diff --git a/.gitignore b/.gitignore
index 0d28bdd..13b5060 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
-test.invodb
\ No newline at end of file
+test.invodb
+/cmake-build-debug/
+.idea
\ No newline at end of file
diff --git a/invodb/btree/btree.h b/invodb/btree/btree.h
index 78a2fd0..1a90982 100644
--- a/invodb/btree/btree.h
+++ b/invodb/btree/btree.h
@@ -18,11 +18,12 @@ public:
     bool exists(const KT &key);
     int getNodeSize();
     int find(const KT &key);
+    int findNode(const KT &key);
+    int firstNode();
     std::vector<KT> keySet();
     std::vector<std::pair<KT, int>> all();
     int size();
 private:
-    int findNode(const KT &key);
     void removeEntry(int curAdd, const KT& key, const int& pointer);
     bool canCoalesce(int curAdd, int sibAdd);
     void coalesce(int curAdd, int sibAdd);
@@ -473,5 +474,14 @@ std::vector<std::pair<KT, int>> BTree<KT, K_SIZE>::all() {
     return v;
 }
 
+template<typename KT, int K_SIZE>
+int BTree<KT, K_SIZE>::firstNode() {
+    auto p = BTreeNode<M_SIZE, KT, K_SIZE>::getNode(root);
+    while(!p->leaf) {
+        p = BTreeNode<M_SIZE, KT, K_SIZE>::getNode(p->linkSet[0]);
+    }
+    return p.address;
+}
+
 
 #endif //INVODB_BTREE_H
diff --git a/invodb/btree/node.h b/invodb/btree/node.h
index 9b8f056..da496c1 100644
--- a/invodb/btree/node.h
+++ b/invodb/btree/node.h
@@ -83,7 +83,7 @@ BTreeNode<M_SIZE, KT, K_SIZE>::BTreeNode(const int& address): address(address) {
 
 template<int M_SIZE, typename KT, int K_SIZE>
 BTreeNode<M_SIZE, KT, K_SIZE> *BTreeNode<M_SIZE, KT, K_SIZE>::getNode(const int &index) {
-    if(index < 4) {
+    if(index == 0) {
         throw "invalid address!";
     }
     static std::map<int, BTreeNode<M_SIZE, KT, K_SIZE>*> map;
@@ -96,6 +96,7 @@ BTreeNode<M_SIZE, KT, K_SIZE> *BTreeNode<M_SIZE, KT, K_SIZE>::getNode(const int
 
 template<int M_SIZE, typename KT, int K_SIZE>
 BTreeNode<M_SIZE, KT, K_SIZE> *BTreeNode<M_SIZE, KT, K_SIZE>::release(const int &index) {
+    PageManager::Instance().release(index);
     return nullptr;
 }
 
diff --git a/invodb/file/page_manager.cpp b/invodb/file/page_manager.cpp
index f4c911e..5c86110 100644
--- a/invodb/file/page_manager.cpp
+++ b/invodb/file/page_manager.cpp
@@ -3,17 +3,25 @@
 //
 
 #include "page_manager.h"
+#include "btree/list.h"
+
+List<int, 4>* PageManager::freeList = new List<int, 4>(1);
 
 int PageManager::loadDatabase(const char *filename) {
     Instance().stream.open(filename);
+    Instance().stream.seekp(0, std::ios::end);
+    int index = Instance().stream.tellp() / 1024;
+    if(index == 0) {
+        StoragePage(0).save();
+        StoragePage(1).save();
+        StoragePage(2).save();
+    }
     return 0;
 }
 
 StoragePage PageManager::getPage(const int &index) {
 
     if(cache.exist(index)) {
-        static int cnt = 0;
-        printf("%d\n", ++cnt);
         return cache.get(index);
     }
 
@@ -26,9 +34,7 @@ StoragePage PageManager::getPage(const int &index) {
 }
 
 void PageManager::setPage(const int &index, const StoragePage &page) {
-
     cache.put(index, page);
-
     stream.clear();
     stream.seekg(index * 1024);
     stream.write(page, 1024);
@@ -41,8 +47,15 @@ int PageManager::allocate() {
     return index;
 }
 
-void PageManager::release(const int &index) {
-
+void PageManager::release(const int &index, const bool &next) {
+    auto page = getPage(index);
+    freeList->insert(page.getAddress());
+    if(next) {
+        while(page.next()) {
+            freeList->insert(page.next());
+            page = getPage(page.next());
+        }
+    }
 }
 
 nlohmann::json PageManager::readJSONFromFile(const int &index) {
@@ -83,9 +96,6 @@ int PageManager::saveJSONToFile(const nlohmann::json& json) {
             page.save();
         }
     }
-
-
-
     return res;
 }
 
diff --git a/invodb/file/page_manager.h b/invodb/file/page_manager.h
index 0382015..d8f48f5 100644
--- a/invodb/file/page_manager.h
+++ b/invodb/file/page_manager.h
@@ -13,6 +13,9 @@
 #include "json/json.hpp"
 #include "models/cache.h"
 
