diff --git a/.vscode/settings.json b/.vscode/settings.json
index 0df7e95..bda7a87 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -30,6 +30,7 @@
         "assert.h": "c",
         "limits.h": "c",
         "cstdint": "c",
-        "unicstl_internal.h": "c"
+        "unicstl_internal.h": "c",
+        "map.h": "c"
     }
 }
\ No newline at end of file
diff --git a/include/map.h b/include/map.h
index 639a502..a8f0bc3 100644
--- a/include/map.h
+++ b/include/map.h
@@ -18,17 +18,16 @@ struct _map_node
 {
     char* key;
     void* value;
+    size_t key_sz;
+    size_t value_sz;
 };
+typedef struct _map_node * map_node_t;
 
 struct _map
 {
     // -------------------- private -------------------- 
     tree_t _tree;
-
-    // uint32_t _size;
     uint32_t _obj_size;
-    // uint32_t _capacity;
-    // uint32_t _ratio;
 
     // -------------------- public -------------------- 
     // kernel
@@ -46,9 +45,6 @@ struct _map
     // iter
     iterator_t(*iter)(struct _map* self, enum _tree_order);
 
-    // config 
-    compare_fun_t compare;  // !!! you have to implement this function
-
     // -------------------- debug -------------------- 
     void (*print_obj)(void* obj);
 };
diff --git a/src/map.c b/src/map.c
index c2b2cf5..2df2e1e 100644
--- a/src/map.c
+++ b/src/map.c
@@ -17,24 +17,22 @@ struct _map_node* map_node_new(struct _map *self, const char* key, void* value)
     {
         return NULL;
     }
-    uint32_t keylen = strlen(key) + 1;
-    node->key = (char*)malloc(sizeof(char) * keylen);
+
+    // Allocating memory for key and value only once can improve performance.
+    node->key_sz = strlen(key) + 1;
+    node->value_sz = self->_obj_size;
+    node->key = (char*)malloc(node->key_sz + node->value_sz);
     if (!node->key)
     {
         free(node);
         return NULL;
     }
+    node->value = node->key + node->key_sz;
 
-    node->value = malloc(self->_obj_size);
-    if (!node->value)
-    {
-        free(node->key);
-        free(node);
-        return NULL;
-    }
-    
-    memcpy(node->key, key, keylen);
-    memcpy(node->value, value, self->_obj_size);
+    // copy
+    memcpy(node->key, key, node->key_sz);
+    node->key[node->key_sz] = '\0';
+    memcpy(node->value, value, node->value_sz);
     return node;
 }
 
@@ -46,29 +44,11 @@ static void map_node_free(struct _map_node** node)
         {
             free((*node)->key);
         }
-        if ((*node)->value != NULL)
-        {
-            free((*node)->value);
-        }
         free(*node);
         *node = NULL;
     }
 }
 
-bool map_clear(struct _map* self)
-{
-    struct _map_node* node = NULL;
-    iterator_t iter = self->_tree->iter(self->_tree, TREE_DFS_IN);
-    while(iter->hasnext(&iter))
-    {
-        // tree & map malloc memory independently, so free them one by one.
-        node = (struct _map_node*)iter->next(&iter);
-        map_node_free(&node);
-    }
-
-    return self->_tree->clear(self->_tree);
-}
-
 bool map_empty(struct _map* self)
 {
     return self->_tree->empty(self->_tree);
@@ -79,6 +59,20 @@ uint32_t map_size(struct _map* self)
     return self->_tree->size(self->_tree);
 }
 
+bool map_clear(struct _map* self)
+{
+    struct _map_node* node = NULL;
+    iterator_t iter = self->_tree->iter(self->_tree, TREE_DFS_IN);
+    while(iter->hasnext(iter))
+    {
+        // tree & map malloc memory independently, so free them one by one.
+        node = (struct _map_node*)iter->next(iter);
+        map_node_free(&node);
+    }
+
+    return self->_tree->clear(self->_tree);
+}
+
 bool map_insert(struct _map* self, const char* key, void* value)
 {
     struct _map_node* node = NULL;
@@ -92,8 +86,8 @@ bool map_insert(struct _map* self, const char* key, void* value)
 
 bool map_delete(struct _map* self, const char* key, void* value)
 {
-    struct _map_node node = {.key = key, .value = value};
-    return self->_tree->delete(self->_tree, &node);
+    // struct _map_node node = {.key = key, .value = value};
+    // return self->_tree->delete(self->_tree, &node);
 }
 
 void map_contains(struct _map* self, const char* key)
@@ -113,6 +107,15 @@ bool map_set(struct _map* self, const char* key, void* value)
     return false;
 }
 
+static int map_compare(void* obj1, void* obj2)
+{
+    assert(obj1 != NULL && obj2 != NULL);
+
+    map_node_t node1 = (map_node_t)obj1;
+    map_node_t node2 = (map_node_t)obj2;
+    return strcmp(node1->key, node2->key);
+}
+
 bool map_init(struct _map* self, uint32_t obj_size)
 {
     assert(self != NULL);
@@ -129,6 +132,7 @@ bool map_init(struct _map* self, uint32_t obj_size)
     {
         return false;
     }
+    self->_tree->compare = map_compare;
 
     // -------------------- public --------------------
     // kernel
@@ -145,9 +149,8 @@ bool map_init(struct _map* self, uint32_t obj_size)
     self->size = map_size;
 
     // -------------------- default --------------------
-    self->compare = default_compare;
+    // self->compare = default_compare;
     self->print_obj = default_print_obj;
-    self->_tree->compare = self->compare;
 
     return true;
 }
@@ -157,7 +160,7 @@ bool map_destory(struct _map* self)
     self->clear(self);
     if(self->_tree != NULL)
     {
-        tree_rb_free(self->_tree);
+        tree_free(&self->_tree);
         self->_tree = NULL;
     }
     return true;