diff --git a/db/db_impl.cc b/db/db_impl.cc
index ab747ba..1f4ec83 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -1263,19 +1263,17 @@ Iterator* DBImpl::NewIterator(const ReadOptions& options) {
   SequenceNumber latest_snapshot;
   uint32_t seed;
   int iter_num=24;
-  std::vector<Iterator*> iters(iter_num, nullptr);
-  for(int i=0;i<iter_num;i++){
-    Iterator* iter = NewInternalIterator(options, &latest_snapshot, &seed);
-    auto db_iter=NewDBIterator(this, user_comparator(), iter,
-                        (options.snapshot != nullptr
-                              ? static_cast<const SnapshotImpl*>(options.snapshot)
-                                    ->sequence_number()
-                              : latest_snapshot),
-                        seed);
-    iters[i]=db_iter;
-  }
-
-  Iterator* iter = NewInternalIterator(options, &latest_snapshot, &seed);
+  Iterator* iter_prefetch = NewInternalIterator(options, &latest_snapshot, &seed);
+  auto db_iter_prefetch=NewDBIterator(this, user_comparator(), iter_prefetch,
+                      (options.snapshot != nullptr
+                            ? static_cast<const SnapshotImpl*>(options.snapshot)
+                                  ->sequence_number()
+                            : latest_snapshot),
+                      seed);
+
+  SequenceNumber useless_snapshot;
+
+  Iterator* iter = NewInternalIterator(options, &useless_snapshot, &seed);
   auto db_iter=NewDBIterator(this, user_comparator(), iter,
                       (options.snapshot != nullptr
                             ? static_cast<const SnapshotImpl*>(options.snapshot)
@@ -1284,7 +1282,7 @@ Iterator* DBImpl::NewIterator(const ReadOptions& options) {
                       seed);
   
   
-  return NewPreFetchIterator(this,db_iter,iters,iter_num);
+  return NewPreFetchIterator(this,db_iter,db_iter_prefetch,iter_num);
 }
 
 void DBImpl::RecordReadSample(Slice key) {
@@ -1705,6 +1703,7 @@ Status DBImpl::ReadValueLog(uint64_t file_id, uint64_t offset, Slice* key,
 
   // Now seek to the actual key position and read the key
   inFile.seekg(offset + sizeof(uint64_t));
+  if(key_len>10000)assert(0);
   char* key_buf = new char[key_len];
   inFile.read(key_buf, key_len);
   if (!inFile.good()) {
diff --git a/db/db_impl.h b/db/db_impl.h
index a997387..369efb1 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -230,6 +230,7 @@ class DBImpl : public DB {
   uint64_t valuelogfile_number_;
   log::Writer* log_;
   std::map<uint64_t, uint64_t> oldvaluelog_ids;
+  std::map<uint64_t,RandomAccessFile*> mem_valuelogs;
   uint32_t seed_ GUARDED_BY(mutex_);  // For sampling.
 
   // Queue of writers.
diff --git a/db/dbformat.h b/db/dbformat.h
index 97cd1bb..2466307 100644
--- a/db/dbformat.h
+++ b/db/dbformat.h
@@ -45,7 +45,9 @@ static const int kMaxMemCompactLevel = 2;
 static const int kReadBytesPeriod = 1048576;
 
 // maximum size of value_log file
-static const int value_log_size=4<<24;
+static const int value_log_size=64<<20;
+
+static const int mem_value_log_number=(2<<30)/(value_log_size);
 
 }  // namespace config
 
diff --git a/db/prefetch_iter.cc b/db/prefetch_iter.cc
index 6c868ab..5f237cf 100644
--- a/db/prefetch_iter.cc
+++ b/db/prefetch_iter.cc
@@ -4,6 +4,7 @@
 #include <iostream>
 #include <fstream>
 #include <thread>
+#include <queue>
 #include "db/prefetch_iter.h"
 
 #include "db/db_impl.h"
@@ -37,9 +38,9 @@ class DBPreFetchIter : public Iterator {
   //     just before all entries whose user key == this->key().
   enum IterPos {Left,Mid,Right};
 
-  DBPreFetchIter(DBImpl* db, Iterator* iter, std::vector<Iterator*> prefetch_iters,int prefetch_num)
+  DBPreFetchIter(DBImpl* db, Iterator* iter, Iterator* prefetch_iter,int prefetch_num)
       : 
-        db_(db),iter_(iter),prefetch_iters_(prefetch_iters),prefetch_num_(prefetch_num) {}
+        db_(db),iter_(iter),prefetch_iter_(prefetch_iter),prefetch_num_(prefetch_num) {}
 