+template<typename T, int T_SIZE>
+class List;
+
 class PageManager {
 public:
     static PageManager& Instance() {
@@ -23,15 +26,16 @@ public:
     StoragePage getPage(const int &index);
     void setPage(const int &index, const StoragePage &page);
     int allocate();
-    void release(const int &index);
+    void release(const int &index, const bool &next = true);
     int saveJSONToFile(const nlohmann::json& json);
     nlohmann::json readJSONFromFile(const int &index);
 private:
+    static List<int, 4> *freeList;
     std::map<int, StoragePage> map;
     std::fstream stream;
     LRUCache<int, StoragePage> cache;
     // 私有化实现单例
-    PageManager():cache(LRUCache<int, StoragePage>(50000)) {}
+    PageManager():cache(LRUCache<int, StoragePage>(1000)) {}
     ~PageManager() {}
     PageManager(const PageManager&);
     PageManager& operator=(const PageManager&);
diff --git a/invodb/models/collection.cpp b/invodb/models/collection.cpp
index 9b0cafe..5e0d87a 100644
--- a/invodb/models/collection.cpp
+++ b/invodb/models/collection.cpp
@@ -4,57 +4,26 @@
 
 #include "collection.h"
 
+BTree<std::string, 32> Collection::colList(2);
 std::map<std::string, Collection*> Collection::map;
-std::set<int> Collection::free;
 
 void Collection::loadCollections() {
-    // 前四页为集合信息页
-    for (int id = 0; id < 4; id++) {
-        StoragePage page = PageManager::Instance().getPage(id);
-        PageManager::Instance().setPage(id, page);
-        for (int i = 0; i < 32; i++) {
-            int p = i * 32;
-            int len = strlen(&page[p]);
-            std::string name(&page[p], len > 28 ? 28 : len);
-            int firstPage = page.getIntStartFrom(p + 28);
-            // if free
-            if (firstPage == 0) free.insert(id * 32 + i);
-            // not free
-            else map.insert(make_pair(name, new Collection(name, firstPage)));
-        }
+    int cnt = 0;
+    for(auto& key : colList.keySet()) {
+        map.insert(std::make_pair(key, new Collection(key, colList.find(key))));
+        cnt++;
     }
-    Logger::info<std::string, int>("Successfully load Collections: ", 128 - free.size());
+    Logger::info<std::string, int>("Successfully load Collections: ", cnt);
 }
 
 Collection& Collection::createCollection(const std::string &name) {
     // exist
     if(map.count(name) != 0) {
-        throw "collection has already exist";
+        return *map[name];
     }
-    // no free line
-    if(free.size() == 0) {
-        throw "you are reach the max limit count of collections";
-    }
-    int id = *free.begin();
-    free.erase(free.begin());
-
-    StoragePage page = PageManager::Instance().getPage(id / 32);
-    id %= 32;
-
-    StoragePage collectionPage = PageManager::Instance().getPage(PageManager::Instance().allocate());
-
-    if(name.size() > 28) {
-        throw "too long name of collection";
-    }
-
-    page.setStringStartFrom(id*32, name.c_str());
-    page.setIntStartFrom(id*32+28, collectionPage.getAddress());
-    page.save();
-
-    Collection *col = new Collection(name, collectionPage.getAddress());
-
+    colList.insert(name, PageManager::Instance().allocate());
+    Collection *col = new Collection(name, colList.find(name));
     map.insert(make_pair(name, col));
-
     return *col;
 }
 
@@ -68,8 +37,6 @@ Collection &Collection::getCollection(const std::string &name) {
 Collection::Collection(const std::string &name, const int &firstPage) {
     Logger::info<std::string, std::string>("load Collection: ", name);
     index = new BTree<std::string, 128>(firstPage);
-
-
     if(!index->exists("__INVO_ID__")) {
         index->insert("__INVO_ID__", PageManager::Instance().allocate());
     }
diff --git a/invodb/models/collection.h b/invodb/models/collection.h
index 7f11968..d98d75a 100644
--- a/invodb/models/collection.h
+++ b/invodb/models/collection.h
@@ -36,7 +36,7 @@ private:
     void removeIndex(const std::string indexName, bool indexValue, const int& address);
 
     static std::map<std::string, Collection*> map;
-    static std::set<int> free;
+    static BTree<std::string, 32> colList;
 
     BTree<std::string, 32> *uuid;
     BTree<std::string, 128> *index;