diff --git a/CMakeLists.txt b/CMakeLists.txt
index 373e4f7..6f18549 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -120,12 +120,13 @@ include(GNUInstallDirs)
 add_library(leveldb ""
         db/slotpage.h
         db/vlog.h
-        db/threadpool.h
         db/shared_lock.h
         db/vlog_set.cpp
         db/vlog_set.h
         db/vlog_gc.cpp
-        db/vlog_gc.h)
+        db/vlog_gc.h
+        db/gc_executor.cpp
+        db/gc_executor.h)
 target_sources(leveldb
         PRIVATE
         "${PROJECT_BINARY_DIR}/${LEVELDB_PORT_CONFIG_DIR}/port_config.h"
diff --git a/db/db_impl.cc b/db/db_impl.cc
index 4c0f2e5..7db4001 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -10,6 +10,7 @@
 #include <cstdio>
 #include <set>
 #include <string>
+#include <cstring>
 #include <vector>
 #include <iomanip>
 #include <iostream>
@@ -1188,7 +1189,7 @@ Status DBImpl::get_slot_num(const ReadOptions& options, const Slice& key,
 }
 
 Status DBImpl::Get_Fields(const ReadOptions& options, const Slice& key,
-                          FieldArray* fields) {
+                          FieldArray& fields) {
   // Todo(begin)
   size_t slot_num;
   // 从value中提取slot_num
@@ -1200,10 +1201,10 @@ Status DBImpl::Get_Fields(const ReadOptions& options, const Slice& key,
   struct slot_content sc;
   std::string vlog_value;
   slot_page_->get_slot(slot_num, &sc);
-  vlog_set_->get_value(sc.vlog_num, sc.value_offset, &vlog_value);
+  vlog_set_->get_value(sc, &vlog_value);
 
   std::cout << "value from value_log: " << key.ToString() << vlog_value << std::endl;
-  *fields = DeserializeValue(vlog_value);
+  DeserializeValue(fields, vlog_value);
   return Status::OK();
   // Todo(end)
 }
@@ -1212,12 +1213,15 @@ Status DBImpl::Get(const ReadOptions& options, const Slice& key,
                    std::string* value) {
   size_t slot_num;
   auto s = get_slot_num(options, key, &slot_num);
+  if (!s.ok()) {
+    return s;
+  }
 
   // TODO: search the slotpage and get value from vlog
   struct slot_content sc;
   std::string vlog_value;
   slot_page_->get_slot(slot_num, &sc);
-  vlog_set_->get_value(sc.vlog_num, sc.value_offset, &vlog_value);
+  vlog_set_->get_value(sc, &vlog_value);
   *value = vlog_value;
 
   return s;
@@ -1255,13 +1259,13 @@ void DBImpl::ReleaseSnapshot(const Snapshot* snapshot) {
 // Convenience methods
 Status DBImpl::Put_Fields(const WriteOptions& opt, const Slice& key,
                           const FieldArray& fields) {
-  // TODO(begin): allocate slot_num in slotpage and put value in vlog
   // 将字段数组序列化
-  std::string serialized_value = SerializeValue(fields);
+  std::string serialized_value;
   std::cout << "Put_Fields: " << key.ToString() << " " << serialized_value << std::endl;
   size_t slot_num = slot_page_->alloc_slot();
+  SerializeValue(fields, serialized_value, slot_num);
   struct slot_content sc;
-  vlog_set_->put_value(&sc.vlog_num, &sc.value_offset, serialized_value);
+  vlog_set_->put_value(sc, slot_num, serialized_value);
   slot_page_->set_slot(slot_num, &sc);
 
   char data[sizeof(size_t)];
@@ -1269,16 +1273,12 @@ Status DBImpl::Put_Fields(const WriteOptions& opt, const Slice& key,
   Slice slot_val(data, sizeof(data));
 
   return DB::Put(opt, key, slot_val);
-  // TODO(end)
 }
 
 Status DBImpl::Put(const WriteOptions& opt, const Slice& key, const Slice& val) {
-  // TODO: allocate slot_num in slotpage and put value in vlog
-
   size_t slot_num = slot_page_->alloc_slot();
-//  std::string slot_num_str((char *)&slot_num, sizeof(size_t));
   struct slot_content sc;
-  vlog_set_->put_value(&sc.vlog_num, &sc.value_offset, val);
+  vlog_set_->put_value(sc, slot_num, val);
   slot_page_->set_slot(slot_num, &sc);
 
   char data[sizeof(size_t)];
@@ -1291,10 +1291,14 @@ Status DBImpl::Put(const WriteOptions& opt, const Slice& key, const Slice& val)
 Status DBImpl::Delete(const WriteOptions& options, const Slice& key) {
   size_t slot_num;
   auto s = get_slot_num(ReadOptions(), key, &slot_num);
+  if (!s.ok()) {
+    return s;
+  }
 
   struct slot_content sc;
   slot_page_->get_slot(slot_num, &sc);
-  vlog_set_->del_value(sc.vlog_num, sc.value_offset);
+  vlog_set_->del_value(sc);
+  slot_page_->dealloc_slot(slot_num);
 
   return DB::Delete(options, key);
 }
@@ -1579,88 +1583,72 @@ void DBImpl::GetApproximateSizes(const Range* range, int n, uint64_t* sizes) {
 
