trie: improve the node iterator seek operation

trie/iterator.go

@@ -243,7 +243,7 @@ func (it *nodeIterator) seek(prefix []byte) error {
 	key = key[:len(key)-1]
 	// Move forward until we're just before the closest match to key.
 	for {
-		state, parentIndex, path, err := it.peek(bytes.HasPrefix(key, it.path))
+		state, parentIndex, path, err := it.peekSeek(key)
 		if err == errIteratorEnd {
 			return errIteratorEnd
 		} else if err != nil {
@@ -292,6 +292,44 @@ func (it *nodeIterator) peek(descend bool) (*nodeIteratorState, *int, []byte, er
 	return nil, nil, nil, errIteratorEnd
 }
 
+// peekSeek is like peek, but it also tries to skip resolving hashes by skipping
+// over the siblings that do not lead towards the desired seek position.
+func (it *nodeIterator) peekSeek(seekKey []byte) (*nodeIteratorState, *int, []byte, error) {
+	if len(it.stack) == 0 {
+		// Initialize the iterator if we've just started.
+		root := it.trie.Hash()
+		state := &nodeIteratorState{node: it.trie.root, index: -1}
+		if root != emptyRoot {
+			state.hash = root
+		}
+		err := state.resolve(it.trie, nil)
+		return state, nil, nil, err
+	}
+	if !bytes.HasPrefix(seekKey, it.path) {
+		// If we're skipping children, pop the current node first
+		it.pop()
+	}
+
+	// Continue iteration to the next child
+	for len(it.stack) > 0 {
+		parent := it.stack[len(it.stack)-1]
+		ancestor := parent.hash
+		if (ancestor == common.Hash{}) {
+			ancestor = parent.parent
+		}
+		state, path, ok := it.nextChildAt(parent, ancestor, seekKey)
+		if ok {
+			if err := state.resolve(it.trie, path); err != nil {
+				return parent, &parent.index, path, err
+			}
+			return state, &parent.index, path, nil
+		}
+		// No more child nodes, move back up.
+		it.pop()
+	}
+	return nil, nil, nil, errIteratorEnd
+}
+
 func (st *nodeIteratorState) resolve(tr *Trie, path []byte) error {
 	if hash, ok := st.node.(hashNode); ok {
 		resolved, err := tr.resolveHash(hash, path)
@@ -304,25 +342,38 @@ func (st *nodeIteratorState) resolve(tr *Trie, path []byte) error {
 	return nil
 }
 
+func findChild(n *fullNode, index int, path []byte, ancestor common.Hash) (node, *nodeIteratorState, []byte, int) {
+	var (
+		child     node
+		state     *nodeIteratorState
+		childPath []byte
+	)
+	for ; index < len(n.Children); index++ {
+		if n.Children[index] != nil {
+			child = n.Children[index]
+			hash, _ := child.cache()
+			state = &nodeIteratorState{
+				hash:    common.BytesToHash(hash),
+				node:    child,
+				parent:  ancestor,
+				index:   -1,
+				pathlen: len(path),
+			}
+			childPath = append(childPath, path...)
+			childPath = append(childPath, byte(index))
+			return child, state, childPath, index
+		}
+	}
+	return nil, nil, nil, 0
+}
+
 func (it *nodeIterator) nextChild(parent *nodeIteratorState, ancestor common.Hash) (*nodeIteratorState, []byte, bool) {
 	switch node := parent.node.(type) {
 	case *fullNode:
-		// Full node, move to the first non-nil child.
-		for i := parent.index + 1; i < len(node.Children); i++ {
-			child := node.Children[i]
-			if child != nil {
-				hash, _ := child.cache()
-				state := &nodeIteratorState{
-					hash:    common.BytesToHash(hash),
-					node:    child,
-					parent:  ancestor,
-					index:   -1,
-					pathlen: len(it.path),
-				}
-				path := append(it.path, byte(i))
-				parent.index = i - 1
-				return state, path, true
-			}
+		//Full node, move to the first non-nil child.
+		if child, state, path, index := findChild(node, parent.index+1, it.path, ancestor); child != nil {
+			parent.index = index - 1
+			return state, path, true
 		}
 	case *shortNode:
 		// Short node, return the pointer singleton child
@@ -342,6 +393,52 @@ func (it *nodeIterator) nextChild(parent *nodeIteratorState, ancestor common.Has
 	return parent, it.path, false
 }
 