   DBPreFetchIter(const DBPreFetchIter&) = delete;
   DBPreFetchIter& operator=(const DBPreFetchIter&) = delete;
@@ -48,10 +49,9 @@ class DBPreFetchIter : public Iterator {
     if(prefetch_thread.joinable()){
       stop_flag.store(true);
       prefetch_thread.join();
-      for(auto iter:prefetch_iters_){
-        delete iter;
-      }
+      delete prefetch_iter_;
     }
+    else delete prefetch_iter_;
     std::cout<<"fetch:"<<fetched_<<" unfetch:"<<unfetched_<<"\n";
     delete iter_; 
   }
@@ -60,13 +60,13 @@ class DBPreFetchIter : public Iterator {
     return iter_->key();
   }
   Slice value() const override {
-    if(cur_pos>0&&cur_pos<1000000&&prefetched_array[cur_pos].load()){
+    if(cur_pos>=0&&cur_pos<=1000000&&prefetched_array[cur_pos].load()){
       fetched_++;
       return prefetch_array[cur_pos];
     }
     else{
       unfetched_++;
-      return GetAndParseTrueValue(iter_);
+      return GetAndParseTrueValue(iter_->value());
     }
   }
   Status status() const override {
@@ -80,86 +80,153 @@ class DBPreFetchIter : public Iterator {
   void SeekToLast() override;
 
  private:
-   Slice GetAndParseTrueValue(Iterator* iter)const{
-    Slice tmp_value=iter->value();
+   Slice GetAndParseTrueValue(Slice tmp_value)const{
     Slice key;
-    if(tmp_value.size()==0)return tmp_value;
-    if(tmp_value.data()[0]==0x00){
+    if(tmp_value.size()==0){
+      return Slice();
+    }
+    if(tmp_value.data()[0]==(char)(0x00)){
       tmp_value.remove_prefix(1);
-      return tmp_value;
+      char* s=new char[tmp_value.size()];
+      memcpy(s,tmp_value.data(),tmp_value.size());
+      return Slice(s,tmp_value.size());
     }
     tmp_value.remove_prefix(1);
-    uint64_t file_id,valuelog_offset,valuelog_len;
+    uint64_t file_id,valuelog_offset;
     bool res=GetVarint64(&tmp_value,&file_id);
     if(!res)assert(0);
     res=GetVarint64(&tmp_value,&valuelog_offset);
     if(!res)assert(0);
-    db_->ReadValueLog(file_id,valuelog_offset, &key, &tmp_value);
+    
+    Status s=db_->ReadValueLog(file_id,valuelog_offset, &key, &tmp_value);
+    if(!s.ok()){
+      std::cout<<std::string(tmp_value.data(),tmp_value.size())<<std::endl;
+      assert(0);
+    }
     return tmp_value;
   }
 
+
   void PreFetchThreadForward(){
     std::thread prefetch_threads[prefetch_num_];
+    std::queue<std::pair<std::string,int>> q;
+    port::Mutex* lock=new port::Mutex();
+    port::CondVar* cv=new port::CondVar(lock);
+    bool local_stop_flag=false;
+    int remaining_task_cnt=0;
+    bool main_finish=false;
     for(int i=0;i<prefetch_num_;i++){
-      Iterator* prefetch_iter_=prefetch_iters_[i];
-      int skip_num=i;
-      prefetch_threads[i]=std::thread([this,prefetch_iter_,skip_num]() {
-        int pos=skip_num;
-        for(int j=0;j<skip_num;j++){
-          if(prefetch_iter_->Valid())prefetch_iter_->Next();
-        }
-        while(prefetch_iter_->Valid()){
-          Slice key_=prefetch_iter_->key();
-          std::string str_key=std::string(key_.data(),key_.size());
-          Slice val=GetAndParseTrueValue(prefetch_iter_);
-          prefetch_array[pos]=val;
-          prefetched_array[pos].store(true);
-          if(stop_flag.load()||pos>1000000){
-            break;
-          }
-          for(int j=0;j<prefetch_num_;j++){
-            if(prefetch_iter_->Valid())prefetch_iter_->Next();
+      prefetch_threads[i]=std::thread([this,&q,&lock,&cv,&local_stop_flag,&remaining_task_cnt,&main_finish]() 
+        {
+          Slice val;
+          int pos;
+          while(1){
+            lock->Lock();
+            while(q.empty()&&!local_stop_flag&&!(remaining_task_cnt==0&&main_finish)){
+              cv->Wait();
+            }
+            if(local_stop_flag||(remaining_task_cnt==0&&main_finish)){
+              cv->SignalAll();
+              lock->Unlock();
+              break;
+            }
+            std::string s=q.front().first;
+            pos=q.front().second;
+            q.pop();
+            remaining_task_cnt--;
+            lock->Unlock();
+            val=GetAndParseTrueValue(s);
+            prefetch_array[pos]=val;
+            prefetched_array[pos].store(true);
           }
-          pos+=prefetch_num_+1;
         }
-      });
+      );
+    }
+    Slice val;
+    int pos=0;
+    for(int i=0;i<100&&prefetch_iter_->Valid();i++){
+      prefetch_iter_->Next();
+      pos++;
     }
+    for(;prefetch_iter_->Valid()&&!stop_flag.load()&&pos<1000000;prefetch_iter_->Next()){
+      val=prefetch_iter_->value();
+      lock->Lock();
+      q.push({std::string(val.data(),val.size()),pos});
+      cv->Signal();
+      remaining_task_cnt++;
+      lock->Unlock();
+      pos++;
+    }
+
+    lock->Lock();
+    main_finish=true;
+    while(remaining_task_cnt){
+      cv->Wait();
+    }
+    lock->Unlock();
+    cv->SignalAll();
 