   v->Unref();
 }
-// Todo(begin)
-// 反序列化函数，将字符串解码为字段数组
-FieldArray DBImpl::DeserializeValue(const std::string& value_str) {
-  // 存放解析后的字段数组
-  FieldArray fields;
-  // 将输入字符串转换为输入流 iss， 方便读取
-  std::istringstream iss(value_str);
-  std::string content;
-  // 临时存放读取的数据
-  char buffer[100];
-  // 读取长度（定长,16比特）
-  iss.read(buffer, 16);
-  buffer[16] = '\0';
-  size_t total_length = std::stoi(buffer);
-  //  std::cout << "读取到的总长度为： " << total_length << std::endl;
-  std::string value_content(value_str.begin() + 16, value_str.begin() + 16 + total_length);
-  //  std::cout << value_content << std::endl;
-  std::istringstream iss_content(value_content);
-  iss_content.read(buffer, sizeof(size_t));
-  buffer[sizeof(size_t)] = '\0';
-  std::string slot_num = buffer;
-  // 读取属性个数
-  iss_content.read(buffer, 16);
-  // 在第17个比特位处添加终结符，确保字符串以终结符结尾
-  buffer[16] = '\0';
-  // 将 buffer 中的内容转化为整数并赋值给 field_count
-  int field_count = std::stoi(buffer);
-  //  std::cout << "读取到的字段个数为： " << field_count << std::endl;
-
-  for (int i = 0; i < field_count; ++i) {
-    Field field;
-    // 读取属性名长度（定长,16比特）
-    iss_content.read(buffer, 16);
-    buffer[16] = '\0';
-    int name_length = std::stoi(buffer);
-    //    std::cout << "读取到的属性名长度为： " << name_length << std::endl;
-    // 读取属性名（变长）
-    field.name.resize(name_length);
-    iss_content.read(&field.name[0], name_length);
-    //    std::cout << "读取到的属性名为： " << field.name << std::endl;
-    // 读取属性值长度（定长,16比特）
-    iss_content.read(buffer, 16);
-    buffer[16] = '\0';
-    int value_length = std::stoi(buffer);
-    //    std::cout << "读取到的属性值长度为： " << value_length << std::endl;
-    // 读取属性值（变长）
-    field.value.resize(value_length);
-    iss_content.read(&field.value[0], value_length);
-    //    std::cout << "读取到的属性值为： " << field.value << std::endl;
-    fields.push_back(field);
-  }
-  return fields;
+
+//using FieldArray = std::vector<Field>;
+//struct Field { std::string name; std::string value; };
+void DBImpl::DeserializeValue(FieldArray& fields, const std::string& value_str) {
+  // single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+  // single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+  const char *value_data = value_str.c_str();
+  const size_t value_len = value_str.size();
+  size_t attr_off = sizeof(uint16_t);
+
+  while (attr_off < value_len) {
+    uint8_t attr_name_len = *(uint8_t *)(value_data+attr_off);
+    attr_off += sizeof(uint8_t);
+    auto attr_name = std::string(value_data+attr_off, attr_name_len);
+    attr_off += attr_name_len;
+
+    uint16_t attr_len = *(uint16_t *)(value_data+attr_off);
+    attr_off += sizeof(uint16_t);
+    auto attr_value = std::string(value_data+attr_off, attr_len);
+    attr_off += attr_len;
+
+    fields.push_back({attr_name, attr_value});
+  }
+
+  assert(attr_off == value_len);
 }
-// Todo(end)
-// Todo(begin)
-// 序列化函数，将字段数组序列化为字符串
-std::string DBImpl::SerializeValue(const FieldArray& fields) {
-  // 创建并初始化一个字符串流 oss,用于逐步构建最终的序列化字符串
-  std::ostringstream oss_temp;
-  std::string slot_num = "slot_num";
-  oss_temp << std::setw(sizeof(size_t)) << std::setfill('0') << slot_num;
-  // 写入属性个数（定长,16比特），使用std::setw(16)设置宽度，使用std::setfull(0)设置填充字符，将字段数组的大小写入oss中
-  oss_temp << std::setw(16) << std::setfill('0') << fields.size();
+
+// 序列化函数，将字段数组序列化为字符串+
+//using FieldArray = std::vector<Field>;
+//struct Field { std::string name; std::string value; };
+void DBImpl::SerializeValue(const FieldArray& fields, std::string &value, size_t slot_num) {
+  // single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+  // single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+  std::string tmp_value;
+  uint16_t value_size = sizeof(uint16_t);
+  uint16_t field_nums = 0;
   for (const auto& field : fields) {
-    // 写入属性名长度（定长,16比特）
-    oss_temp << std::setw(16) << std::setfill('0') << field.name.size();
-    // 写入属性名（变长）
-    oss_temp << field.name;
-    // 写入属性值长度（定长,16比特）
-    oss_temp << std::setw(16) << std::setfill('0') << field.value.size();
-    // 写入属性值（变长）
-    oss_temp << field.value;
-  }
-  std::string temp_str = oss_temp.str();
-  size_t value_length = temp_str.size();
-
-  std::ostringstream oss;
-  oss << std::setw(16) << std::setfill('0') << value_length;
-  oss << temp_str;
-  return oss.str();
+    const uint8_t attr_name_len = field.name.size();
+    const uint16_t attr_value_len = field.value.size();
+    const size_t attr_size = attr_name_len + attr_value_len + sizeof(uint8_t) + sizeof(uint16_t);
+    char attr_data[attr_size];
+
+    size_t off = 0;
+    memcpy(attr_data+off, &attr_name_len, sizeof(uint8_t));
+    off += sizeof(uint8_t);
+    memcpy(attr_data+off, field.name.c_str(), attr_name_len);
+    off += attr_name_len;
+    memcpy(attr_data+off, &attr_value_len, sizeof(uint16_t));
+    off += sizeof(uint16_t);
+    memcpy(attr_data+off, field.value.c_str(), attr_value_len);
+    off += attr_value_len;
+
+    assert(off == attr_size);
+    tmp_value += std::string(attr_data, attr_size);
+    value_size += attr_size;
+    field_nums ++;
+  }
+
+  char value_data[value_size];
+  memcpy(value_data, &value_size, sizeof(uint16_t));
+  memcpy(value_data+sizeof(uint16_t), tmp_value.c_str(), tmp_value.size());
+
+  assert(sizeof(uint16_t) + tmp_value.size() == value_size);
+  value = std::string(value_data, value_size);
 }
-// Todo(end)
+
 // Default implementations of convenience methods that subclasses of DB
 // can call if they wish
 Status DB::Put(const WriteOptions& opt, const Slice& key, const Slice& value) {
diff --git a/db/db_impl.h b/db/db_impl.h
index 1f77d07..68c8320 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -53,7 +53,7 @@ class DBImpl : public DB {
              std::string* value) override;
   // Todo(begin)
   Status Get_Fields(const ReadOptions& options, const Slice& key,
-                   FieldArray* fields) override;
+                   FieldArray& fields) override;
   // Todo(end)
   Iterator* NewIterator(const ReadOptions&) override;
   const Snapshot* GetSnapshot() override;
@@ -91,8 +91,8 @@ class DBImpl : public DB {
   // TODO(begin)
   SlotPage *slot_page_;
   VlogSet *vlog_set_;
-  static std::string SerializeValue(const FieldArray& fields);
-  static FieldArray DeserializeValue(const std::string& value_str);
+  static void SerializeValue(const FieldArray& fields, std::string &value, size_t slot_num);
+  static void DeserializeValue(FieldArray& fields, const std::string& value_str);
   // TODO(end)
   // Information for a manual compaction
   struct ManualCompaction {
diff --git a/db/gc_executor.cpp b/db/gc_executor.cpp
new file mode 100644
index 0000000..2091e9b
--- /dev/null
+++ b/db/gc_executor.cpp
@@ -0,0 +1,74 @@
+//
+// Created by 马也驰 on 2025/1/3.
+//
+
+#include "gc_executor.h"
+#include "vlog_set.h"
+#include "vlog_gc.h"
+
+
+ void gc_executor::exec_gc(VlogGC *vlog_gc_, size_t old_vlog_num, size_t new_vlog_num) {
+  auto vlog_set = vlog_gc_->vlog_set;
+  auto slot_page_ = vlog_gc_->slot_page_;
+
+  vlog_set->mtx.lock();
+  auto old_vlog_name = vlog_set->get_vlog_name(old_vlog_num);
+  auto new_vlog_name = vlog_set->get_vlog_name(new_vlog_num);
+  auto old_vlog_info = vlog_set->get_vlog_info(old_vlog_num);
+  auto new_vlog_info = vlog_set->get_vlog_info(new_vlog_num);
+  auto old_vlog_handler = vlog_set->get_vlog_handler(old_vlog_num);
+  auto new_vlog_handler = vlog_set->get_vlog_handler(new_vlog_num);
+
+  old_vlog_info->vlog_info_latch_.lock();
+  old_vlog_handler->vlog_latch_.soft_lock();
+  new_vlog_info->vlog_info_latch_.lock();
+  new_vlog_handler->vlog_latch_.hard_lock();
+  vlog_set->mtx.unlock();
+
+  auto old_vlog = std::fstream(old_vlog_name, std::ios::in | std::ios::out);
+  auto new_vlog = std::fstream(new_vlog_name, std::ios::in | std::ios::out);
+
+  char old_vlog_buff[VLOG_SIZE];
+  char new_vlog_buff[VLOG_SIZE];
+  old_vlog.seekp(0);
+  old_vlog.read(old_vlog_buff, VLOG_SIZE);
+
+  size_t value_nums = old_vlog_info->value_nums;
+  size_t ovb_off = 2 * sizeof(size_t);
+  size_t nvb_off = 2 * sizeof(size_t);
+  size_t new_vlog_value_nums = 0;
+  for (auto i = 0; i < value_nums; i++) {
+    char *value = &old_vlog_buff[ovb_off];
+    uint16_t value_len = get_value_len(value);
+    size_t slot_num = get_value_slotnum(value);
+    if (!value_deleted(value_len)) {
+      memcpy(&new_vlog_buff[nvb_off], &old_vlog_buff[ovb_off], value_len);
+      memcpy(&new_vlog_buff[nvb_off+sizeof(uint16_t)], &(new_vlog_info->vlog_num), sizeof(size_t));
+      struct slot_content scn(new_vlog_info->vlog_num, nvb_off);
+      slot_page_->set_slot(slot_num, &scn);
+      nvb_off += value_len;
+      new_vlog_value_nums ++;
+    }
+    ovb_off += value_len;
+  }
+  new_vlog_info->value_nums = new_vlog_value_nums;
+  new_vlog_info->curr_size = nvb_off;
+  memcpy(new_vlog_buff, &nvb_off, sizeof(size_t));
+  memcpy(&new_vlog_buff[sizeof(size_t)], &new_vlog_value_nums, sizeof(size_t));
+  new_vlog.seekp(0);
+  new_vlog.write(new_vlog_buff, VLOG_SIZE);
+  new_vlog.flush();
+
+  old_vlog.close();
+  new_vlog.close();
+
+  old_vlog_info->vlog_valid_ = false;
+  vlog_set->remove_old_vlog(old_vlog_num);
+
+  old_vlog_info->vlog_info_latch_.unlock();
+  old_vlog_handler->vlog_latch_.soft_unlock();
+  new_vlog_info->vlog_info_latch_.unlock();
+  new_vlog_handler->vlog_latch_.hard_unlock();
+
+//  vlog_gc_->gc_counter_decrement();
+}
diff --git a/db/gc_executor.h b/db/gc_executor.h
new file mode 100644
index 0000000..3c5af50
--- /dev/null
+++ b/db/gc_executor.h
@@ -0,0 +1,40 @@
+//
+// Created by 马也驰 on 2025/1/3.
+//
+
+#ifndef LEVELDB_GC_EXECUTOR_H
+#define LEVELDB_GC_EXECUTOR_H
+
+#include <cstdlib>
+#include <string>
+
+
+class VlogGC;
+
+class gc_executor {
+ public:
+  explicit gc_executor() {}
+
+  ~gc_executor() = default;
+
+ public:
+  static void exec_gc(VlogGC *vlog_gc_, size_t old_vlog_num, size_t new_vlog_num);
+
+ private:
+  static inline bool value_deleted(uint16_t value_len) {
+    return !(value_len >> 15);
+  }
+  static inline uint16_t get_value_len(char *value) {
+    uint16_t value_len;
+    memcpy(&value_len, value, sizeof(uint16_t));
+    return value_len;
+  }
+  static inline size_t get_value_slotnum(char *value) {
+    size_t slot_num;
+    memcpy(&slot_num, &value[sizeof(uint16_t)], sizeof(size_t));
+    return slot_num;
+  }
+
+};
+
+#endif  // LEVELDB_GC_EXECUTOR_H
diff --git a/db/shared_lock.h b/db/shared_lock.h
index 0d90490..083a1a7 100644
--- a/db/shared_lock.h
+++ b/db/shared_lock.h
@@ -45,8 +45,7 @@ class SharedLock {
   std::mutex read_latch_; // indicate if any read is proceeding
   std::mutex read_count_latch_;
   volatile size_t read_count_;
-  std::mutex write_latch_;
-  //  volatile size_t write_count_;
+  std::mutex write_latch_;  // indicate if any write is proceeding
 };
 
