.Bytes()); err != nil {
+		if _, err := mem.Get(hash.Bytes()); err != nil {
 			t.Errorf("failed to retrieve reported node %x: %v", hash, err)
 		}
 	}
-	for _, key := range db.(*ethdb.MemDatabase).Keys() {
+	for _, key := range mem.Keys() {
 		if bytes.HasPrefix(key, []byte("secure-key-")) {
 			continue
 		}
diff --git a/core/state/managed_state_test.go b/core/state/managed_state_test.go
index ea5737a08..1cfdd3a89 100644
--- a/core/state/managed_state_test.go
+++ b/core/state/managed_state_test.go
@@ -27,7 +27,7 @@ var addr = common.BytesToAddress([]byte("test"))
 
 func create() (*ManagedState, *account) {
 	db, _ := ethdb.NewMemDatabase()
-	statedb, _ := New(common.Hash{}, db)
+	statedb, _ := New(common.Hash{}, NewDatabase(db))
 	ms := ManageState(statedb)
 	ms.StateDB.SetNonce(addr, 100)
 	ms.accounts[addr] = newAccount(ms.StateDB.getStateObject(addr))
diff --git a/core/state/state_object.go b/core/state/state_object.go
index dcad9d068..b2378c69c 100644
--- a/core/state/state_object.go
+++ b/core/state/state_object.go
@@ -62,9 +62,10 @@ func (self Storage) Copy() Storage {
 // Account values can be accessed and modified through the object.
 // Finally, call CommitTrie to write the modified storage trie into a database.
 type stateObject struct {
-	address common.Address // Ethereum address of this account
-	data    Account
-	db      *StateDB
+	address  common.Address
+	addrHash common.Hash // hash of ethereum address of the account
+	data     Account
+	db       *StateDB
 
 	// DB error.
 	// State objects are used by the consensus core and VM which are
@@ -74,8 +75,8 @@ type stateObject struct {
 	dbErr error
 
 	// Write caches.
-	trie *trie.SecureTrie // storage trie, which becomes non-nil on first access
-	code Code             // contract bytecode, which gets set when code is loaded
+	trie Trie // storage trie, which becomes non-nil on first access
+	code Code // contract bytecode, which gets set when code is loaded
 
 	cachedStorage Storage // Storage entry cache to avoid duplicate reads
 	dirtyStorage  Storage // Storage entries that need to be flushed to disk
@@ -112,7 +113,15 @@ func newObject(db *StateDB, address common.Address, data Account, onDirty func(a
 	if data.CodeHash == nil {
 		data.CodeHash = emptyCodeHash
 	}
-	return &stateObject{db: db, address: address, data: data, cachedStorage: make(Storage), dirtyStorage: make(Storage), onDirty: onDirty}
+	return &stateObject{
+		db:            db,
+		address:       address,
+		addrHash:      crypto.Keccak256Hash(address[:]),
+		data:          data,
+		cachedStorage: make(Storage),
+		dirtyStorage:  make(Storage),
+		onDirty:       onDirty,
+	}
 }
 
 // EncodeRLP implements rlp.Encoder.
@@ -148,12 +157,12 @@ func (c *stateObject) touch() {
 	c.touched = true
 }
 
-func (c *stateObject) getTrie(db trie.Database) *trie.SecureTrie {
+func (c *stateObject) getTrie(db Database) Trie {
 	if c.trie == nil {
 		var err error
-		c.trie, err = trie.NewSecure(c.data.Root, db, 0)
+		c.trie, err = db.OpenStorageTrie(c.addrHash, c.data.Root)
 		if err != nil {
-			c.trie, _ = trie.NewSecure(common.Hash{}, db, 0)
+			c.trie, _ = db.OpenStorageTrie(c.addrHash, common.Hash{})
 			c.setError(fmt.Errorf("can't create storage trie: %v", err))
 		}
 	}
@@ -161,13 +170,18 @@ func (c *stateObject) getTrie(db trie.Database) *trie.SecureTrie {
 }
 
 // GetState returns a value in account storage.
-func (self *stateObject) GetState(db trie.Database, key common.Hash) common.Hash {
+func (self *stateObject) GetState(db Database, key common.Hash) common.Hash {
 	value, exists := self.cachedStorage[key]
 	if exists {
 		return value
 	}
 	// Load from DB in case it is missing.
-	if enc := self.getTrie(db).Get(key[:]); len(enc) > 0 {
+	enc, err := self.getTrie(db).TryGet(key[:])
+	if err != nil {
+		self.setError(err)
+		return common.Hash{}
+	}
+	if len(enc) > 0 {
 		_, content, _, err := rlp.Split(enc)
 		if err != nil {
 			self.setError(err)
@@ -181,7 +195,7 @@ func (self *stateObject) GetState(db trie.Database, key common.Hash) common.Hash
 }
 
