diff --git a/merkle/iavl_node.go b/merkle/iavl_node.go
index a94b557d..a2865205 100644
--- a/merkle/iavl_node.go
+++ b/merkle/iavl_node.go
@@ -10,43 +10,71 @@ import (
 // Node
 
 type IAVLNode struct {
-	key    []byte
-	value  []byte
-	size   uint64
-	height uint8
-	hash   []byte
-	left   *IAVLNode
-	right  *IAVLNode
+	key       []byte
+	value     []byte
+	size      uint64
+	height    uint8
+	hash      []byte
+	leftHash  []byte
+	rightHash []byte
+	persisted bool
 
-	// volatile
-	flags byte
+	// May or may not be persisted nodes, but they'll get cleared
+	// when this this node is saved.
+	leftCached  *IAVLNode
+	rightCached *IAVLNode
 }
 
-const (
-	IAVLNODE_FLAG_PERSISTED   = byte(0x01)
-	IAVLNODE_FLAG_PLACEHOLDER = byte(0x02)
-)
-
 func NewIAVLNode(key []byte, value []byte) *IAVLNode {
 	return &IAVLNode{
-		key:   key,
-		value: value,
-		size:  1,
+		key:       key,
+		value:     value,
+		size:      1,
+		persisted: false,
 	}
 }
 
+func ReadIAVLNode(r io.Reader, n *int64, err *error) *IAVLNode {
+	node := &IAVLNode{}
+
+	// node header & key
+	node.height = ReadUInt8(r, &n, &err)
+	node.size = ReadUInt64(r, &n, &err)
+	node.key = ReadByteSlice(r, &n, &err)
+	if err != nil {
+		panic(err)
+	}
+
+	// node value or children.
+	if node.height == 0 {
+		// value
+		node.value = ReadByteSlice(r, &n, &err)
+	} else {
+		// left
+		node.leftHash = ReadByteSlice(r, &n, &err)
+		// right
+		node.rightHash = ReadByteSlice(r, &n, &err)
+	}
+	if err != nil {
+		panic(err)
+	}
+	return node
+}
+
 func (self *IAVLNode) Copy() *IAVLNode {
 	if self.height == 0 {
 		panic("Why are you copying a value node?")
 	}
 	return &IAVLNode{
-		key:    self.key,
-		size:   self.size,
-		height: self.height,
-		left:   self.left,
-		right:  self.right,
-		hash:   nil,
-		flags:  byte(0),
+		key:         self.key,
+		size:        self.size,
+		height:      self.height,
+		hash:        nil, // Going to be mutated anyways.
+		leftHash:    self.leftHash,
+		rightHash:   self.rightHash,
+		persisted:   self.persisted,
+		leftCached:  self.leftCached,
+		rightCached: self.rightCached,
 	}
 }
 
@@ -58,7 +86,7 @@ func (self *IAVLNode) Height() uint8 {
 	return self.height
 }
 
-func (self *IAVLNode) has(db Db, key []byte) (has bool) {
+func (self *IAVLNode) has(ndb *IAVLNodeDB, key []byte) (has bool) {
 	if bytes.Equal(self.key, key) {
 		return true
 	}
@@ -66,14 +94,14 @@ func (self *IAVLNode) has(db Db, key []byte) (has bool) {
 		return false
 	} else {
 		if bytes.Compare(key, self.key) == -1 {
-			return self.leftFilled(db).has(db, key)
+			return self.getLeft(ndb).has(ndb, key)
 		} else {
-			return self.rightFilled(db).has(db, key)
+			return self.getRight(ndb).has(ndb, key)
 		}
 	}
 }
 
-func (self *IAVLNode) get(db Db, key []byte) (value []byte) {
+func (self *IAVLNode) get(ndb *IAVLNodeDB, key []byte) (value []byte) {
 	if self.height == 0 {
 		if bytes.Equal(self.key, key) {
 			return self.value
@@ -82,9 +110,9 @@ func (self *IAVLNode) get(db Db, key []byte) (value []byte) {
 		}
 	} else {
 		if bytes.Compare(key, self.key) == -1 {
-			return self.leftFilled(db).get(db, key)
+			return self.getLeft(ndb).get(ndb, key)
 		} else {
-			return self.rightFilled(db).get(db, key)
+			return self.getRight(ndb).get(ndb, key)
 		}
 	}
 }
@@ -104,105 +132,108 @@ func (self *IAVLNode) HashWithCount() ([]byte, uint64) {
 	return self.hash, hashCount + 1
 }
 
