diff --git a/Database/Database.cpp b/Database/Database.cpp
index ade436d..875d140 100644
--- a/Database/Database.cpp
+++ b/Database/Database.cpp
@@ -562,7 +562,9 @@ Database::load()
 		return true;
 	}
 
-	bool flag = (this->vstree)->loadTree();
+	//TODO: acquire this arg from memory manager
+	unsigned vstree_cache = LRUCache::DEFAULT_CAPACITY;
+	bool flag = (this->vstree)->loadTree(vstree_cache);
 	if (!flag)
 	{
 		cout << "load tree error. @Database::load()" << endl;
@@ -806,9 +808,12 @@ Database::build(const string& _rdf_file)
 	string _entry_file = this->getSignatureBFile();
 
 	cout << "begin build VS-Tree on " << ret << "..." << endl;
-	//TODO: we can use larger buffer for vstree in building process, because it does not compete with others
+	//NOTICE: we can use larger buffer for vstree in building process, because it does not compete with others
 	//we only need to build vstree in this phase(no need for id tuples anymore)
-	(this->vstree)->buildTree(_entry_file);
+	//TODO: acquire this arg from memory manager
+	unsigned vstree_cache_size = 4 * LRUCache::DEFAULT_CAPACITY;
+	//BETTER: we should set the parameter according to current memory usage
+	(this->vstree)->buildTree(_entry_file, vstree_cache_size);
 
 	long tv_build_end = Util::get_cur_time();
 
diff --git a/VSTree/LRUCache.cpp b/VSTree/LRUCache.cpp
index 9b15054..ceac195 100644
--- a/VSTree/LRUCache.cpp
+++ b/VSTree/LRUCache.cpp
@@ -27,6 +27,8 @@ int LRUCache::DEFAULT_CAPACITY = 1 * 1000 * 1000;  //about 20G memory for vstree
 //int LRUCache::DEFAULT_CAPACITY = 1000;
 //NOTICE:10^6 is a good parameter, at most use 20G
 
+//NOTICE: it is ok to set it 4000000 when building!!!  better to adjust according to the current memory usage
+//also use 2000000 or smaller for query()
 LRUCache::LRUCache(int _capacity)
 {
 	//initialize the lock
@@ -39,7 +41,7 @@ LRUCache::LRUCache(int _capacity)
 	cout << "LRUCache initial..." << endl;
 	this->capacity = _capacity > 0 ? _capacity : LRUCache::DEFAULT_CAPACITY;
 
-	// TODO+DEBUG:it seems that a minium size is required, for example, multiple path down(the height?)
+	//DEBUG:it seems that a minium size is required, for example, multiple path down(the height?)
 	//at least 3*h
 	//
 	// we should guarantee the cache is big enough.
diff --git a/VSTree/VSTree.cpp b/VSTree/VSTree.cpp
index a2ee983..9fea1a9 100644
--- a/VSTree/VSTree.cpp
+++ b/VSTree/VSTree.cpp
@@ -160,14 +160,18 @@ void VSTree::retrieve(SPARQLquery& _query)
 //NOTICE:this can only be done by one thread
 //build the VSTree from the _entity_signature_file. 
 bool 
-VSTree::buildTree(std::string _entry_file_path)
+VSTree::buildTree(std::string _entry_file_path, int _cache_size)
 {
 	Util::logging("IN VSTree::buildTree");
+	
+	//NOTICE: entry buffer don't  need to store all entities, just loop, read and deal
+	//not so much memory: 2 * 10^6 * (4+800/8) < 1G
 
     // create the entry buffer and node buffer.
 	this->entry_buffer = new EntryBuffer(EntryBuffer::DEFAULT_CAPACITY);
 	//cout<<"entry buffer newed"<<endl;
-    this->node_buffer = new LRUCache(LRUCache::DEFAULT_CAPACITY);
+    this->node_buffer = new LRUCache(_cache_size);
+    //this->node_buffer = new LRUCache(LRUCache::DEFAULT_CAPACITY);
 
     // create the root node.
     //VNode* rootNodePtr = new VNode();
@@ -643,10 +647,11 @@ VSTree::saveTree()
 }
 
 bool 
-VSTree::loadTree()
+VSTree::loadTree(int _cache_size)
 {
 	cout << "load VSTree..." << endl;
-	(this->node_buffer) = new LRUCache(LRUCache::DEFAULT_CAPACITY);
+	(this->node_buffer) = new LRUCache(_cache_size);
+	//(this->node_buffer) = new LRUCache(LRUCache::DEFAULT_CAPACITY);
 	cout<<"LRU cache built"<<endl;
 
     bool flag = this->loadTreeInfo();
diff --git a/VSTree/VSTree.h b/VSTree/VSTree.h
index 8ab1c3b..9cedc2a 100644
--- a/VSTree/VSTree.h
+++ b/VSTree/VSTree.h
@@ -28,7 +28,7 @@ public:
     ~VSTree();
     int getHeight()const;
 	 //build the VSTree from the _entity_signature_file. 
-    bool buildTree(std::string _entity_signature_file);
+    bool buildTree(std::string _entity_signature_file, int _cache_size = -1);
     bool deleteTree();
 
 	//if the tree is empty
@@ -50,7 +50,7 @@ public:
 	//save the tree information to tree_info_file_path, and flush the tree nodes in memory to tree_node_file_path. 
     bool saveTree();
 	//load tree from tree_info_file_path and tree_node_file_path files. 
-    bool loadTree();
+    bool loadTree(int _cache_size = -1);
 	//get the tree's root node pointer. 
     VNode* getRoot();
 	//get the node pointer by its file line.