 // SetState updates a value in account storage.
-func (self *stateObject) SetState(db trie.Database, key, value common.Hash) {
+func (self *stateObject) SetState(db Database, key, value common.Hash) {
 	self.db.journal = append(self.db.journal, storageChange{
 		account:  &self.address,
 		key:      key,
@@ -201,30 +215,30 @@ func (self *stateObject) setState(key, value common.Hash) {
 }
 
 // updateTrie writes cached storage modifications into the object's storage trie.
-func (self *stateObject) updateTrie(db trie.Database) *trie.SecureTrie {
+func (self *stateObject) updateTrie(db Database) Trie {
 	tr := self.getTrie(db)
 	for key, value := range self.dirtyStorage {
 		delete(self.dirtyStorage, key)
 		if (value == common.Hash{}) {
-			tr.Delete(key[:])
+			self.setError(tr.TryDelete(key[:]))
 			continue
 		}
 		// Encoding []byte cannot fail, ok to ignore the error.
 		v, _ := rlp.EncodeToBytes(bytes.TrimLeft(value[:], "\x00"))
-		tr.Update(key[:], v)
+		self.setError(tr.TryUpdate(key[:], v))
 	}
 	return tr
 }
 
 // UpdateRoot sets the trie root to the current root hash of
-func (self *stateObject) updateRoot(db trie.Database) {
+func (self *stateObject) updateRoot(db Database) {
 	self.updateTrie(db)
 	self.data.Root = self.trie.Hash()
 }
 
 // CommitTrie the storage trie of the object to dwb.
 // This updates the trie root.
-func (self *stateObject) CommitTrie(db trie.Database, dbw trie.DatabaseWriter) error {
+func (self *stateObject) CommitTrie(db Database, dbw trie.DatabaseWriter) error {
 	self.updateTrie(db)
 	if self.dbErr != nil {
 		return self.dbErr
@@ -282,9 +296,7 @@ func (c *stateObject) ReturnGas(gas *big.Int) {}
 func (self *stateObject) deepCopy(db *StateDB, onDirty func(addr common.Address)) *stateObject {
 	stateObject := newObject(db, self.address, self.data, onDirty)
 	if self.trie != nil {
-		// A shallow copy makes the two tries independent.
-		cpy := *self.trie
-		stateObject.trie = &cpy
+		stateObject.trie = db.db.CopyTrie(self.trie)
 	}
 	stateObject.code = self.code
 	stateObject.dirtyStorage = self.dirtyStorage.Copy()
@@ -305,14 +317,14 @@ func (c *stateObject) Address() common.Address {
 }
 
 // Code returns the contract code associated with this object, if any.
-func (self *stateObject) Code(db trie.Database) []byte {
+func (self *stateObject) Code(db Database) []byte {
 	if self.code != nil {
 		return self.code
 	}
 	if bytes.Equal(self.CodeHash(), emptyCodeHash) {
 		return nil
 	}
-	code, err := db.Get(self.CodeHash())
+	code, err := db.ContractCode(self.addrHash, common.BytesToHash(self.CodeHash()))
 	if err != nil {
 		self.setError(fmt.Errorf("can't load code hash %x: %v", self.CodeHash(), err))
 	}
diff --git a/core/state/state_test.go b/core/state/state_test.go
index 3bc63c148..bbae3685b 100644
--- a/core/state/state_test.go
+++ b/core/state/state_test.go
@@ -21,14 +21,14 @@ import (
 	"math/big"
 	"testing"
 
-	checker "gopkg.in/check.v1"
-
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/ethdb"
+	checker "gopkg.in/check.v1"
 )
 
 type StateSuite struct {
+	db    *ethdb.MemDatabase
 	state *StateDB
 }
 
@@ -48,7 +48,7 @@ func (s *StateSuite) TestDump(c *checker.C) {
 	// write some of them to the trie
 	s.state.updateStateObject(obj1)
 	s.state.updateStateObject(obj2)
-	s.state.Commit(false)
+	s.state.CommitTo(s.db, false)
 