+// nextChildAt is similar to nextChild, except that it targets a child as close to the
+// target key as possible, thus skipping siblings.
+func (it *nodeIterator) nextChildAt(parent *nodeIteratorState, ancestor common.Hash, key []byte) (*nodeIteratorState, []byte, bool) {
+	switch n := parent.node.(type) {
+	case *fullNode:
+		// Full node, move to the first non-nil child before the desired key position
+		child, state, path, index := findChild(n, parent.index+1, it.path, ancestor)
+		if child == nil {
+			// No more children in this fullnode
+			return parent, it.path, false
+		}
+		// If the child we found is already past the seek position, just return it.
+		if bytes.Compare(path, key) >= 0 {
+			parent.index = index - 1
+			return state, path, true
+		}
+		// The child is before the seek position. Try advancing
+		for {
+			nextChild, nextState, nextPath, nextIndex := findChild(n, index+1, it.path, ancestor)
+			// If we run out of children, or skipped past the target, return the
+			// previous one
+			if nextChild == nil || bytes.Compare(nextPath, key) >= 0 {
+				parent.index = index - 1
+				return state, path, true
+			}
+			// We found a better child closer to the target
+			state, path, index = nextState, nextPath, nextIndex
+		}
+	case *shortNode:
+		// Short node, return the pointer singleton child
+		if parent.index < 0 {
+			hash, _ := n.Val.cache()
+			state := &nodeIteratorState{
+				hash:    common.BytesToHash(hash),
+				node:    n.Val,
+				parent:  ancestor,
+				index:   -1,
+				pathlen: len(it.path),
+			}
+			path := append(it.path, n.Key...)
+			return state, path, true
+		}
+	}
+	return parent, it.path, false
+}
+
 func (it *nodeIterator) push(state *nodeIteratorState, parentIndex *int, path []byte) {
 	it.path = path
 	it.stack = append(it.stack, state)

trie/iterator_test.go

@@ -18,11 +18,14 @@ package trie
 
 import (
 	"bytes"
+	"encoding/binary"
 	"fmt"
 	"math/rand"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/ethdb/memorydb"
 )
 
@@ -440,3 +443,81 @@ func checkIteratorNoDups(t *testing.T, it NodeIterator, seen map[string]bool) in
 	}
 	return len(seen)
 }
+
+type loggingDb struct {
+	getCount uint64
+	backend  ethdb.KeyValueStore
+}
+
+func (l *loggingDb) Has(key []byte) (bool, error) {
+	return l.backend.Has(key)
+}
+
+func (l *loggingDb) Get(key []byte) ([]byte, error) {
+	l.getCount++
+	return l.backend.Get(key)
+}
+
+func (l *loggingDb) Put(key []byte, value []byte) error {
+	return l.backend.Put(key, value)
+}
+
+func (l *loggingDb) Delete(key []byte) error {
+	return l.backend.Delete(key)
+}
+
+func (l *loggingDb) NewBatch() ethdb.Batch {
+	return l.backend.NewBatch()
+}
+
+func (l *loggingDb) NewIterator(prefix []byte, start []byte) ethdb.Iterator {
+	fmt.Printf("NewIterator\n")
+	return l.backend.NewIterator(prefix, start)
+}
+func (l *loggingDb) Stat(property string) (string, error) {
+	return l.backend.Stat(property)
+}
+
+func (l *loggingDb) Compact(start []byte, limit []byte) error {
+	return l.backend.Compact(start, limit)
+}
+
+func (l *loggingDb) Close() error {
+	return l.backend.Close()
+}
+
+// makeLargeTestTrie create a sample test trie
+func makeLargeTestTrie() (*Database, *SecureTrie, *loggingDb) {
+	// Create an empty trie
+	logDb := &loggingDb{0, memorydb.New()}
+	triedb := NewDatabase(logDb)
+	trie, _ := NewSecure(common.Hash{}, triedb)
+
+	// Fill it with some arbitrary data
+	for i := 0; i < 10000; i++ {
+		key := make([]byte, 32)
+		val := make([]byte, 32)
+		binary.BigEndian.PutUint64(key, uint64(i))
+		binary.BigEndian.PutUint64(val, uint64(i))
+		key = crypto.Keccak256(key)
+		val = crypto.Keccak256(val)
+		trie.Update(key, val)
+	}
+	trie.Commit(nil)
+	// Return the generated trie
+	return triedb, trie, logDb
+}
+
+// Tests that the node iterator indeed walks over the entire database contents.
+func TestNodeIteratorLargeTrie(t *testing.T) {
+	// Create some arbitrary test trie to iterate
+	db, trie, logDb := makeLargeTestTrie()
+	db.Cap(0) // flush everything
+	// Do a seek operation
+	trie.NodeIterator(common.FromHex("0x77667766776677766778855885885885"))
+	// master: 24 get operations
+	// this pr: 5 get operations
+	if have, want := logDb.getCount, uint64(5); have != want {
+		t.Fatalf("Too many lookups during seek, have %d want %d", have, want)
+	}
+}