 #endif  // LEVELDB_SHARED_LOCK_H
diff --git a/db/slotpage.h b/db/slotpage.h
index 023ce60..b32fcd4 100644
--- a/db/slotpage.h
+++ b/db/slotpage.h
@@ -15,6 +15,8 @@
 #include <iostream>
 #include <unordered_map>
 
+// bitmap: || bitmap_size(size_t) | first_empty_slot(size_t) || bits... |
+
 #define BITMAP_SIZE 8192
 #define BITS_PER_BYTE 8
 
@@ -183,6 +185,69 @@ public:
     first_empty_slot = 0;
   }
 
+  BitMap(const std::string &dbname) {
+    name = dbname + "_bitmap";
+    auto bitmap_handler = std::fstream(name, std::ios::in | std::ios::out);
+    if (!bitmap_handler.is_open()) {
+      // 文件不存在，尝试创建
+      bitmap_handler = std::fstream(name, std::ios::out);
+      bitmap_handler.close();
+      // 重新以读写模式打开
+      bitmap_handler = std::fstream(name, std::ios::in | std::ios::out);
+      bitmap_handler.seekp(0);
+      size_t tmp[2] = {2*sizeof(size_t), 0};
+      bitmap_handler.write(reinterpret_cast<const char*>(tmp), sizeof(tmp));
+      bitmap_handler.close();
+
+      // init bitmap
+      char *bitmap = static_cast<char*>(malloc(BITMAP_SIZE*sizeof(char)));
+      memset(bitmap, 0, BITMAP_SIZE * sizeof(char));
+      bitmaps_.push_back(bitmap);
+      size = BITMAP_SIZE;
+      first_empty_slot = 0;
+    } else {
+      // read in bitmap content
+      size_t bitmap_header[2];
+      bitmap_handler.seekp(0);
+      bitmap_handler.read(reinterpret_cast<char*>(bitmap_header), 2*sizeof(size_t));
+      this->first_empty_slot = bitmap_header[1];
+      this->size = bitmap_header[0];
+
+      const size_t page_num = (size - 2*sizeof(size_t)) / BITMAP_SIZE;
+      for (auto i = 0; i < page_num; i++) {
+        char *bitmap = static_cast<char*>(malloc(BITMAP_SIZE*sizeof(char)));
+        bitmap_handler.seekp(2*sizeof(size_t) + i*BITMAP_SIZE);
+        bitmap_handler.read(bitmap, BITMAP_SIZE);
+        bitmaps_.push_back(bitmap);
+      }
+
+      // init bitmap
+      if (page_num == 0) {
+        char *bitmap = static_cast<char*>(malloc(BITMAP_SIZE*sizeof(char)));
+        memset(bitmap, 0, BITMAP_SIZE * sizeof(char));
+        bitmaps_.push_back(bitmap);
+        size = BITMAP_SIZE;
+        first_empty_slot = 0;
+      }
+    }
+  }
+
+  ~BitMap() {
+    auto bitmap_handler = std::fstream(name, std::ios::in | std::ios::out);
+    assert(bitmap_handler.is_open());
+    size_t tmp[2] = {size, first_empty_slot};
+    bitmap_handler.seekp(0);
+    bitmap_handler.write(reinterpret_cast<const char*>(tmp), sizeof(tmp));
+    size_t off = 2 * sizeof(size_t);
+    for (auto bitmap : bitmaps_) {
+      bitmap_handler.seekp(off);
+      bitmap_handler.write(bitmap, BITMAP_SIZE);
+      off += BITMAP_SIZE;
+    }
+    assert(off == size);
+    bitmap_handler.flush();
+  }
+
   /** methods for test **/
   void show_allocated_slot() {
     for (int i = 0; i < this->size; i++) {
@@ -284,6 +349,7 @@ private:
   }
 
 private:
+  std::string name;
   std::vector<char *> bitmaps_;
   size_t size;
   size_t first_empty_slot;
@@ -299,7 +365,7 @@ class SlotPage {
 public:
   SlotPage(const std::string &dbname) {
     slotpage_fname = slotpage_handler_name(dbname);
-    bitmap = new BitMap();
+    bitmap = new BitMap(dbname);
     slotcache = new SlotCache(slotpage_fname);
     assert(slotcache);
   }
diff --git a/db/threadpool.h b/db/threadpool.h
deleted file mode 100644
index 00d861d..0000000
--- a/db/threadpool.h
+++ /dev/null
@@ -1,67 +0,0 @@
-//
-// Created by 马也驰 on 2024/12/28.
-//
-
-#ifndef LEVELDB_THREADPOOL_H
-#define LEVELDB_THREADPOOL_H
-
-
-#include <iostream>
-#include <vector>
-#include <thread>
-#include <queue>
-#include <functional>
-#include <condition_variable>
-#include <atomic>
-
-class ThreadPool {
- public:
-  explicit ThreadPool(size_t numThreads) : stop(false) {
-    for (size_t i = 0; i < numThreads; ++i) {
-      workers.emplace_back([this]() {
-        while (true) {
-          std::function<void()> task;
-          {
-            std::unique_lock<std::mutex> lock(queueMutex);
-            condition.wait(lock, [this]() { return stop || !tasks.empty(); });
-
-            if (stop && tasks.empty()) return;
-
-            task = std::move(tasks.front());
-            tasks.pop();
-          }
-          task();
-        }
-      });
-    }
-  }
-
-  ~ThreadPool() {
-    {
-      std::unique_lock<std::mutex> lock(queueMutex);
-      stop = true;
-    }
-    condition.notify_all();
-    for (std::thread &worker : workers) {
-      worker.join();
-    }
-  }
-
-  void enqueue(std::function<void()> task) {
-    {
-      std::unique_lock<std::mutex> lock(queueMutex);
-      tasks.push(std::move(task));
-    }
-    condition.notify_one();
-  }
-
- private:
-  std::vector<std::thread> workers;
-  std::queue<std::function<void()>> tasks;
-  std::mutex queueMutex;
-  std::condition_variable condition;
-  std::atomic<bool> stop;
-};
-
-
-#endif  // LEVELDB_THREADPOOL_H
diff --git a/db/vlog.h b/db/vlog.h
index b48d72b..9c504df 100644
--- a/db/vlog.h
+++ b/db/vlog.h
@@ -12,20 +12,23 @@
 #include <cstdio>
 