 	// check that dump contains the state objects that are in trie
 	got := string(s.state.Dump())
@@ -87,23 +87,20 @@ func (s *StateSuite) TestDump(c *checker.C) {
 }
 
 func (s *StateSuite) SetUpTest(c *checker.C) {
-	db, _ := ethdb.NewMemDatabase()
-	s.state, _ = New(common.Hash{}, db)
+	s.db, _ = ethdb.NewMemDatabase()
+	s.state, _ = New(common.Hash{}, NewDatabase(s.db))
 }
 
-func TestNull(t *testing.T) {
-	db, _ := ethdb.NewMemDatabase()
-	state, _ := New(common.Hash{}, db)
-
+func (s *StateSuite) TestNull(c *checker.C) {
 	address := common.HexToAddress("0x823140710bf13990e4500136726d8b55")
-	state.CreateAccount(address)
+	s.state.CreateAccount(address)
 	//value := common.FromHex("0x823140710bf13990e4500136726d8b55")
 	var value common.Hash
-	state.SetState(address, common.Hash{}, value)
-	state.Commit(false)
-	value = state.GetState(address, common.Hash{})
+	s.state.SetState(address, common.Hash{}, value)
+	s.state.CommitTo(s.db, false)
+	value = s.state.GetState(address, common.Hash{})
 	if !common.EmptyHash(value) {
-		t.Errorf("expected empty hash. got %x", value)
+		c.Errorf("expected empty hash. got %x", value)
 	}
 }
 
@@ -129,17 +126,15 @@ func (s *StateSuite) TestSnapshot(c *checker.C) {
 	c.Assert(data1, checker.DeepEquals, res)
 }
 
-func TestSnapshotEmpty(t *testing.T) {
-	db, _ := ethdb.NewMemDatabase()
-	state, _ := New(common.Hash{}, db)
-	state.RevertToSnapshot(state.Snapshot())
+func (s *StateSuite) TestSnapshotEmpty(c *checker.C) {
+	s.state.RevertToSnapshot(s.state.Snapshot())
 }
 
 // use testing instead of checker because checker does not support
 // printing/logging in tests (-check.vv does not work)
 func TestSnapshot2(t *testing.T) {
 	db, _ := ethdb.NewMemDatabase()
-	state, _ := New(common.Hash{}, db)
+	state, _ := New(common.Hash{}, NewDatabase(db))
 
 	stateobjaddr0 := toAddr([]byte("so0"))
 	stateobjaddr1 := toAddr([]byte("so1"))
@@ -160,7 +155,7 @@ func TestSnapshot2(t *testing.T) {
 	so0.deleted = false
 	state.setStateObject(so0)
 
-	root, _ := state.Commit(false)
+	root, _ := state.CommitTo(db, false)
 	state.Reset(root)
 
 	// and one with deleted == true
@@ -182,8 +177,8 @@ func TestSnapshot2(t *testing.T) {
 
 	so0Restored := state.getStateObject(stateobjaddr0)
 	// Update lazily-loaded values before comparing.
-	so0Restored.GetState(db, storageaddr)
-	so0Restored.Code(db)
+	so0Restored.GetState(state.db, storageaddr)
+	so0Restored.Code(state.db)
 	// non-deleted is equal (restored)
 	compareStateObjects(so0Restored, so0, t)
 
diff --git a/core/state/statedb.go b/core/state/statedb.go
index 05869a0c8..694374f82 100644
--- a/core/state/statedb.go
+++ b/core/state/statedb.go
@@ -26,23 +26,9 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto"
-	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/trie"
-	lru "github.com/hashicorp/golang-lru"
-)
-
-// Trie cache generation limit after which to evic trie nodes from memory.
-var MaxTrieCacheGen = uint16(120)
-
-const (
-	// Number of past tries to keep. This value is chosen such that
-	// reasonable chain reorg depths will hit an existing trie.
-	maxPastTries = 12
-
-	// Number of codehash->size associations to keep.
-	codeSizeCacheSize = 100000
 )
 
 type revision struct {
@@ -56,16 +42,21 @@ type revision struct {
 // * Contracts
 // * Accounts
 type StateDB struct {
-	db            ethdb.Database
-	trie          *trie.SecureTrie
-	pastTries     []*trie.SecureTrie
-	codeSizeCache *lru.Cache
+	db   Database
+	trie Trie
 
 	// This map holds 'live' objects, which will get modified while processing a state transition.
 	stateObjects           map[common.Address]*stateObject
 	stateObjectsDirty      map[common.Address]struct{}
 	stateObjectsDestructed map[common.Address]struct{}
 