-func (self *IAVLNode) Save(db Db) {
+func (self *IAVLNode) Save(ndb *IAVLNodeDB) []byte {
 	if self.hash == nil {
-		panic("savee.hash can't be nil")
+		hash, _ := self.HashWithCount()
+		self.hash = hash
 	}
-	if self.flags&IAVLNODE_FLAG_PERSISTED > 0 ||
-		self.flags&IAVLNODE_FLAG_PLACEHOLDER > 0 {
-		return
+	if self.persisted {
+		return self.hash
 	}
 
 	// children
-	if self.height > 0 {
-		self.left.Save(db)
-		self.right.Save(db)
+	if self.leftCached != nil {
+		self.leftHash = self.leftCached.Save(ndb)
+		self.leftCached = nil
+	}
+	if self.rightCached != nil {
+		self.rightHash = self.rightCached.Save(ndb)
+		self.rightCached = nil
 	}
 
 	// save self
-	buf := bytes.NewBuffer(nil)
-	_, err := self.WriteTo(buf)
-	if err != nil {
-		panic(err)
-	}
-	db.Set([]byte(self.hash), buf.Bytes())
-
-	self.flags |= IAVLNODE_FLAG_PERSISTED
+	ndb.Save(self)
+	return self.hash
 }
 
-func (self *IAVLNode) set(db Db, key []byte, value []byte) (_ *IAVLNode, updated bool) {
+func (self *IAVLNode) set(ndb *IAVLNodeDB, key []byte, value []byte) (_ *IAVLNode, updated bool) {
 	if self.height == 0 {
 		if bytes.Compare(key, self.key) == -1 {
 			return &IAVLNode{
-				key:    self.key,
-				height: 1,
-				size:   2,
-				left:   NewIAVLNode(key, value),
-				right:  self,
+				key:         self.key,
+				height:      1,
+				size:        2,
+				leftCached:  NewIAVLNode(key, value),
+				rightCached: self,
 			}, false
 		} else if bytes.Equal(self.key, key) {
 			return NewIAVLNode(key, value), true
 		} else {
 			return &IAVLNode{
-				key:    key,
-				height: 1,
-				size:   2,
-				left:   self,
-				right:  NewIAVLNode(key, value),
+				key:         key,
+				height:      1,
+				size:        2,
+				leftCached:  self,
+				rightCached: NewIAVLNode(key, value),
 			}, false
 		}
 	} else {
 		self = self.Copy()
 		if bytes.Compare(key, self.key) == -1 {
-			self.left, updated = self.leftFilled(db).set(db, key, value)
+			self.leftCached, updated = self.getLeft(ndb).set(ndb, key, value)
+			self.leftHash = nil
 		} else {
-			self.right, updated = self.rightFilled(db).set(db, key, value)
+			self.rightCached, updated = self.getRight(ndb).set(ndb, key, value)
+			self.rightHash = nil
 		}
 		if updated {
 			return self, updated
 		} else {
-			self.calcHeightAndSize(db)
-			return self.balance(db), updated
+			self.calcHeightAndSize(ndb)
+			return self.balance(ndb), updated
 		}
 	}
 }
 
