diff --git a/db/builder.cc b/db/builder.cc
index 7cf13f8..780e6f9 100644
--- a/db/builder.cc
+++ b/db/builder.cc
@@ -28,6 +28,7 @@ Status BuildTable(const std::string& dbname, Env* env, const Options& options,
       return s;
     }
 
+    // 如果第一个字节是 0x01，它会移除这个前缀，并尝试从剩下的数据中解析出 value
     {
       auto tmp_value=iter->value();
       if(tmp_value.data()[0]==(char)(0x01)){
diff --git a/db/db_impl.cc b/db/db_impl.cc
index 56d51ec..82d9ce7 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -839,8 +839,8 @@ Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
     compact->builder = new TableBuilder(options_, compact->outfile);
   }
 
-  
-  compact->valuelog_offset=0;
+  // compaction 后的新 valuelog
+  compact->valuelog_offset=0; // why
   s = env_->NewWritableFile(ValueLogFileName(dbname_,compact->valuelog_file_id), &compact->valuelogfile);
   
   return s;
@@ -878,6 +878,7 @@ Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
   }
   delete compact->outfile;
   compact->outfile = nullptr;
+  // value log 落盘
   if (s.ok()) {
     s = compact->valuelogfile->Flush();
   }
@@ -955,9 +956,13 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   std::string current_user_key;
   bool has_current_user_key = false;
   SequenceNumber last_sequence_for_key = kMaxSequenceNumber;
+  // 记录 当前和下一层 level 中被合并的 files
   for (int which = 0; which < 2; which++) {
     for (int i = 0; i < compact->compaction->num_input_files(which); i++) {
-      if(compact->compaction->input(which, i)->valuelog_id)oldvaluelog_ids[compact->compaction->input(which, i)->number]=compact->compaction->input(which, i)->valuelog_id;
+      auto tmp_file=compact->compaction->input(which, i);
+      if(tmp_file->valuelog_id){
+        oldvaluelog_ids[tmp_file->number]=tmp_file->valuelog_id;
+      }
     }
   }
   while (input->Valid() && !shutting_down_.load(std::memory_order_acquire)) {
@@ -1044,31 +1049,39 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
       Slice old_value=input->value();
       Slice new_value;
       std::string buf="";
-      if(old_value.size()==0||old_value.data()[0]==(char)(0x00)){//when it is a deletion, input->value() will be ""
+      if(old_value.size()==0||old_value.data()[0]==(char)(0x00)){
+        // when it is a deletion, input->value() will be ""
         new_value=old_value;
       }
       else{
+        // not delete
         old_value.remove_prefix(1);
-        uint64_t file_id,valuelog_offset,valuelog_len;
+        // put value_len into value_log
+        int value_offset=sizeof(uint64_t)*2;// 16
+        // uint64_t file_id,valuelog_offset,valuelog_len;
+        uint64_t file_id,valuelog_offset;
         bool res=GetVarint64(&old_value,&file_id);
         if(!res)assert(0);
         res=GetVarint64(&old_value,&valuelog_offset);
         if(!res)assert(0);
-        res=GetVarint64(&old_value,&valuelog_len);
-        if(!res)assert(0);
-        Status s=ReadValueLog(file_id,valuelog_offset,valuelog_len,&new_value);
+        // res=GetVarint64(&old_value,&valuelog_len);
+        // if(!res)assert(0);
+        // Status s=ReadValueLog(file_id,valuelog_offset,valuelog_len,&new_value);
+        Status s=ReadValueLog(file_id,valuelog_offset,&new_value);
         assert(s.ok());
         writeValueLogForCompaction(compact->valuelogfile,{new_value});
         buf+=(char)(0x01);
         PutVarint64(&buf,compact->valuelog_file_id);
         PutVarint64(&buf,compact->valuelog_offset);
-        PutVarint64(&buf,valuelog_len);
-        compact->valuelog_offset+=valuelog_len;
+        // PutVarint64(&buf,valuelog_len);
+        compact->valuelog_offset+=value_offset;
         delete []new_value.data();
         new_value=Slice(buf);
       }
       
       compact->builder->Add(key, new_value);
+      // 更新计数器
+      // compact->builder->add_log_count();
 