+	// DB error.
+	// State objects are used by the consensus core and VM which are
+	// unable to deal with database-level errors. Any error that occurs
+	// during a database read is memoized here and will eventually be returned
+	// by StateDB.Commit.
+	dbErr error
+
 	// The refund counter, also used by state transitioning.
 	refund *big.Int
 
@@ -86,16 +77,14 @@ type StateDB struct {
 }
 
 // Create a new state from a given trie
-func New(root common.Hash, db ethdb.Database) (*StateDB, error) {
-	tr, err := trie.NewSecure(root, db, MaxTrieCacheGen)
+func New(root common.Hash, db Database) (*StateDB, error) {
+	tr, err := db.OpenTrie(root)
 	if err != nil {
 		return nil, err
 	}
-	csc, _ := lru.New(codeSizeCacheSize)
 	return &StateDB{
 		db:                     db,
 		trie:                   tr,
-		codeSizeCache:          csc,
 		stateObjects:           make(map[common.Address]*stateObject),
 		stateObjectsDirty:      make(map[common.Address]struct{}),
 		stateObjectsDestructed: make(map[common.Address]struct{}),
@@ -105,36 +94,21 @@ func New(root common.Hash, db ethdb.Database) (*StateDB, error) {
 	}, nil
 }
 
-// New creates a new statedb by reusing any journalled tries to avoid costly
-// disk io.
-func (self *StateDB) New(root common.Hash) (*StateDB, error) {
-	self.lock.Lock()
-	defer self.lock.Unlock()
-
-	tr, err := self.openTrie(root)
-	if err != nil {
-		return nil, err
+// setError remembers the first non-nil error it is called with.
+func (self *StateDB) setError(err error) {
+	if self.dbErr == nil {
+		self.dbErr = err
 	}
-	return &StateDB{
-		db:                     self.db,
-		trie:                   tr,
-		codeSizeCache:          self.codeSizeCache,
-		stateObjects:           make(map[common.Address]*stateObject),
-		stateObjectsDirty:      make(map[common.Address]struct{}),
-		stateObjectsDestructed: make(map[common.Address]struct{}),
-		refund:                 new(big.Int),
-		logs:                   make(map[common.Hash][]*types.Log),
-		preimages:              make(map[common.Hash][]byte),
-	}, nil
+}
+
+func (self *StateDB) Error() error {
+	return self.dbErr
 }
 
 // Reset clears out all emphemeral state objects from the state db, but keeps
 // the underlying state trie to avoid reloading data for the next operations.
 func (self *StateDB) Reset(root common.Hash) error {
-	self.lock.Lock()
-	defer self.lock.Unlock()
-
-	tr, err := self.openTrie(root)
+	tr, err := self.db.OpenTrie(root)
 	if err != nil {
 		return err
 	}
@@ -149,34 +123,9 @@ func (self *StateDB) Reset(root common.Hash) error {
 	self.logSize = 0
 	self.preimages = make(map[common.Hash][]byte)
 	self.clearJournalAndRefund()
-
 	return nil
 }
 
-// openTrie creates a trie. It uses an existing trie if one is available
-// from the journal if available.
-func (self *StateDB) openTrie(root common.Hash) (*trie.SecureTrie, error) {
-	for i := len(self.pastTries) - 1; i >= 0; i-- {
-		if self.pastTries[i].Hash() == root {
-			tr := *self.pastTries[i]
-			return &tr, nil
-		}
-	}
-	return trie.NewSecure(root, self.db, MaxTrieCacheGen)
-}
-
-func (self *StateDB) pushTrie(t *trie.SecureTrie) {
-	self.lock.Lock()
-	defer self.lock.Unlock()
-
-	if len(self.pastTries) >= maxPastTries {
-		copy(self.pastTries, self.pastTries[1:])
-		self.pastTries[len(self.pastTries)-1] = t
-	} else {
-		self.pastTries = append(self.pastTries, t)
-	}
-}
-
 func (self *StateDB) AddLog(log *types.Log) {
 	self.journal = append(self.journal, addLogChange{txhash: self.thash})
 