 // newKey: new leftmost leaf key for tree after successfully removing 'key' if changed.
-func (self *IAVLNode) remove(db Db, key []byte) (newSelf *IAVLNode, newKey []byte, value []byte, err error) {
+// only one of newSelfHash or newSelf is returned.
+func (self *IAVLNode) remove(ndb *IAVLNodeDB, key []byte) (newSelfHash []byte, newSelf *IAVLNode, newKey []byte, value []byte, err error) {
 	if self.height == 0 {
 		if bytes.Equal(self.key, key) {
-			return nil, nil, self.value, nil
+			return nil, nil, nil, self.value, nil
 		} else {
-			return self, nil, nil, NotFound(key)
+			return nil, self, nil, nil, NotFound(key)
 		}
 	} else {
 		if bytes.Compare(key, self.key) == -1 {
+			var newLeftHash []byte
 			var newLeft *IAVLNode
-			newLeft, newKey, value, err = self.leftFilled(db).remove(db, key)
+			newLeftHash, newLeft, newKey, value, err = self.getLeft(ndb).remove(ndb, key)
 			if err != nil {
-				return self, nil, value, err
-			} else if newLeft == nil { // left node held value, was removed
-				return self.right, self.key, value, nil
+				return nil, self, nil, value, err
+			} else if newLeftHash == nil && newLeft == nil { // left node held value, was removed
+				return self.rightHash, self.rightCached, self.key, value, nil
 			}
 			self = self.Copy()
-			self.left = newLeft
+			self.leftHash, self.leftCached = newLeftHash, newLeft
 		} else {
+			var newRightHash []byte
 			var newRight *IAVLNode
-			newRight, newKey, value, err = self.rightFilled(db).remove(db, key)
+			newRightHash, newRight, newKey, value, err = self.getRight(ndb).remove(ndb, key)
 			if err != nil {
-				return self, nil, value, err
-			} else if newRight == nil { // right node held value, was removed
-				return self.left, nil, value, nil
+				return nil, self, nil, value, err
+			} else if newRightHash == nil && newRight == nil { // right node held value, was removed
+				return self.leftHash, self.leftCached, nil, value, nil
 			}
 			self = self.Copy()
-			self.right = newRight
+			self.rightHash, self.rightCached = newRightHash, newRight
 			if newKey != nil {
 				self.key = newKey
 				newKey = nil
 			}
 		}
-		self.calcHeightAndSize(db)
-		return self.balance(db), newKey, value, err
+		self.calcHeightAndSize(ndb)
+		return nil, self.balance(ndb), newKey, value, err
 	}
 }
 
@@ -226,170 +257,133 @@ func (self *IAVLNode) saveToCountHashes(w io.Writer) (n int64, hashCount uint64,
 		WriteByteSlice(w, self.value, &n, &err)
 	} else {
 		// left
-		leftHash, leftCount := self.left.HashWithCount()
-		hashCount += leftCount
-		WriteByteSlice(w, leftHash, &n, &err)
+		if self.leftCached != nil {
+			leftHash, leftCount := self.left.HashWithCount()
+			self.leftHash = leftHash
+			hashCount += leftCount
+		}
+		WriteByteSlice(w, self.leftHash, &n, &err)
 		// right
-		rightHash, rightCount := self.right.HashWithCount()
-		hashCount += rightCount
-		WriteByteSlice(w, rightHash, &n, &err)
+		if self.rightCached != nil {
+			rightHash, rightCount := self.right.HashWithCount()
+			self.rightHash = rightHash
+			hashCount += rightCount
+		}
+		WriteByteSlice(w, self.rightHash, &n, &err)
 	}
 	return
 }
 
-// Given a placeholder node which has only the hash set,
-// load the rest of the data from db.
-// Not threadsafe.
-func (self *IAVLNode) fill(db Db) {
-	if self.hash == nil {
-		panic("placeholder.hash can't be nil")
-	}
-	buf := db.Get(self.hash)
-	r := bytes.NewReader(buf)
-	var n int64
-	var err error
-
-	// node header & key
-	self.height = ReadUInt8(r, &n, &err)
-	self.size = ReadUInt64(r, &n, &err)
-	self.key = ReadByteSlice(r, &n, &err)
-	if err != nil {
-		panic(err)
-	}
-
-	// node value or children.
-	if self.height == 0 {
-		// value
-		self.value = ReadByteSlice(r, &n, &err)
+func (self *IAVLNode) getLeft(ndb *IAVLNodeDB) *IAVLNode {
+	if self.leftCached != nil {
+		return self.leftCached
 	} else {
-		// left
-		leftHash := ReadByteSlice(r, &n, &err)
-		self.left = &IAVLNode{
-			hash:  leftHash,
-			flags: IAVLNODE_FLAG_PERSISTED | IAVLNODE_FLAG_PLACEHOLDER,
-		}
-		// right
-		rightHash := ReadByteSlice(r, &n, &err)
-		self.right = &IAVLNode{
-			hash:  rightHash,
-			flags: IAVLNODE_FLAG_PERSISTED | IAVLNODE_FLAG_PLACEHOLDER,
-		}
-		if r.Len() != 0 {
-			panic("buf not all consumed")
-		}
+		return ndb.Get(leftHash)
 	}
-	if err != nil {
-		panic(err)
-	}
-	self.flags &= ^IAVLNODE_FLAG_PLACEHOLDER
 }
 