       // Close output file if it is big enough
       if (compact->builder->FileSize() >=
@@ -1241,14 +1254,18 @@ Status DBImpl::Get(const ReadOptions& options, const Slice& key,
   }
   Slice value_log_slice=Slice(value->c_str()+1,value->length());
   Slice new_value;
-  uint64_t file_id,valuelog_offset,valuelog_len;
+  // put value_len into value_log
+  int value_offset=sizeof(uint64_t)*2;// 16
+  // uint64_t file_id,valuelog_offset,valuelog_len;
+  uint64_t file_id,valuelog_offset;
   bool res=GetVarint64(&value_log_slice,&file_id);
   if(!res)return Status::Corruption("can't decode file id");
   res=GetVarint64(&value_log_slice,&valuelog_offset);
   if(!res)return Status::Corruption("can't decode valuelog offset");
-  res=GetVarint64(&value_log_slice,&valuelog_len);
-  if(!res)return Status::Corruption("can't decode valuelog len");
-  ReadValueLog(file_id,valuelog_offset,valuelog_len,&new_value);
+  // res=GetVarint64(&value_log_slice,&valuelog_len);
+  // if(!res)return Status::Corruption("can't decode valuelog len");
+  // ReadValueLog(file_id,valuelog_offset,valuelog_len,&new_value);
+  ReadValueLog(file_id,valuelog_offset,&new_value);
   *value=std::string(new_value.data(),new_value.size());
   delete []new_value.data();
   return s;
@@ -1574,35 +1591,66 @@ void DBImpl::GetApproximateSizes(const Range* range, int n, uint64_t* sizes) {
 
   v->Unref();
 }
-std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> DBImpl::WriteValueLog(std::vector<Slice> values){
-  //lock
-  // std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> res;
-  // for(int i=0;i<values.size();i++){
-  //   int len=values[i].size();
-  //   valuelogfile_->Append(values[i]);
-  //   res.push_back({valuelogfile_number_,{valuelogfile_offset,len}});
-  //   valuelogfile_offset+=len;
-  // }
-  // //unlock
-  // valuelogfile_->Flush();
-  // return res;
-  std::string file_name_=ValueLogFileName(dbname_,valuelogfile_number_);
+// std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> DBImpl::WriteValueLog(std::vector<Slice> values){
+
+//   std::string file_name_=ValueLogFileName(dbname_,valuelogfile_number_);
+//   std::ofstream valueFile(file_name_, std::ios::app | std::ios::binary);
+//   if (!valueFile.is_open()) {
+//         assert(0);
+//     }
+//   uint64_t offset=valueFile.tellp();
+//   std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> res;
+//   for(int i=0;i<values.size();i++){
+//     int len=values[i].size();
+//     valueFile.write(values[i].data(),len);
+//     res.push_back({valuelogfile_number_,{offset,len}});
+//     offset+=len;
+//   }
+//   //unlock
+//   valueFile.close();
+//   return res;
+// }
+
+std::vector<std::pair<uint64_t, uint64_t>> DBImpl::WriteValueLog(std::vector<Slice> values) {
+  std::string file_name_ = ValueLogFileName(dbname_, valuelogfile_number_);
   std::ofstream valueFile(file_name_, std::ios::app | std::ios::binary);
   if (!valueFile.is_open()) {
-        assert(0);
+      assert(0);
+  }
+
+  uint64_t offset = valueFile.tellp();
+  std::vector<std::pair<uint64_t, uint64_t>> res;
+
+  for (const auto& slice : values) {
+    uint64_t len = slice.size();
+
+    // 先写入长度
+    valueFile.write(reinterpret_cast<const char*>(&len), sizeof(uint64_t));
+    if (!valueFile.good()) {
+        valueFile.close();
+        return {}; // 写入长度失败，返回空结果
     }
-  uint64_t offset=valueFile.tellp();
-  std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> res;
-  for(int i=0;i<values.size();i++){
-    int len=values[i].size();
-    valueFile.write(values[i].data(),len);
-    res.push_back({valuelogfile_number_,{offset,len}});
-    offset+=len;
+
+    // 再写入实际数据
+    valueFile.write(slice.data(), len);
+    if (!valueFile.good()) {
+        valueFile.close();
+        return {}; // 写入数据失败，返回空结果
+    }
+
+    // 记录 file_id 和 offset
+    res.push_back({valuelogfile_number_, offset});
+
+    // 更新偏移量，包括长度信息
+    offset += sizeof(uint64_t) + len;
   }
-  //unlock
+
+  // 解锁资源或进行其他清理操作
+
   valueFile.close();
   return res;
 }
+
 void DBImpl::writeValueLogForCompaction(WritableFile* target_file,std::vector<Slice> values){
   for(int i=0;i<values.size();i++){
     target_file->Append(values[i]);
@@ -1610,34 +1658,73 @@ void DBImpl::writeValueLogForCompaction(WritableFile* target_file,std::vector<Sl
 }
 