@@ -254,10 +203,7 @@ func (self *StateDB) GetNonce(addr common.Address) uint64 {
 func (self *StateDB) GetCode(addr common.Address) []byte {
 	stateObject := self.getStateObject(addr)
 	if stateObject != nil {
-		code := stateObject.Code(self.db)
-		key := common.BytesToHash(stateObject.CodeHash())
-		self.codeSizeCache.Add(key, len(code))
-		return code
+		return stateObject.Code(self.db)
 	}
 	return nil
 }
@@ -267,13 +213,12 @@ func (self *StateDB) GetCodeSize(addr common.Address) int {
 	if stateObject == nil {
 		return 0
 	}
-	key := common.BytesToHash(stateObject.CodeHash())
-	if cached, ok := self.codeSizeCache.Get(key); ok {
-		return cached.(int)
+	if stateObject.code != nil {
+		return len(stateObject.code)
 	}
-	size := len(stateObject.Code(self.db))
-	if stateObject.dbErr == nil {
-		self.codeSizeCache.Add(key, size)
+	size, err := self.db.ContractCodeSize(stateObject.addrHash, common.BytesToHash(stateObject.CodeHash()))
+	if err != nil {
+		self.setError(err)
 	}
 	return size
 }
@@ -296,7 +241,7 @@ func (self *StateDB) GetState(a common.Address, b common.Hash) common.Hash {
 
 // StorageTrie returns the storage trie of an account.
 // The return value is a copy and is nil for non-existent accounts.
-func (self *StateDB) StorageTrie(a common.Address) *trie.SecureTrie {
+func (self *StateDB) StorageTrie(a common.Address) Trie {
 	stateObject := self.getStateObject(a)
 	if stateObject == nil {
 		return nil
@@ -394,14 +339,14 @@ func (self *StateDB) updateStateObject(stateObject *stateObject) {
 	if err != nil {
 		panic(fmt.Errorf("can't encode object at %x: %v", addr[:], err))
 	}
-	self.trie.Update(addr[:], data)
+	self.setError(self.trie.TryUpdate(addr[:], data))
 }
 
 // deleteStateObject removes the given object from the state trie.
 func (self *StateDB) deleteStateObject(stateObject *stateObject) {
 	stateObject.deleted = true
 	addr := stateObject.Address()
-	self.trie.Delete(addr[:])
+	self.setError(self.trie.TryDelete(addr[:]))
 }
 
 // Retrieve a state object given my the address. Returns nil if not found.
@@ -415,8 +360,9 @@ func (self *StateDB) getStateObject(addr common.Address) (stateObject *stateObje
 	}
 
 	// Load the object from the database.
-	enc := self.trie.Get(addr[:])
+	enc, err := self.trie.TryGet(addr[:])
 	if len(enc) == 0 {
+		self.setError(err)
 		return nil
 	}
 	var data Account
@@ -512,8 +458,6 @@ func (self *StateDB) Copy() *StateDB {
 	state := &StateDB{
 		db:                     self.db,
 		trie:                   self.trie,
-		pastTries:              self.pastTries,
-		codeSizeCache:          self.codeSizeCache,
 		stateObjects:           make(map[common.Address]*stateObject, len(self.stateObjectsDirty)),
 		stateObjectsDirty:      make(map[common.Address]struct{}, len(self.stateObjectsDirty)),
 		stateObjectsDestructed: make(map[common.Address]struct{}, len(self.stateObjectsDestructed)),
@@ -636,23 +580,6 @@ func (s *StateDB) DeleteSuicides() {
 	}
 }
 
-// Commit commits all state changes to the database.
-func (s *StateDB) Commit(deleteEmptyObjects bool) (root common.Hash, err error) {
-	root, batch := s.CommitBatch(deleteEmptyObjects)
-	return root, batch.Write()
-}
-
-// CommitBatch commits all state changes to a write batch but does not
-// execute the batch. It is used to validate state changes against
-// the root hash stored in a block.
-func (s *StateDB) CommitBatch(deleteEmptyObjects bool) (root common.Hash, batch ethdb.Batch) {
-	batch = s.db.NewBatch()
-	root, _ = s.CommitTo(batch, deleteEmptyObjects)
-
-	log.Debug("Trie cache stats after commit", "misses", trie.CacheMisses(), "unloads", trie.CacheUnloads())
-	return root, batch
-}
-
 func (s *StateDB) clearJournalAndRefund() {
 	s.journal = nil
 	s.validRevisions = s.validRevisions[:0]
@@ -690,8 +617,6 @@ func (s *StateDB) CommitTo(dbw trie.DatabaseWriter, deleteEmptyObjects bool) (ro
 	}
 	// Write trie changes.
 	root, err = s.trie.CommitTo(dbw)
-	if err == nil {
-		s.pushTrie(s.trie)
-	}
+	log.Debug("Trie cache stats after commit", "misses", trie.CacheMisses(), "unloads", trie.CacheUnloads())
 	return root, err
 }
diff --git a/core/state/statedb_test.go b/core/state/statedb_test.go
index 72b638f97..b2bd18e65 100644
--- a/core/state/statedb_test.go
+++ b/core/state/statedb_test.go
@@ -28,6 +28,8 @@ import (
 	"testing"
 	"testing/quick"
 
