diff --git a/nodemgr/nm.go b/nodemgr/nm.go
index 318f0d0..3131aae 100644
--- a/nodemgr/nm.go
+++ b/nodemgr/nm.go
@@ -5,6 +5,7 @@ import (
 	"encoding/gob"
 	"fmt"
 	"sort"
+	"sync"
 
 	"github.com/lbryio/claimtrie/change"
 	"github.com/lbryio/claimtrie/claim"
@@ -17,8 +18,11 @@ import (
 // NodeMgr ...
 type NodeMgr struct {
 	height claim.Height
+	db     *leveldb.DB
 
-	db          *leveldb.DB
+	// cachemu synchronizes the access to the map itself, but not the
+	// values of the node.
+	cachemu     sync.RWMutex
 	cache       map[string]*claim.Node
 	nextUpdates todos
 }
@@ -35,12 +39,16 @@ func New(db *leveldb.DB) *NodeMgr {
 
 // Load loads the nodes from the database up to height ht.
 func (nm *NodeMgr) Load(ht claim.Height) {
+
 	nm.height = ht
 	iter := nm.db.NewIterator(nil, nil)
+	nm.cachemu.Lock()
 	for iter.Next() {
 		name := string(iter.Key())
 		nm.cache[name] = nm.load(name, ht)
 	}
+	nm.cachemu.Unlock()
+
 	data, err := nm.db.Get([]byte("nextUpdates"), nil)
 	if err == leveldb.ErrNotFound {
 		return
@@ -71,6 +79,8 @@ func (nm *NodeMgr) Get(key []byte) trie.Value {
 
 // Reset resets all nodes to specified height.
 func (nm *NodeMgr) Reset(ht claim.Height) {
+	nm.cachemu.Lock()
+	defer nm.cachemu.Unlock()
 	nm.height = ht
 	for name, n := range nm.cache {
 		if n.Height() >= ht {
@@ -81,21 +91,25 @@ func (nm *NodeMgr) Reset(ht claim.Height) {
 
 // Size returns the number of nodes loaded into the cache.
 func (nm *NodeMgr) Size() int {
+	nm.cachemu.RLock()
+	defer nm.cachemu.RUnlock()
 	return len(nm.cache)
 }
 
 func (nm *NodeMgr) load(name string, ht claim.Height) *claim.Node {
 	c := change.NewChangeList(nm.db, name).Load().Truncate(ht).Changes()
-	return NewFromChanges(name, c, ht)
+	return replay(name, c).AdjustTo(ht)
 }
 
 // NodeAt returns the node adjusted to specified height.
 func (nm *NodeMgr) NodeAt(name string, ht claim.Height) *claim.Node {
+	nm.cachemu.Lock()
 	n, ok := nm.cache[name]
 	if !ok {
 		n = claim.NewNode(name)
 		nm.cache[name] = n
 	}
+	nm.cachemu.Unlock()
 
 	// Cached version is too new.
 	if n.Height() > nm.height || n.Height() > ht {
@@ -112,7 +126,9 @@ func (nm *NodeMgr) ModifyNode(name string, chg *change.Change) error {
 	if err := execute(n, chg); err != nil {
 		return errors.Wrapf(err, "claim.execute(n,chg)")
 	}
+	nm.cachemu.Lock()
 	nm.cache[name] = n
+	nm.cachemu.Unlock()
 	nm.nextUpdates.set(name, ht+1)
 	change.NewChangeList(nm.db, name).Load().Append(chg).Save()
 	return nil
@@ -129,11 +145,14 @@ func (nm *NodeMgr) CatchUp(ht claim.Height, notifier func(key []byte)) {
 	}
 }
 
-// VisitFunc ...
+// VisitFunc visit each node in read-only manner.
 type VisitFunc func(n *claim.Node) (stop bool)
 
-// Visit visits every node in the cache with VisiFunc.
+// Visit visits every node in the cache with VisitFunc.
+// If the VisitFunc returns true, the iteration ends immediately.
 func (nm *NodeMgr) Visit(v VisitFunc) {
+	nm.cachemu.RLock()
+	defer nm.cachemu.RUnlock()
 	for _, n := range nm.cache {
 		if v(n) {
 			return
@@ -141,7 +160,7 @@ func (nm *NodeMgr) Visit(v VisitFunc) {
 	}
 }
 
-// Show is a conevenient function for debugging and velopment purpose.
+// Show is a conevenient function for debugging purpose.
 // The proper way to handle user request would be a query function with filters specified.
 func (nm *NodeMgr) Show(name string, ht claim.Height, dump bool) error {
 	names := []string{}
@@ -166,11 +185,6 @@ func (nm *NodeMgr) Show(name string, ht claim.Height, dump bool) error {
 	return nil
 }
 
-// NewFromChanges ...
-func NewFromChanges(name string, chgs []*change.Change, ht claim.Height) *claim.Node {
-	return replay(name, chgs).AdjustTo(ht)
-}
-
 func replay(name string, chgs []*change.Change) *claim.Node {
 	n := claim.NewNode(name)
 	for _, chg := range chgs {