 
-#include "../db/threadpool.h"
 #include "../include/leveldb/slice.h"
 #include "../db/slotpage.h"
 #include "../db/shared_lock.h"
 
-// config file: | vlog_nums_(size_t) | vlog_1_name | vlog_2_name | ... |
-// vlog: | curr_size(size_t) | value_nums(size_t) | value1 | value2 | ... |
-// value: | value_size(uint16_t) | slot_num(size_t) | field_nums(uint16_t) ｜ value |
+// config file: || vlog_nums_(size_t) || vlog_1_num(size_t) | vlog_2_num(size_t) | ... |
+// vlog: || curr_size(size_t) | value_nums(size_t) || value1 | value2 | ... |
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+
+// {field_nums(uint16_t), attr1, attr2, ... } is wrapped/unwrapped in dm_impl
+// || value_size(uint16_t) | slot_num(size_t) ||      VALUE: {field_nums(uint16_t), attr1, attr2, ... }     | is wrapped/unwrapped in vlog_set
+
 
 #define vlog_num_size     sizeof(size_t)
-#define vlog_name_size    256
 #define KiB               1024
 #define MiB               1024*KiB
-#define VLOG_SIZE         32*MiB
+#define VLOG_SIZE         1*MiB     // origin: 32*MiB
 #define GC_THREDHOLD      0.5
 
 #define VALUE_BUFF_SIZE   0x7fff  // value size cannot exceed this number
@@ -46,18 +49,22 @@
 //  }
 //};
 
+
 struct vlog_info {
   std::mutex vlog_info_latch_; // 保护对vlog_info本身的并发修改
   size_t vlog_num;
   size_t vlog_num_for_gc; // set when start gc
-  bool vlog_valid_;
+  bool processing_gc;; // init to be false, set as true when processing gc
+  bool vlog_valid_; // init to be true, set as false after deleted
   size_t discard;
   size_t value_nums;
   size_t curr_size;
-  vlog_info(size_t vlog_num) : vlog_valid_(true), discard(0), value_nums(0),
-                                vlog_num(vlog_num), curr_size(2*sizeof(size_t)) {}
-  vlog_info(size_t vlog_num, size_t value_nums, size_t curr_size) : vlog_valid_(true), discard(0), value_nums(value_nums),
-                                                                    vlog_num(vlog_num), curr_size(curr_size) {}
+  vlog_info(size_t vlog_num) : processing_gc(false), discard(0), value_nums(0),
+                                vlog_num(vlog_num), curr_size(2*sizeof(size_t)), vlog_valid_(true) {}
+  vlog_info(size_t vlog_num, size_t value_nums, size_t curr_size) : processing_gc(false),
+                                                                    discard(0), value_nums(value_nums),
+                                                                    vlog_num(vlog_num), curr_size(curr_size),
+                                                                    vlog_valid_(true) {}
 };
 
 struct vlog_handler {
diff --git a/db/vlog_gc.cpp b/db/vlog_gc.cpp
index 8555b63..d7bdca0 100644
--- a/db/vlog_gc.cpp
+++ b/db/vlog_gc.cpp
@@ -4,65 +4,196 @@
 
 #include "vlog_gc.h"
 #include "../db/vlog_set.h"
+#include <thread>
+#include <utility>
+
+
+struct executor_param {
+  VlogGC *vg;
+  size_t old_vlog_num;
+  size_t new_vlog_num;
+};
+
+std::mutex map_latch_;
+std::unordered_map<size_t, struct executor_param> executor_params_map_;
+std::unordered_map<size_t, VlogGC *> vlog_gc_map_;
+
+
+void test_func() {
+  int nums[4] = {1, 2, 3, 4};
+  for (int i = 0; i < 4; i++) {
+    nums[i] ++;
+  }
+}
+
+void add_executor_params(size_t gc_num, struct executor_param &ep) {
+  map_latch_.lock();
+  executor_params_map_[gc_num] = ep;
+  map_latch_.unlock();
+}
+
+struct executor_param get_executor_params(size_t gc_num) {
+  map_latch_.lock();
+  auto ep = executor_params_map_[gc_num];
+  map_latch_.unlock();
+  return ep;
+}
+
+void del_executor_params(size_t gc_num) {
+  map_latch_.lock();
+  executor_params_map_.erase(gc_num);
+  map_latch_.unlock();
+}
+
+void add_vlog_gc(size_t gc_num, VlogGC *vg) {
+  map_latch_.lock();
+  vlog_gc_map_[gc_num] = vg;
+  map_latch_.unlock();
+}
+
+VlogGC * get_vlog_gc(size_t gc_num) {
+  map_latch_.lock();
+  auto vg = vlog_gc_map_[gc_num];
+  map_latch_.unlock();
+  return vg;
+}
+
+void del_vlog_gc(size_t gc_num) {
+  map_latch_.lock();
+  vlog_gc_map_.erase(gc_num);
+  map_latch_.unlock();
+}
+
+// 函数：增加 counter
+void VlogGC::gc_counter_increment() {
+  vlog_set->counter_latch_.lock();
+  ++vlog_set->counter;                             // 增加 counter
+  std::cout << "Increment: Counter incremented to " << vlog_set->counter << "\n";
+  vlog_set->counter_latch_.unlock();
+}
+
+// 函数：减少 counter
+void VlogGC::gc_counter_decrement() {
+  vlog_set->counter_latch_.lock();
+  --vlog_set->counter;                             // 减少 counter
+  std::cout << "Decrement: Counter decremented to " << vlog_set->counter << "\n";
+
+  if (vlog_set->counter == 0) {
+    // 如果 counter 为 0
+    vlog_set->finished_latch_.lock();
+    vlog_set->finished = true;                   // 设置完成标志
+    vlog_set->finished_latch_.unlock();
+  }
+  vlog_set->counter_latch_.unlock();
+}
 
 
 void VlogGC::do_gc(size_t old_vlog_num, size_t new_vlog_num) {
-  thread_pool_->enqueue([this, old_vlog_num, new_vlog_num]()
-                        { this->exec_gc(old_vlog_num, new_vlog_num); });
+  gc_counter_increment();
+  size_t _gc_num_ = get_gc_num();
+
+  struct executor_param ep = {this, old_vlog_num, new_vlog_num};
+  add_executor_params(_gc_num_, ep);
+  add_vlog_gc(_gc_num_, this);
+
+  std::thread gc_thread([_gc_num_]() mutable {
+    auto _vlog_gc_ = get_vlog_gc(_gc_num_);
+    assert(_vlog_gc_ != nullptr);
+    _vlog_gc_->exec_gc(_gc_num_);
+  });
+
 }
 