+	check "gopkg.in/check.v1"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/ethdb"
@@ -38,7 +40,7 @@ import (
 func TestUpdateLeaks(t *testing.T) {
 	// Create an empty state database
 	db, _ := ethdb.NewMemDatabase()
-	state, _ := New(common.Hash{}, db)
+	state, _ := New(common.Hash{}, NewDatabase(db))
 
 	// Update it with some accounts
 	for i := byte(0); i < 255; i++ {
@@ -66,8 +68,8 @@ func TestIntermediateLeaks(t *testing.T) {
 	// Create two state databases, one transitioning to the final state, the other final from the beginning
 	transDb, _ := ethdb.NewMemDatabase()
 	finalDb, _ := ethdb.NewMemDatabase()
-	transState, _ := New(common.Hash{}, transDb)
-	finalState, _ := New(common.Hash{}, finalDb)
+	transState, _ := New(common.Hash{}, NewDatabase(transDb))
+	finalState, _ := New(common.Hash{}, NewDatabase(finalDb))
 
 	modify := func(state *StateDB, addr common.Address, i, tweak byte) {
 		state.SetBalance(addr, big.NewInt(int64(11*i)+int64(tweak)))
@@ -95,10 +97,10 @@ func TestIntermediateLeaks(t *testing.T) {
 	}
 
 	// Commit and cross check the databases.
-	if _, err := transState.Commit(false); err != nil {
+	if _, err := transState.CommitTo(transDb, false); err != nil {
 		t.Fatalf("failed to commit transition state: %v", err)
 	}
-	if _, err := finalState.Commit(false); err != nil {
+	if _, err := finalState.CommitTo(finalDb, false); err != nil {
 		t.Fatalf("failed to commit final state: %v", err)
 	}
 	for _, key := range finalDb.Keys() {
@@ -282,7 +284,7 @@ func (test *snapshotTest) run() bool {
 	// Run all actions and create snapshots.
 	var (
 		db, _        = ethdb.NewMemDatabase()
-		state, _     = New(common.Hash{}, db)
+		state, _     = New(common.Hash{}, NewDatabase(db))
 		snapshotRevs = make([]int, len(test.snapshots))
 		sindex       = 0
 	)
@@ -297,7 +299,7 @@ func (test *snapshotTest) run() bool {
 	// Revert all snapshots in reverse order. Each revert must yield a state
 	// that is equivalent to fresh state with all actions up the snapshot applied.
 	for sindex--; sindex >= 0; sindex-- {
-		checkstate, _ := New(common.Hash{}, db)
+		checkstate, _ := New(common.Hash{}, NewDatabase(db))
 		for _, action := range test.actions[:test.snapshots[sindex]] {
 			action.fn(action, checkstate)
 		}
@@ -354,21 +356,19 @@ func (test *snapshotTest) checkEqual(state, checkstate *StateDB) error {
 	return nil
 }
 
-func TestTouchDelete(t *testing.T) {
-	db, _ := ethdb.NewMemDatabase()
-	state, _ := New(common.Hash{}, db)
-	state.GetOrNewStateObject(common.Address{})
-	root, _ := state.Commit(false)
-	state.Reset(root)
+func (s *StateSuite) TestTouchDelete(c *check.C) {
+	s.state.GetOrNewStateObject(common.Address{})
+	root, _ := s.state.CommitTo(s.db, false)
+	s.state.Reset(root)
 
-	snapshot := state.Snapshot()
-	state.AddBalance(common.Address{}, new(big.Int))
-	if len(state.stateObjectsDirty) != 1 {
-		t.Fatal("expected one dirty state object")
+	snapshot := s.state.Snapshot()
+	s.state.AddBalance(common.Address{}, new(big.Int))
+	if len(s.state.stateObjectsDirty) != 1 {
+		c.Fatal("expected one dirty state object")
 	}
 