-func (self *IAVLNode) leftFilled(db Db) *IAVLNode {
-	if self.left.flags&IAVLNODE_FLAG_PLACEHOLDER > 0 {
-		self.left.fill(db)
+func (self *IAVLNode) getRight(ndb *IAVLNodeDB) *IAVLNode {
+	if self.rightCached != nil {
+		return self.rightCached
+	} else {
+		return ndb.Get(rightHash)
 	}
-	return self.left
 }
 
-func (self *IAVLNode) rightFilled(db Db) *IAVLNode {
-	if self.right.flags&IAVLNODE_FLAG_PLACEHOLDER > 0 {
-		self.right.fill(db)
-	}
-	return self.right
-}
-
-func (self *IAVLNode) rotateRight(db Db) *IAVLNode {
+func (self *IAVLNode) rotateRight(ndb *IAVLNodeDB) *IAVLNode {
 	self = self.Copy()
-	sl := self.leftFilled(db).Copy()
-	slr := sl.right
+	sl := self.getLeft(ndb).Copy()
 
-	sl.right = self
-	self.left = slr
+	slrHash, slrCached := sl.rightHash, sl.rightCached
+	sl.rightHash, sl.rightCached = nil, self
+	self.leftHash, self.leftCached = slrHash, slrCached
 
-	self.calcHeightAndSize(db)
-	sl.calcHeightAndSize(db)
+	self.calcHeightAndSize(ndb)
+	sl.calcHeightAndSize(ndb)
 
 	return sl
 }
 
-func (self *IAVLNode) rotateLeft(db Db) *IAVLNode {
+func (self *IAVLNode) rotateLeft(ndb *IAVLNodeDB) *IAVLNode {
 	self = self.Copy()
-	sr := self.rightFilled(db).Copy()
-	srl := sr.left
+	sr := self.getRight(ndb).Copy()
 
-	sr.left = self
-	self.right = srl
+	srlHash, srlCached := sr.leftHash, sr.leftCached
+	sr.leftHash, sr.leftCached = nil, self
+	self.rightHash, self.rightCached = srlHash, srlCached
 
-	self.calcHeightAndSize(db)
-	sr.calcHeightAndSize(db)
+	self.calcHeightAndSize(ndb)
+	sr.calcHeightAndSize(ndb)
 
 	return sr
 }
 
-func (self *IAVLNode) calcHeightAndSize(db Db) {
-	self.height = maxUint8(self.leftFilled(db).Height(), self.rightFilled(db).Height()) + 1
-	self.size = self.leftFilled(db).Size() + self.rightFilled(db).Size()
+func (self *IAVLNode) calcHeightAndSize(ndb *IAVLNodeDB) {
+	self.height = maxUint8(self.getLeft(ndb).Height(), self.getRight(ndb).Height()) + 1
+	self.size = self.getLeft(ndb).Size() + self.getRight(ndb).Size()
 }
 
-func (self *IAVLNode) calcBalance(db Db) int {
-	return int(self.leftFilled(db).Height()) - int(self.rightFilled(db).Height())
+func (self *IAVLNode) calcBalance(ndb *IAVLNodeDB) int {
+	return int(self.getLeft(ndb).Height()) - int(self.getRight(ndb).Height())
 }
 