-void VlogGC::exec_gc(size_t old_vlog_num, size_t new_vlog_num) {
-  auto old_vlog_name = vlog_set->get_vlog_name(old_vlog_num);
-  auto new_vlog_name = vlog_set->get_vlog_name(new_vlog_num);
-  auto old_vlog_info = vlog_set->get_vlog_info(old_vlog_num);
-  auto new_vlog_info = vlog_set->get_vlog_info(new_vlog_num);
-  auto old_vlog_handler = vlog_set->get_vlog_handler(old_vlog_num);
-  auto new_vlog_handler = vlog_set->get_vlog_handler(new_vlog_num);
-
-  old_vlog_handler->vlog_latch_.soft_lock();
-  new_vlog_info->vlog_info_latch_.lock();
-  new_vlog_handler->vlog_latch_.hard_lock();
-
-  auto old_vlog = std::fstream(old_vlog_name, std::ios::in | std::ios::out);
-  auto new_vlog = std::fstream(new_vlog_name, std::ios::in | std::ios::out);
-
-  char old_vlog_buff[VLOG_SIZE];
-  char new_vlog_buff[VLOG_SIZE];
-  old_vlog.seekp(0);
-  old_vlog.read(old_vlog_buff, VLOG_SIZE);
-//  memcpy(new_vlog_buff, &value_nums, sizeof(size_t));
-
-  size_t value_nums = old_vlog_info->value_nums;
-  size_t ovb_off = 2 * sizeof(size_t);
-  size_t nvb_off = 2 * sizeof(size_t);
-  size_t new_vlog_value_nums = 0;
-  for (auto i = 0; i < value_nums; i++) {
-    char *value = &old_vlog_buff[ovb_off];
-    uint16_t value_len = get_value_len(value);
-    size_t slot_num = get_value_slotnum(value);
-    if (!value_deleted(value_len)) {
-      memcpy(&new_vlog_buff[nvb_off], &old_vlog_buff[ovb_off], value_len);
-      struct slot_content scn(new_vlog_info->vlog_num, nvb_off);
-      slot_page_->set_slot(slot_num, &scn);
-      nvb_off += value_len;
-      new_vlog_value_nums ++;
-    }
-    ovb_off += value_len;
+
+void VlogGC::exec_gc(size_t gc_num_) {
+  // FIXME: might break, due to unknown concurrency problem
+  curr_thread_nums_latch_.lock();
+  curr_thread_nums_ ++;
+  if (curr_thread_nums_ >= max_thread_nums_) {
+    full_latch_.lock();
   }
-  new_vlog_info->value_nums = value_nums;
-  new_vlog_info->curr_size = nvb_off;
-  memcpy(new_vlog_buff, &nvb_off, sizeof(size_t));
-  memcpy(&new_vlog_buff[sizeof(size_t)], &new_vlog_value_nums, sizeof(size_t));
-  new_vlog.write(new_vlog_buff, VLOG_SIZE);
-  new_vlog.flush();
+  curr_thread_nums_latch_.unlock();
+
 
-  old_vlog.close();
-  new_vlog.close();
+  // start gc process
+  auto ep = get_executor_params(gc_num_);
+  gc_executor::exec_gc(ep.vg, ep.old_vlog_num, ep.new_vlog_num);
+//  test_func();
 
-  old_vlog_handler->vlog_latch_.soft_unlock();
-  new_vlog_info->vlog_info_latch_.unlock();
-  new_vlog_handler->vlog_latch_.hard_unlock();
+  curr_thread_nums_latch_.lock();
+  if (curr_thread_nums_ >= max_thread_nums_) {
+    full_latch_.unlock();
+  }
+  curr_thread_nums_ --;
+  curr_thread_nums_latch_.unlock();
 
-  vlog_set->remove_old_vlog(old_vlog_num);
+  gc_counter_decrement();
+  del_executor_params(gc_num_);
+  del_vlog_gc(gc_num_);
 }
 
+// vlog: || curr_size(size_t) | value_nums(size_t) || value1 | value2 | ... |
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+//void VlogGC::exec_gc(size_t old_vlog_num, size_t new_vlog_num) {
+//  vlog_set->mtx.lock();
+//  auto old_vlog_name = vlog_set->get_vlog_name(old_vlog_num);
+//  auto new_vlog_name = vlog_set->get_vlog_name(new_vlog_num);
+//  auto old_vlog_info = vlog_set->get_vlog_info(old_vlog_num);
+//  auto new_vlog_info = vlog_set->get_vlog_info(new_vlog_num);
+//  auto old_vlog_handler = vlog_set->get_vlog_handler(old_vlog_num);
+//  auto new_vlog_handler = vlog_set->get_vlog_handler(new_vlog_num);
+//
+//  old_vlog_info->vlog_info_latch_.lock();
+//  old_vlog_handler->vlog_latch_.soft_lock();
+//  new_vlog_info->vlog_info_latch_.lock();
+//  new_vlog_handler->vlog_latch_.hard_lock();
+//  vlog_set->mtx.unlock();
+//
+//  auto old_vlog = std::fstream(old_vlog_name, std::ios::in | std::ios::out);
+//  auto new_vlog = std::fstream(new_vlog_name, std::ios::in | std::ios::out);
+//
+//  char old_vlog_buff[VLOG_SIZE];
+//  char new_vlog_buff[VLOG_SIZE];
+//  old_vlog.seekp(0);
+//  old_vlog.read(old_vlog_buff, VLOG_SIZE);
+//
+//  size_t value_nums = old_vlog_info->value_nums;
+//  size_t ovb_off = 2 * sizeof(size_t);
+//  size_t nvb_off = 2 * sizeof(size_t);
+//  size_t new_vlog_value_nums = 0;
+//  for (auto i = 0; i < value_nums; i++) {
+//    char *value = &old_vlog_buff[ovb_off];
+//    uint16_t value_len = get_value_len(value);
+//    size_t slot_num = get_value_slotnum(value);
+//    if (!value_deleted(value_len)) {
+//      memcpy(&new_vlog_buff[nvb_off], &old_vlog_buff[ovb_off], value_len);
+//      memcpy(&new_vlog_buff[nvb_off+sizeof(uint16_t)], &(new_vlog_info->vlog_num), sizeof(size_t));
+//      struct slot_content scn(new_vlog_info->vlog_num, nvb_off);
+//      slot_page_->set_slot(slot_num, &scn);
+//      nvb_off += value_len;
+//      new_vlog_value_nums ++;
+//    }
+//    ovb_off += value_len;
+//  }
+//  new_vlog_info->value_nums = new_vlog_value_nums;
+//  new_vlog_info->curr_size = nvb_off;
+//  memcpy(new_vlog_buff, &nvb_off, sizeof(size_t));
+//  memcpy(&new_vlog_buff[sizeof(size_t)], &new_vlog_value_nums, sizeof(size_t));
+//  new_vlog.seekp(0);
+//  new_vlog.write(new_vlog_buff, VLOG_SIZE);
+//  new_vlog.flush();
+//
+//  old_vlog.close();
+//  new_vlog.close();
+//
+//  old_vlog_info->vlog_valid_ = false;
+//  vlog_set->remove_old_vlog(old_vlog_num);
+//
+//  old_vlog_info->vlog_info_latch_.unlock();
+//  old_vlog_handler->vlog_latch_.soft_unlock();
+//  new_vlog_info->vlog_info_latch_.unlock();
+//  new_vlog_handler->vlog_latch_.hard_unlock();
+//
+//}
+//
diff --git a/db/vlog_gc.h b/db/vlog_gc.h
index cbd1308..e49c197 100644
--- a/db/vlog_gc.h
+++ b/db/vlog_gc.h
@@ -9,19 +9,27 @@
 #include <string>
 #include <mutex>
 #include "../db/slotpage.h"
-#include "../db/threadpool.h"
 #include "../db/vlog.h"
+#include "../db/gc_executor.h"
 