-	state.RevertToSnapshot(snapshot)
-	if len(state.stateObjectsDirty) != 0 {
-		t.Fatal("expected no dirty state object")
+	s.state.RevertToSnapshot(snapshot)
+	if len(s.state.stateObjectsDirty) != 0 {
+		c.Fatal("expected no dirty state object")
 	}
 }
diff --git a/core/state/sync_test.go b/core/state/sync_test.go
index 108ebb320..06c572ea6 100644
--- a/core/state/sync_test.go
+++ b/core/state/sync_test.go
@@ -36,9 +36,10 @@ type testAccount struct {
 }
 
 // makeTestState create a sample test state to test node-wise reconstruction.
-func makeTestState() (ethdb.Database, common.Hash, []*testAccount) {
+func makeTestState() (Database, *ethdb.MemDatabase, common.Hash, []*testAccount) {
 	// Create an empty state
-	db, _ := ethdb.NewMemDatabase()
+	mem, _ := ethdb.NewMemDatabase()
+	db := NewDatabase(mem)
 	state, _ := New(common.Hash{}, db)
 
 	// Fill it with some arbitrary data
@@ -60,17 +61,17 @@ func makeTestState() (ethdb.Database, common.Hash, []*testAccount) {
 		state.updateStateObject(obj)
 		accounts = append(accounts, acc)
 	}
-	root, _ := state.Commit(false)
+	root, _ := state.CommitTo(mem, false)
 
 	// Return the generated state
-	return db, root, accounts
+	return db, mem, root, accounts
 }
 
 // checkStateAccounts cross references a reconstructed state with an expected
 // account array.
 func checkStateAccounts(t *testing.T, db ethdb.Database, root common.Hash, accounts []*testAccount) {
 	// Check root availability and state contents
-	state, err := New(root, db)
+	state, err := New(root, NewDatabase(db))
 	if err != nil {
 		t.Fatalf("failed to create state trie at %x: %v", root, err)
 	}
@@ -90,13 +91,28 @@ func checkStateAccounts(t *testing.T, db ethdb.Database, root common.Hash, accou
 	}
 }
 
-// checkStateConsistency checks that all nodes in a state trie are indeed present.
+// checkTrieConsistency checks that all nodes in a (sub-)trie are indeed present.
+func checkTrieConsistency(db ethdb.Database, root common.Hash) error {
+	if v, _ := db.Get(root[:]); v == nil {
+		return nil // Consider a non existent state consistent.
+	}
+	trie, err := trie.New(root, db)
+	if err != nil {
+		return err
+	}
+	it := trie.NodeIterator(nil)
+	for it.Next(true) {
+	}
+	return it.Error()
+}
+
+// checkStateConsistency checks that all data of a state root is present.
 func checkStateConsistency(db ethdb.Database, root common.Hash) error {
 	// Create and iterate a state trie rooted in a sub-node
 	if _, err := db.Get(root.Bytes()); err != nil {
-		return nil // Consider a non existent state consistent
+		return nil // Consider a non existent state consistent.
 	}
-	state, err := New(root, db)
+	state, err := New(root, NewDatabase(db))
 	if err != nil {
 		return err
 	}
@@ -122,7 +138,7 @@ func TestIterativeStateSyncBatched(t *testing.T)    { testIterativeStateSync(t,
 
 func testIterativeStateSync(t *testing.T, batch int) {
 	// Create a random state to copy
-	srcDb, srcRoot, srcAccounts := makeTestState()
+	_, srcMem, srcRoot, srcAccounts := makeTestState()
 
 	// Create a destination state and sync with the scheduler
 	dstDb, _ := ethdb.NewMemDatabase()
@@ -132,7 +148,7 @@ func testIterativeStateSync(t *testing.T, batch int) {
 	for len(queue) > 0 {
 		results := make([]trie.SyncResult, len(queue))
 		for i, hash := range queue {
-			data, err := srcDb.Get(hash.Bytes())
+			data, err := srcMem.Get(hash.Bytes())
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", hash, err)
 			}
@@ -154,7 +170,7 @@ func testIterativeStateSync(t *testing.T, batch int) {
 // partial results are returned, and the others sent only later.
 func TestIterativeDelayedStateSync(t *testing.T) {
 	// Create a random state to copy
-	srcDb, srcRoot, srcAccounts := makeTestState()
+	_, srcMem, srcRoot, srcAccounts := makeTestState()
 