-func (self *IAVLNode) balance(db Db) (newSelf *IAVLNode) {
-	balance := self.calcBalance(db)
+func (self *IAVLNode) balance(ndb *IAVLNodeDB) (newSelf *IAVLNode) {
+	balance := self.calcBalance(ndb)
 	if balance > 1 {
-		if self.leftFilled(db).calcBalance(db) >= 0 {
+		if self.getLeft(ndb).calcBalance(ndb) >= 0 {
 			// Left Left Case
-			return self.rotateRight(db)
+			return self.rotateRight(ndb)
 		} else {
 			// Left Right Case
 			self = self.Copy()
-			self.left = self.leftFilled(db).rotateLeft(db)
+			self.leftHash, self.leftCached = nil, self.getLeft(ndb).rotateLeft(ndb)
 			//self.calcHeightAndSize()
-			return self.rotateRight(db)
+			return self.rotateRight(ndb)
 		}
 	}
 	if balance < -1 {
-		if self.rightFilled(db).calcBalance(db) <= 0 {
+		if self.getRight(ndb).calcBalance(ndb) <= 0 {
 			// Right Right Case
-			return self.rotateLeft(db)
+			return self.rotateLeft(ndb)
 		} else {
 			// Right Left Case
 			self = self.Copy()
-			self.right = self.rightFilled(db).rotateRight(db)
+			self.rightHash, self.rightCached = nil, self.getRight(ndb).rotateRight(ndb)
 			//self.calcHeightAndSize()
-			return self.rotateLeft(db)
+			return self.rotateLeft(ndb)
 		}
 	}
 	// Nothing changed
 	return self
 }
 
-func (self *IAVLNode) lmd(db Db) *IAVLNode {
+// Only used in testing...
+func (self *IAVLNode) lmd(ndb *IAVLNodeDB) *IAVLNode {
 	if self.height == 0 {
 		return self
 	}
-	return self.leftFilled(db).lmd(db)
+	return self.getLeft(ndb).lmd(ndb)
 }
 
-func (self *IAVLNode) rmd(db Db) *IAVLNode {
+// Only used in testing...
+func (self *IAVLNode) rmd(ndb *IAVLNodeDB) *IAVLNode {
 	if self.height == 0 {
 		return self
 	}
-	return self.rightFilled(db).rmd(db)
+	return self.getRight(ndb).rmd(ndb)
 }
 
-func (self *IAVLNode) traverse(db Db, cb func(*IAVLNode) bool) bool {
+func (self *IAVLNode) traverse(ndb *IAVLNodeDB, cb func(*IAVLNode) bool) bool {
 	stop := cb(self)
 	if stop {
 		return stop
 	}
 	if self.height > 0 {
-		stop = self.leftFilled(db).traverse(db, cb)
+		stop = self.getLeft(ndb).traverse(ndb, cb)
 		if stop {
 			return stop
 		}
-		stop = self.rightFilled(db).traverse(db, cb)
+		stop = self.getRight(ndb).traverse(ndb, cb)
 		if stop {
 			return stop
 		}
diff --git a/merkle/iavl_tree.go b/merkle/iavl_tree.go
index d35b64c8..58323e9b 100644
--- a/merkle/iavl_tree.go
+++ b/merkle/iavl_tree.go
@@ -9,38 +9,24 @@ This tree is not concurrency safe.
 You must wrap your calls with your own mutex.
 */
 type IAVLTree struct {
-	db   Db
+	ndb  IAVLNodeDB
 	root *IAVLNode
 }
 
-func NewIAVLTree(db Db) *IAVLTree {
+func NewIAVLTree(db DB) *IAVLTree {
 	return &IAVLTree{
-		db:   db,
+		ndb:  NewIAVLNodeDB(db),
 		root: nil,
 	}
 }
 
-// TODO rename to Load.
-func NewIAVLTreeFromHash(db Db, hash []byte) *IAVLTree {
-	root := &IAVLNode{
-		hash:  hash,
-		flags: IAVLNODE_FLAG_PERSISTED | IAVLNODE_FLAG_PLACEHOLDER,
-	}
-	root.fill(db)
-	return &IAVLTree{db: db, root: root}
-}
-
-func NewIAVLTreeFromKey(db Db, key string) *IAVLTree {
-	hash := db.Get([]byte(key))
-	if hash == nil {
+func LoadIAVLTreeFromHash(db DB, hash []byte) *IAVLTree {
+	ndb := NewIAVLNodeDB(db)
+	root := ndb.Get(hash)
+	if root == nil {
 		return nil
 	}
-	root := &IAVLNode{
-		hash:  hash,
-		flags: IAVLNODE_FLAG_PERSISTED | IAVLNODE_FLAG_PLACEHOLDER,
-	}
-	root.fill(db)
-	return &IAVLTree{db: db, root: root}
+	return &IAVLTree{ndb: ndb, root: root}
 }
 