 void DBImpl::addNewValueLog(){
-  //lock
-  // if(valuelogfile_){
-  //   valuelogfile_->Sync();
-  //   valuelogfile_->Close();
-  //   delete valuelogfile_;
-  // }
   valuelogfile_number_=versions_->NewFileNumber();
-  // valuelogfile_offset=0;
-  // std::string file_name_=ValueLogFileName(dbname_,valuelogfile_number_);
-  // env_->NewWritableFile(file_name_,&valuelogfile_);
-  //unlock
 }
 
-Status DBImpl::ReadValueLog(uint64_t file_id, uint64_t offset,uint64_t len,Slice* value){
+// Status DBImpl::ReadValueLog(uint64_t file_id, uint64_t offset,uint64_t len,Slice* value){
+//   //lock_shared
+//   Status s=Status::OK();
+//   std::string file_name_=ValueLogFileName(dbname_,file_id);
+//   //std::cout<<file_name_<<" "<<offset<<" "<<len<<std::endl;
+//   std::ifstream inFile(file_name_, std::ios::in | std::ios::binary);
+//   if (!inFile.is_open()) {
+//       std::cerr << "Failed to open file for writing!"<<file_id<<" "<<offset<<" "<<len<< std::endl;
+//       return Status::Corruption("Failed to open file for writing!");
+//   }
+//   inFile.seekg(offset);
+//   char *value_buf=new char[len];
+//   inFile.read(value_buf,len);
+//   // check available
+//   // s=check_value_available(value_buf);
+//   inFile.close();
+//   *value=Slice(value_buf,len);
+//   return s;
+// }
+
+Status DBImpl::ReadValueLog(uint64_t file_id, uint64_t offset, Slice* value) {
   //lock_shared
-  std::string file_name_=ValueLogFileName(dbname_,file_id);
-  //std::cout<<file_name_<<" "<<offset<<" "<<len<<std::endl;
+  Status s = Status::OK();
+  std::string file_name_ = ValueLogFileName(dbname_, file_id);
+  
+  // Open the file in binary mode for reading
   std::ifstream inFile(file_name_, std::ios::in | std::ios::binary);
   if (!inFile.is_open()) {
-      std::cerr << "Failed to open file for writing!"<<file_id<<" "<<offset<<" "<<len<< std::endl;
-      return Status::Corruption("Failed to open file for writing!");
+      std::cerr << "Failed to open file: " << file_name_ << " for reading!" << std::endl;
+      return Status::Corruption("Failed to open file for reading!");
   }
+
+  // Seek to the position of len
   inFile.seekg(offset);
-  char *value_buf=new char[len];
-  inFile.read(value_buf,len);
+
+  // Read the length of the value
+  uint64_t len;
+  inFile.read(reinterpret_cast<char*>(&len), sizeof(uint64_t));
+  if (!inFile.good()) {
+      inFile.close();
+      return Status::Corruption("Failed to read length from file!");
+  }
+
+  // Now seek to the actual data position and read the value
+  inFile.seekg(offset + sizeof(uint64_t));
+  char* value_buf = new char[len];
+  inFile.read(value_buf, len);
+  if (!inFile.good()) {
+      delete[] value_buf;
+      inFile.close();
+      return Status::Corruption("Failed to read value from file!");
+  }
+
+  // Close the file after reading
   inFile.close();
-  *value=Slice(value_buf,len);
-  return Status::OK();
+
+  // Assign the read data to the Slice
+  *value = Slice(value_buf, len);
+
+  // Clean up allocated buffer
+  // should also do in v2
+  delete[] value_buf;
+
+  return s;
 }
 