 	// Create a destination state and sync with the scheduler
 	dstDb, _ := ethdb.NewMemDatabase()
@@ -165,7 +181,7 @@ func TestIterativeDelayedStateSync(t *testing.T) {
 		// Sync only half of the scheduled nodes
 		results := make([]trie.SyncResult, len(queue)/2+1)
 		for i, hash := range queue[:len(results)] {
-			data, err := srcDb.Get(hash.Bytes())
+			data, err := srcMem.Get(hash.Bytes())
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", hash, err)
 			}
@@ -191,7 +207,7 @@ func TestIterativeRandomStateSyncBatched(t *testing.T)    { testIterativeRandomS
 
 func testIterativeRandomStateSync(t *testing.T, batch int) {
 	// Create a random state to copy
-	srcDb, srcRoot, srcAccounts := makeTestState()
+	_, srcMem, srcRoot, srcAccounts := makeTestState()
 
 	// Create a destination state and sync with the scheduler
 	dstDb, _ := ethdb.NewMemDatabase()
@@ -205,7 +221,7 @@ func testIterativeRandomStateSync(t *testing.T, batch int) {
 		// Fetch all the queued nodes in a random order
 		results := make([]trie.SyncResult, 0, len(queue))
 		for hash := range queue {
-			data, err := srcDb.Get(hash.Bytes())
+			data, err := srcMem.Get(hash.Bytes())
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", hash, err)
 			}
@@ -231,7 +247,7 @@ func testIterativeRandomStateSync(t *testing.T, batch int) {
 // partial results are returned (Even those randomly), others sent only later.
 func TestIterativeRandomDelayedStateSync(t *testing.T) {
 	// Create a random state to copy
-	srcDb, srcRoot, srcAccounts := makeTestState()
+	_, srcMem, srcRoot, srcAccounts := makeTestState()
 
 	// Create a destination state and sync with the scheduler
 	dstDb, _ := ethdb.NewMemDatabase()
@@ -247,7 +263,7 @@ func TestIterativeRandomDelayedStateSync(t *testing.T) {
 		for hash := range queue {
 			delete(queue, hash)
 
-			data, err := srcDb.Get(hash.Bytes())
+			data, err := srcMem.Get(hash.Bytes())
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", hash, err)
 			}
@@ -276,7 +292,9 @@ func TestIterativeRandomDelayedStateSync(t *testing.T) {
 // the database.
 func TestIncompleteStateSync(t *testing.T) {
 	// Create a random state to copy
-	srcDb, srcRoot, srcAccounts := makeTestState()
+	_, srcMem, srcRoot, srcAccounts := makeTestState()
+
+	checkTrieConsistency(srcMem, srcRoot)
 
 	// Create a destination state and sync with the scheduler
 	dstDb, _ := ethdb.NewMemDatabase()
@@ -288,7 +306,7 @@ func TestIncompleteStateSync(t *testing.T) {
 		// Fetch a batch of state nodes
 		results := make([]trie.SyncResult, len(queue))
 		for i, hash := range queue {
-			data, err := srcDb.Get(hash.Bytes())
+			data, err := srcMem.Get(hash.Bytes())
 			if err != nil {
 				t.Fatalf("failed to retrieve node data for %x: %v", hash, err)
 			}
@@ -304,21 +322,18 @@ func TestIncompleteStateSync(t *testing.T) {
 		for _, result := range results {
 			added = append(added, result.Hash)
 		}
-		// Check that all known sub-tries in the synced state is complete
-		for _, root := range added {
-			// Skim through the accounts and make sure the root hash is not a code node
-			codeHash := false
+		// Check that all known sub-tries added so far are complete or missing entirely.
+	checkSubtries:
+		for _, hash := range added {
 			for _, acc := range srcAccounts {
-				if root == crypto.Keccak256Hash(acc.code) {
-					codeHash = true
-					break
+				if hash == crypto.Keccak256Hash(acc.code) {
+					continue checkSubtries // skip trie check of code nodes.
 				}
 			}
-			// If the root is a real trie node, check consistency
-			if !codeHash {
-				if err := checkStateConsistency(dstDb, root); err != nil {
-					t.Fatalf("state inconsistent: %v", err)
-				}
+			// Can't use checkStateConsistency here because subtrie keys may have odd
+			// length and crash in LeafKey.
+			if err := checkTrieConsistency(dstDb, hash); err != nil {
+				t.Fatalf("state inconsistent: %v", err)
 			}
 		}
 		// Fetch the next batch to retrieve