 // 前向声明 VlogSet
 class VlogSet;
 
 class VlogGC {
+#define THREAD_NUM  8
+friend class gc_executor;
+
  public:
-  VlogGC(SlotPage *s, VlogSet *vs) : slot_page_(s), vlog_set(vs) {}
+  VlogGC(SlotPage *s, VlogSet *vs) : slot_page_(s), vlog_set(vs),max_thread_nums_(THREAD_NUM),
+                                     curr_thread_nums_(0), gc_num(0) {}
+  ~VlogGC() {}
+
   void do_gc(size_t old_vlog_num, size_t new_vlog_num);
 
  private:
-  void exec_gc(size_t old_vlog_num, size_t new_vlog_num);
+  void exec_gc(size_t gc_num_);
+  void gc_counter_increment();
+  void gc_counter_decrement();
 
   inline bool value_deleted(uint16_t value_len) {
     return !(value_len >> 15);
@@ -36,10 +44,24 @@ class VlogGC {
     memcpy(&slot_num, &value[sizeof(uint16_t)], sizeof(size_t));
     return slot_num;
   }
+  inline size_t get_gc_num() {
+    gc_num_latch_.lock();
+    size_t _gc_num_ = gc_num ++;
+    gc_num_latch_.unlock();
+    return _gc_num_;
+  }
 
   SlotPage *slot_page_;
-  ThreadPool *thread_pool_;
   VlogSet *vlog_set;  // 仅声明为指针，具体定义放在 vlog_gc.cpp
+
+  // NOTE: threadpool
+  std::mutex full_latch_; // indicate thread pool is full when set as locked
+  size_t max_thread_nums_;
+  std::mutex curr_thread_nums_latch_;
+  size_t curr_thread_nums_;
+
+  std::mutex gc_num_latch_;
+  size_t gc_num;
 };
 
 
diff --git a/db/vlog_set.cpp b/db/vlog_set.cpp
index 84793bf..0f4ed8f 100644
--- a/db/vlog_set.cpp
+++ b/db/vlog_set.cpp
@@ -4,6 +4,7 @@
 
 #include "vlog_set.h"
 #include "../db/vlog_gc.h"
+#include <thread>
 
 
 // config file: | vlog_nums_(size_t) | vlog_1_num(size_t) | vlog_2_num(size_t) | ... |
@@ -53,7 +54,6 @@ VlogSet::VlogSet(std::string dbname, VlogGC *vlog_gc) : dbname(dbname), vlog_gc(
     }
   }
 
-
   if (!this->config_file_->is_open()) {
     std::cerr << "Failed to open or create the db config file: " << cfname << std::endl;
     std::exit(EXIT_FAILURE);
@@ -61,6 +61,18 @@ VlogSet::VlogSet(std::string dbname, VlogGC *vlog_gc) : dbname(dbname), vlog_gc(
 }
 
 VlogSet::~VlogSet() {
+  // wait for all gc threads to finish
+  while (true) {
+    finished_latch_.lock();
+    if (!finished) {
+      finished_latch_.unlock();
+      std::this_thread::sleep_for(std::chrono::milliseconds(2));
+    } else {
+      finished_latch_.unlock();
+      break;
+    }
+  }
+
   config_file_->seekp(0);
   config_file_->write(reinterpret_cast<const char*>(&vlog_nums_), sizeof(size_t));
   config_file_->flush();
@@ -69,6 +81,7 @@ VlogSet::~VlogSet() {
   for (auto & it : vlog_info_map_) {
     struct vlog_info* vinfo = it.second;
 
+    // 所有操作都已经同步完成
     // 使用 vlog_info* 进行操作
     size_t tmp[2] = {vinfo->curr_size, vinfo->value_nums};
     auto vlog_file_handler = std::fstream(get_vlog_name(vinfo->vlog_num), std::ios::in | std::ios::out);
@@ -82,20 +95,22 @@ VlogSet::~VlogSet() {
 
 }
 
-void VlogSet::get_value(uint32_t vlog_num, uint32_t value_offset, std::string *value) {
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+void VlogSet::get_value(const struct slot_content &sc, std::string *value) {
   mtx.lock();
-  auto vinfo = get_vlog_info(vlog_num);
-  auto vhandler = get_vlog_handler(vlog_num);
+  auto vinfo = get_vlog_info(sc.vlog_num);
+  auto vhandler = get_vlog_handler(sc.vlog_num);
 
   vinfo->vlog_info_latch_.lock();
   if (!vinfo->vlog_valid_) {
     vhandler = get_vlog_handler(vinfo->vlog_num_for_gc);
   }
   vhandler->vlog_latch_.soft_lock();
+  mtx.unlock(); // for better performance
   vinfo->vlog_info_latch_.unlock();
-  read_vlog_value(vlog_num, value_offset, value);
+  read_vlog_value(sc, value);
   vhandler->vlog_latch_.soft_unlock();
-  mtx.unlock();
 }
 
 struct vlog_info * VlogSet::get_writable_vlog_info(size_t value_size) {
@@ -103,16 +118,21 @@ struct vlog_info * VlogSet::get_writable_vlog_info(size_t value_size) {
     struct vlog_info* vinfo = it->second;
 
     // 使用 vlog_info* 进行操作
-    if (vinfo->curr_size + value_size <= VLOG_SIZE) {
+    vinfo->vlog_info_latch_.lock();
+    if (vinfo->vlog_valid_ && !vinfo->processing_gc && vinfo->curr_size+value_size <= VLOG_SIZE) {
+      vinfo->vlog_info_latch_.unlock();
       return vinfo;
     }
+    vinfo->vlog_info_latch_.unlock();
   }
 
   // 所有vlog已满，创建新vlog
   return nullptr;
 }
 
-void VlogSet::put_value(uint32_t *vlog_num, uint32_t *value_offset, const leveldb::Slice &value) {
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+void VlogSet::put_value(struct slot_content &sc, size_t slot_num, const leveldb::Slice &value) {
   mtx.lock();
 
   auto vinfo = get_writable_vlog_info(value.size());
@@ -123,82 +143,69 @@ void VlogSet::put_value(uint32_t *vlog_num, uint32_t *value_offset, const leveld
   }
 
   vinfo->vlog_info_latch_.lock();
-  *vlog_num = vinfo->vlog_num;
-  *value_offset = vinfo->curr_size;
-  vinfo->curr_size += value.size();
+  sc.vlog_num = vinfo->vlog_num;
+  sc.value_offset = vinfo->curr_size;
+  vinfo->curr_size += value.size() + sizeof(uint16_t) + sizeof(size_t);
   vinfo->value_nums ++;
-  vinfo->vlog_info_latch_.unlock();
-
-  auto vhandler = get_vlog_handler(*vlog_num);
 
-  vinfo->vlog_info_latch_.lock();
-  if (!vinfo->vlog_valid_) {
+  auto vhandler = get_vlog_handler(vinfo->vlog_num);
+  if (!vinfo->vlog_valid_ || vinfo->processing_gc) {
     vhandler = get_vlog_handler(vinfo->vlog_num_for_gc);
   }
+
   vhandler->vlog_latch_.hard_lock();
+  mtx.unlock(); // for better performance
   vinfo->vlog_info_latch_.unlock();
-  write_vlog_value(*vlog_num, *value_offset, value);
+  write_vlog_value(sc, slot_num, value);
   vhandler->vlog_latch_.hard_unlock();
-  mtx.unlock();
 }
 
-void VlogSet::del_value(uint32_t vlog_num, uint32_t value_offset) {
+void VlogSet::del_value(const struct slot_content &sc) {
   mtx.lock();
-  auto vinfo = get_vlog_info(vlog_num);
-  auto vhandler = get_vlog_handler(vlog_num);
+  auto vinfo = get_vlog_info(sc.vlog_num);
+  auto vhandler = get_vlog_handler(sc.vlog_num);
 
   vinfo->vlog_info_latch_.lock();
-  if (!vinfo->vlog_valid_) {
-//    auto vlog_num_gc = vinfo->vlog_num_for_gc;
+  if (!vinfo->vlog_valid_ || vinfo->processing_gc) {
     vhandler = get_vlog_handler(vinfo->vlog_num_for_gc);
-//    vinfo->vlog_info_latch_.unlock();
-//    vinfo = get_vlog_info(vlog_num_gc);
-//    vinfo->vlog_info_latch_.lock();
   }
-  vhandler->vlog_latch_.hard_lock();
-  mark_del_value(vlog_num, value_offset);
 