 func (t *IAVLTree) Size() uint64 {
@@ -61,7 +47,7 @@ func (t *IAVLTree) Has(key []byte) bool {
 	if t.root == nil {
 		return false
 	}
-	return t.root.has(t.db, key)
+	return t.root.has(t.ndb, key)
 }
 
 func (t *IAVLTree) Set(key []byte, value []byte) (updated bool) {
@@ -69,7 +55,7 @@ func (t *IAVLTree) Set(key []byte, value []byte) (updated bool) {
 		t.root = NewIAVLNode(key, value)
 		return false
 	}
-	t.root, updated = t.root.set(t.db, key, value)
+	t.root, updated = t.root.set(t.ndb, key, value)
 	return updated
 }
 
@@ -93,7 +79,7 @@ func (t *IAVLTree) Save() {
 		return
 	}
 	t.root.HashWithCount()
-	t.root.Save(t.db)
+	t.root.Save(t.ndb)
 }
 
 func (t *IAVLTree) SaveKey(key string) {
@@ -101,29 +87,70 @@ func (t *IAVLTree) SaveKey(key string) {
 		return
 	}
 	hash, _ := t.root.HashWithCount()
-	t.root.Save(t.db)
-	t.db.Set([]byte(key), hash)
+	t.root.Save(t.ndb)
+	t.ndb.Set([]byte(key), hash)
 }
 
 func (t *IAVLTree) Get(key []byte) (value []byte) {
 	if t.root == nil {
 		return nil
 	}
-	return t.root.get(t.db, key)
+	return t.root.get(t.ndb, key)
 }
 
 func (t *IAVLTree) Remove(key []byte) (value []byte, err error) {
 	if t.root == nil {
 		return nil, NotFound(key)
 	}
-	newRoot, _, value, err := t.root.remove(t.db, key)
+	newRootHash, newRoot, _, value, err := t.root.remove(t.ndb, key)
 	if err != nil {
 		return nil, err
 	}
-	t.root = newRoot
+	if newRoot == nil && newRootHash != nil {
+		t.root = t.ndb.Get(newRootHash)
+	} else {
+		t.root = newRoot
+	}
 	return value, nil
 }
 
 func (t *IAVLTree) Copy() Tree {
-	return &IAVLTree{db: t.db, root: t.root}
+	return &IAVLTree{ndb: t.ndb, root: t.root}
+}
+
+//-----------------------------------------------------------------------------
+
+type IAVLNodeDB struct {
+	db    DB
+	cache map[string]*IAVLNode
+	// XXX expire entries
+}
+
+func (ndb *IAVLNodeDB) Get(hash []byte) *IAVLNode {
+	buf := ndb.db.Get(hash)
+	r := bytes.NewReader(buf)
+	var n int64
+	var err error
+	node := ReadIAVLNode(r, &n, &err)
+	if err != nil {
+		panic(err)
+	}
+	node.persisted = true
+	ndb.cache[string(hash)] = node
+	return node
+}
+
+func (ndb *IAVLNodeDB) Save(node *IAVLNode) {
+	hash := node.hash
+	if hash != nil {
+		panic("Expected to find node.hash, but none found.")
+	}
+	buf := bytes.NewBuffer(nil)
+	_, err := self.WriteTo(buf)
+	if err != nil {
+		panic(err)
+	}
+	node.persisted = true
+	ndb.cache[string(hash)] = node
+	ndb.db.Set(hash, buf.Bytes())
 }
diff --git a/merkle/types.go b/merkle/types.go
index 35d3ef42..396eb21b 100644
--- a/merkle/types.go
+++ b/merkle/types.go
@@ -4,7 +4,7 @@ import (
 	"fmt"
 )
 
-type Db interface {
+type DB interface {
 	Get([]byte) []byte
 	Set([]byte, []byte)
 }