 // Default implementations of convenience methods that subclasses of DB
diff --git a/db/db_impl.h b/db/db_impl.h
index ab21773..513690b 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -63,11 +63,14 @@ class DBImpl : public DB {
   bool GetProperty(const Slice& property, std::string* value) override;
   void GetApproximateSizes(const Range* range, int n, uint64_t* sizes) override;
   void CompactRange(const Slice* begin, const Slice* end) override;
-  std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> WriteValueLog(std::vector<Slice> value)override;
+  // std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> WriteValueLog(std::vector<Slice> value)override;
+  std::vector<std::pair<uint64_t,uint64_t>> WriteValueLog(std::vector<Slice> value)override;
   void writeValueLogForCompaction(WritableFile* target_file,std::vector<Slice> value);
   void addNewValueLog()override EXCLUSIVE_LOCKS_REQUIRED(mutex_);;
   std::pair<WritableFile*,uint64_t> getNewValuelog();//use for compaction
-  Status ReadValueLog(uint64_t file_id, uint64_t offset,uint64_t len,Slice* value)override;
+  // Status ReadValueLog(uint64_t file_id, uint64_t offset,uint64_t len,Slice* value)override;
+  Status ReadValueLog(uint64_t file_id, uint64_t offset,Slice* value)override;
+
 
   // Extra methods (for testing) that are not in the public DB interface
 
diff --git a/db/db_iter.cc b/db/db_iter.cc
index 28d227e..350d175 100644
--- a/db/db_iter.cc
+++ b/db/db_iter.cc
@@ -79,9 +79,10 @@ class DBIter : public Iterator {
     if(!res)assert(0);
     res=GetVarint64(&tmp_value,&valuelog_offset);
     if(!res)assert(0);
-    res=GetVarint64(&tmp_value,&valuelog_len);
-    if(!res)assert(0);
-    db_->ReadValueLog(file_id,valuelog_offset,valuelog_len,&tmp_value);
+    // res=GetVarint64(&tmp_value,&valuelog_len);
+    // if(!res)assert(0);
+    // db_->ReadValueLog(file_id,valuelog_offset,valuelog_len,&tmp_value);
+    db_->ReadValueLog(file_id,valuelog_offset,&tmp_value);
     return tmp_value;
   }
   Status status() const override {
diff --git a/db/write_batch.cc b/db/write_batch.cc
index 77af25a..14df572 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -149,8 +149,9 @@ class ValueLogInserter : public WriteBatch::Handler {
       v.push_back(value);
       auto res=db_->WriteValueLog(v);
       PutVarint64(&buf,res[0].first);
-      PutVarint64(&buf,res[0].second.first);
-      PutVarint64(&buf,res[0].second.second);
+      // PutVarint64(&buf,res[0].second.first);
+      // PutVarint64(&buf,res[0].second.second);
+      PutVarint64(&buf,res[0].second);
     }
     new_value=Slice(buf);
     writeBatch_.Put(key,new_value);  
diff --git a/include/leveldb/db.h b/include/leveldb/db.h
index 566fbee..116744f 100644
--- a/include/leveldb/db.h
+++ b/include/leveldb/db.h
@@ -102,19 +102,29 @@ class LEVELDB_EXPORT DB {
   
   // virtual Status Get_keys_by_field(const ReadOptions& options, const Field field,std::vector<std::string> *keys);
 
-  virtual std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> WriteValueLog(std::vector<Slice> value){
+  // virtual std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> WriteValueLog(std::vector<Slice> value){
+  //   assert(0);
+  //   std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> v;
+  //   return v;
+  // }
+  virtual std::vector<std::pair<uint64_t,uint64_t>> WriteValueLog(std::vector<Slice> value){
     assert(0);
-    std::vector<std::pair<uint64_t,std::pair<uint64_t,uint64_t>>> v;
+    std::vector<std::pair<uint64_t,uint64_t>> v;
     return v;
   }
 
   virtual void addNewValueLog(){assert(0);}
 
-  virtual Status ReadValueLog(uint64_t file_id, uint64_t offset,uint64_t len,Slice* value){
+  // virtual Status ReadValueLog(uint64_t file_id, uint64_t offset,uint64_t len,Slice* value){
+  //   assert(0);  // Not implemented
+  //   return Status::Corruption("not imp");
+  // }
+  virtual Status ReadValueLog(uint64_t file_id, uint64_t offset,Slice* value){
     assert(0);  // Not implemented
     return Status::Corruption("not imp");
   }
 
+
   // Return a heap-allocated iterator over the contents of the database.
   // The result of NewIterator() is initially invalid (caller must
   // call one of the Seek methods on the iterator before using it).