+  vhandler->vlog_latch_.hard_lock();
+  mtx.unlock();  // for better performance
   vinfo->vlog_info_latch_.unlock();
+  mark_del_value(sc);
   vhandler->vlog_latch_.hard_unlock();
-  mtx.unlock();
 }
 
 size_t VlogSet::register_new_vlog() {
+  // FIXME: concurrency on config file
   size_t vn = vlog_nums_;
   std::string vlog_name = get_vlog_name(vn);
   register_inconfig_file(vn);
   create_vlog(vn);
-//  auto vlog_new = new std::fstream(vlog_name, std::ios::in | std::ios::out);
-//  if (!vlog_new->is_open()) {
-//    std::cerr << "Failed to open or create the vlog file: " << vlog_new << std::endl;
-//    std::exit(EXIT_FAILURE);
-//  }
   register_vlog_inmaps(vn, vlog_name);
   vlog_nums_ ++;
-//  vlog_count_ ++;
   return vn;
 }
 
+// only used in vlog gc
 void VlogSet::remove_old_vlog(size_t old_vlog_num) {
   // after gc, new_vlog has been created
-  // new vlog should have been created here !
+  // new vlog should have been created here
   mtx.lock();
   auto vi_old = get_vlog_info(old_vlog_num);
   vi_old->vlog_info_latch_.lock();
   std::string old_vlog_name = get_vlog_name(old_vlog_num);
   remove_from_config_file(old_vlog_num);
-  remove_vlog_from_maps(old_vlog_name);
+//  remove_vlog_from_maps(old_vlog_name); // FIXME: this function should be called after all access on this vlog finished !!!
   vi_old->vlog_valid_ = false;
   vi_old->vlog_info_latch_.unlock();
-//  vlog_count_ --;
   mtx.unlock();
 }
 
 bool VlogSet::vlog_need_gc(size_t vlog_num) {
-  // FIXME: vlog应该已经满了才行
-  std::string vlog_name = get_vlog_name(vlog_num);
-  auto vi = vlog_info_map_[vlog_name];
-  if ((double)vi->curr_size/VLOG_SIZE < VLOG_GC_THREHOLD) {
+  auto vi = get_vlog_info(vlog_num);
+  if ((double)(vi->curr_size*1.0)/VLOG_SIZE < VLOG_GC_THREHOLD) {
     return false;
   }
   bool retval = vi->vlog_valid_ && (vi->discard/vi->value_nums >= GC_THREDHOLD);
@@ -209,12 +216,16 @@ void VlogSet::register_inconfig_file(size_t vlog_num) {
   // config file: | vlog_nums_(size_t) | vlog_count_(size_t) | vlog_1_name | ... |
   // first size_t in config file indicates current vlog_nums_(size_t)
   // second size_t in config file indicates current vlog_count_(size_t)
+  config_file_latch_.lock();
   config_file_->seekp(sizeof(size_t) + vlog_nums_* sizeof(size_t));
   config_file_->write(reinterpret_cast<const char*>(&vlog_num), sizeof(size_t));
   config_file_->flush();
+  config_file_latch_.unlock();
 }
 
 void VlogSet::remove_from_config_file(size_t vlog_num) {
+  // FIXME: concurrency on config file
+  config_file_latch_.lock();
   char tmp[vlog_nums_*vlog_num_size];
   config_file_->seekp(sizeof(size_t));
   config_file_->read(tmp, sizeof(tmp));
@@ -229,6 +240,7 @@ void VlogSet::remove_from_config_file(size_t vlog_num) {
       break;
     }
   }
+  config_file_latch_.unlock();
 }
 
 void VlogSet::create_vlog(size_t vlog_num) {
@@ -264,14 +276,8 @@ inline void VlogSet::register_vlog_inmaps(size_t vlog_num, std::string &vlog_nam
 }
 
 inline void VlogSet::remove_vlog_from_maps(std::string &vlog_name) {
-  auto vi = vlog_info_map_[vlog_name];
-  //    auto vh = vlog_handler_map_[vlog_name];
-  vi->vlog_info_latch_.lock();
-  vi->vlog_valid_ = false; // TODO: change the slotpage vlog_num when get/put thread read this flag
-                            //    vh->handler_->close();
   assert(!std::remove(vlog_name.c_str()));
   vlog_handler_map_.erase(vlog_name);
-  vi->vlog_info_latch_.unlock();
 }
 
 inline std::string VlogSet::get_config_file_name() {
@@ -290,42 +296,57 @@ struct vlog_handler * VlogSet::get_vlog_handler(size_t vlog_num) {
   return vlog_handler_map_[get_vlog_name(vlog_num)];
 }
 
-// value: | value_size(uint16_t) | slot_num(size_t) | field_nums(uint16_t) ｜ value |
-void VlogSet::read_vlog_value(uint32_t vlog_num, uint32_t value_offset, std::string *value) {
-  auto vlog_name = get_vlog_name(vlog_num);
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+void VlogSet::read_vlog_value(const struct slot_content &sc, std::string *value) {
+  auto vlog_name = get_vlog_name(sc.vlog_num);
   auto handler = std::fstream(vlog_name, std::ios::in | std::ios::out);
-  handler.seekp(value_offset);
+  handler.seekp(sc.value_offset);
   char value_buff[VALUE_BUFF_SIZE];
   handler.read(value_buff, VALUE_BUFF_SIZE);
 
-  // FIXME: remove value size
   uint16_t value_size;
   memcpy(&value_size, value_buff, sizeof(uint16_t));
+  if (value_size & VALUE_DELE_MASK) {
+    *value = "";
+    return ;
+  }
   value_size &= VALUE_SIZE_MASK;
-//  *value = std::string(value_buff);
   assert(value_size <= VALUE_BUFF_SIZE);
-  value->assign(&value_buff[sizeof(uint16_t)], value_size);
+
+  const size_t off = sizeof(uint16_t)+sizeof(size_t);
+  *value = std::string(&value_buff[off], value_size-off);
   handler.close();
 }
 
-void VlogSet::write_vlog_value(uint32_t vlog_num, uint32_t value_offset, const leveldb::Slice &value) {
-  auto vlog_name = get_vlog_name(vlog_num);
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+void VlogSet::write_vlog_value(const struct slot_content &sc, size_t slot_num, const leveldb::Slice &value) {
+  auto vlog_name = get_vlog_name(sc.vlog_num);
   auto handler = std::fstream(vlog_name, std::ios::in | std::ios::out);
-  handler.seekp(value_offset);
+  handler.seekp(sc.value_offset);
   const char *value_buff = value.data();
-  handler.write(value_buff, value.size());
 
-  auto vinfo = get_vlog_info(vlog_num);
+  const size_t off = sizeof(uint16_t) + sizeof(size_t);
+  const size_t value_size = off + value.size();
+  char data[value_size];
+  memcpy(data, &value_size, sizeof(uint16_t));
+  memcpy(data+sizeof(uint16_t), &slot_num, sizeof(size_t));
+  memcpy(data+off, value_buff, value.size());
+
+  handler.write(data, value_size);
 
   handler.flush();
   handler.close();
 }
 
-void VlogSet::mark_del_value(uint32_t vlog_num, uint32_t value_offset) {
-  auto vinfo = get_vlog_info(vlog_num);
-  auto vlog_name = get_vlog_name(vlog_num);
+// single value: || value_size(uint16_t) | slot_num(size_t) || {field_nums(uint16_t), attr1, attr2, ... } |
+// single attr: | attr1_name_len(uint8_t) | attr1_name | attr1_len(uint16_t) | attr1 |
+void VlogSet::mark_del_value(const struct slot_content &sc) {
+  auto vinfo = get_vlog_info(sc.vlog_num);
+  auto vlog_name = get_vlog_name(sc.vlog_num);
   auto handler = std::fstream(vlog_name, std::ios::in | std::ios::out);
-  handler.seekp(value_offset);
+  handler.seekp(sc.value_offset);
   char value_buff[VALUE_BUFF_SIZE];
   handler.read(value_buff, VALUE_BUFF_SIZE);
 
@@ -337,22 +358,22 @@ void VlogSet::mark_del_value(uint32_t vlog_num, uint32_t value_offset) {
     return ;
   }
   assert(!(value_size & VALUE_DELE_MASK));
-  uint16_t masked_value_size = value_size | VALUE_DELE_MASK;
+  uint16_t masked_value_size = value_size | (uint16_t)VALUE_DELE_MASK;
   memcpy(value_buff, &masked_value_size, sizeof(uint16_t));
-  handler.write(value_buff, value_size);
+  handler.seekp(sc.value_offset);
+  handler.write(value_buff, sizeof(uint16_t));
   handler.flush();
   handler.close();
 
   // handle gc, mtx is locked outside, vlog_info_latch and vlog hard lock is locked outside too
-  //    auto vinfo = get_vlog_info(vlog_num);
   vinfo->discard ++;
   vinfo->value_nums --;
-  vinfo->curr_size -= value_size & VALUE_SIZE_MASK;
-  if (vlog_need_gc(vlog_num)) {
+  vinfo->curr_size -= value_size;
+  // FIXME: gc process
+  if (vlog_need_gc(sc.vlog_num) && !vinfo->processing_gc) {
     // create new vlog
-    vinfo->vlog_valid_ = false;
+    vinfo->processing_gc = true;
     vinfo->vlog_num_for_gc = register_new_vlog();
-    //      vinfo->vlog_valid_ = false;
-    vlog_gc->do_gc(vlog_num, vinfo->vlog_num_for_gc);
+    vlog_gc->do_gc(sc.vlog_num, vinfo->vlog_num_for_gc);
   }
 }
diff --git a/db/vlog_set.h b/db/vlog_set.h
index a4f031c..dd44725 100644
--- a/db/vlog_set.h
+++ b/db/vlog_set.h
@@ -9,6 +9,7 @@
 #include <string>
 #include <mutex>
 #include <cassert>
+#include <condition_variable>
 #include "../include/leveldb/slice.h"
 #include "../db/shared_lock.h"
 #include "../db/vlog.h"
@@ -18,6 +19,7 @@ class VlogGC;
 
 class VlogSet {
 friend class VlogGC;
+friend class gc_executor;
 
 #define CONFIG_FILE_DELE_MASK       (0x1 << (sizeof(size_t)-1))
 #define CONFIG_FILE_VLOG_NUM(v)     ((v) & ~CONFIG_FILE_DELE_MASK)
@@ -25,9 +27,9 @@ friend class VlogGC;
  public:
   VlogSet(std::string dbname, VlogGC *vlog_gc);
   ~VlogSet();
-  void get_value(uint32_t vlog_num, uint32_t value_offset, std::string *value);
-  void put_value(uint32_t *vlog_num, uint32_t *value_offset, const leveldb::Slice &value);
-  void del_value(uint32_t vlog_num, uint32_t value_offset);
+  void get_value(const struct slot_content &sc, std::string *value);
+  void put_value(struct slot_content &sc, size_t slot_num, const leveldb::Slice &value);
+  void del_value(const struct slot_content &sc);
 
   void set_vlog_gc(VlogGC *vg) { this->vlog_gc = vg; }
 
@@ -47,19 +49,24 @@ friend class VlogGC;
   std::string get_vlog_name(size_t vlog_num);
   struct vlog_info *get_vlog_info(size_t vlog_num);
   struct vlog_handler *get_vlog_handler(size_t vlog_num);
-  void read_vlog_value(uint32_t vlog_num, uint32_t value_offset, std::string *value);
-  void write_vlog_value(uint32_t vlog_num, uint32_t value_offset, const leveldb::Slice &value);
-  void mark_del_value(uint32_t vlog_num, uint32_t value_offset);
+  void read_vlog_value(const struct slot_content &sc, std::string *value);
+  void write_vlog_value(const struct slot_content &sc, size_t slot_num, const leveldb::Slice &value);
+  void mark_del_value(const struct slot_content &sc);
 
  private:
   std::mutex mtx;
   std::string dbname;
   size_t vlog_nums_;
-//  size_t vlog_count_;
   std::unordered_map<std::string, struct vlog_info *> vlog_info_map_;
   std::unordered_map<std::string, struct vlog_handler *> vlog_handler_map_;
+  std::mutex config_file_latch_;
   std::fstream *config_file_;
 
+  int counter = 0;
+  std::mutex counter_latch_;
+  std::mutex finished_latch_;
+  bool finished = false;
+
   VlogGC *vlog_gc;  // 仅声明为指针，具体定义放在 vlog_set.cpp
 };
 
diff --git a/include/leveldb/db.h b/include/leveldb/db.h
index 82493de..6d739b4 100644
--- a/include/leveldb/db.h
+++ b/include/leveldb/db.h
@@ -156,7 +156,7 @@ class LEVELDB_EXPORT DB {
   // 字段信息结构体
   // Todo(begin)
   virtual Status Put_Fields(const leveldb::WriteOptions& opt, const leveldb::Slice& key, const FieldArray& fields) = 0;
-  virtual Status Get_Fields(const leveldb::ReadOptions& options, const leveldb::Slice& key, FieldArray* fields) = 0;
+  virtual Status Get_Fields(const leveldb::ReadOptions& options, const leveldb::Slice& key, FieldArray& fields) = 0;
   //  // Todo(end)
 };
 
diff --git a/test/db_test1.cc b/test/db_test1.cc
index ade9372..7ce6779 100644
--- a/test/db_test1.cc
+++ b/test/db_test1.cc
@@ -4,11 +4,11 @@
 using namespace std;
 using namespace leveldb;
 
-int main() {
+int test1() {
   DB* db = nullptr;
   Options op;
   op.create_if_missing = true;
-  Status status = DB::Open(op, "testdb", &db);
+  Status status = DB::Open(op, "testdb1", &db);
   assert(status.ok());
   db->Put(WriteOptions(), "001", "leveldb");
   string s;
@@ -18,11 +18,53 @@ int main() {
 
   db->Put(WriteOptions(), "002", "world");
   string s1;
-  db->Delete(WriteOptions(), "002");
+  db->Delete(WriteOptions(), "002"); // sc: {0, 33}
   db->Get(ReadOptions(), "002", &s1);
   cout << s1.size() << endl;
   cout<<s1<<endl;
 
   delete db;
   return 0;
+}
+
+
+int test2() {
+  DB* db = nullptr;
+  Options op;
+  op.create_if_missing = true;
+  Status status = DB::Open(op, "testdb2", &db);
+  assert(status.ok());
+
+  const std::string value_prefix = "value_";
+  const size_t loop_times = 1000;
+  for (auto i = 0; i < loop_times; i++) {
+    auto key = std::to_string(i);
+    auto value = value_prefix + key;
+    db->Put(WriteOptions(), key, value);
+    string s;
+    db->Get(ReadOptions(), key, &s);
+    cout << s << " | " << s.size() << endl;
+
+  }
+
+  cout << endl << "all put are done" << endl << endl;
+
+  for (auto i = 0; i < loop_times; i++) {
+    auto key = std::to_string(i);
+    auto value = value_prefix + key;
+
+//    db->Put(WriteOptions(), key, value+"_");
+    string s1;
+    db->Delete(WriteOptions(), key);  // sc: {0, 33}
+    db->Get(ReadOptions(), key, &s1);
+    cout << s1 << " | " << s1.size() << " | " << i << endl;
+  }
+
+  delete db;
+  return 0;
+}
+
+
+int main() {
+  test2();
 }
\ No newline at end of file