     for (auto& thread : prefetch_threads) {
         if (thread.joinable()) {
             thread.join();
         }
     }
-
-    
   }
 
    void PreFetchThreadBackward(){
     std::thread prefetch_threads[prefetch_num_];
+    std::queue<std::pair<std::string,int>> q;
+    port::Mutex* lock=new port::Mutex();
+    port::CondVar* cv=new port::CondVar(lock);
+    bool local_stop_flag=false;
+    int remaining_task_cnt=0;
+    bool main_finish=false;
     for(int i=0;i<prefetch_num_;i++){
-      Iterator* prefetch_iter_=prefetch_iters_[i];
-      int skip_num=i;
-      prefetch_threads[i]=std::thread([this,prefetch_iter_,skip_num]() {
-        int pos=1000000-skip_num;
-        for(int j=0;j<skip_num;j++){
-          if(prefetch_iter_->Valid())prefetch_iter_->Prev();
-        }
-        while(prefetch_iter_->Valid()){
-          Slice key_=prefetch_iter_->key();
-          std::string str_key=std::string(key_.data(),key_.size());
-          Slice val=GetAndParseTrueValue(prefetch_iter_);
-          if(stop_flag.load()||pos<0){
-            break;
-          }
-          prefetch_array[pos]=val;
-          prefetched_array[pos].store(true);
-          for(int j=0;j<prefetch_num_;j++){
-            if(prefetch_iter_->Valid())prefetch_iter_->Prev();
+      prefetch_threads[i]=std::thread([this,&q,&lock,&cv,&local_stop_flag,&remaining_task_cnt,&main_finish]() 
+        {
+          Slice val;
+          int pos;
+          while(1){
+            lock->Lock();
+            while(q.empty()&&!local_stop_flag&&!(remaining_task_cnt==0&&main_finish)){
+              cv->Wait();
+            }
+            if(local_stop_flag||(remaining_task_cnt==0&&main_finish)){
+              cv->SignalAll();
+              lock->Unlock();
+              break;
+            }
+            std::string s=q.front().first;
+            pos=q.front().second;
+            q.pop();
+            remaining_task_cnt--;
+            lock->Unlock();
+            val=GetAndParseTrueValue(s);
+            prefetch_array[pos]=val;
+            prefetched_array[pos].store(true);
           }
-          pos-=prefetch_num_+1;
         }
-      });
+      );
     }
+    Slice val;
+    int pos=1000000;
+    for(;prefetch_iter_->Valid()&&!stop_flag.load()&&pos>=0;prefetch_iter_->Prev()){
+      val=prefetch_iter_->value();
+      lock->Lock();
+      q.push({std::string(val.data(),val.size()),pos});
+      cv->Signal();
+      remaining_task_cnt++;
+      lock->Unlock();
+      pos--;
+    }
+
+    lock->Lock();
+    main_finish=true;
+    while(remaining_task_cnt){
+      cv->Wait();
+    }
+    lock->Unlock();
+    cv->SignalAll();
 
     for (auto& thread : prefetch_threads) {
         if (thread.joinable()) {
@@ -171,9 +238,8 @@ class DBPreFetchIter : public Iterator {
   
   DBImpl* db_;
   Iterator* const iter_;
-  std::vector<Iterator*> const prefetch_iters_;
+  Iterator* const prefetch_iter_;
   int prefetch_num_;
-  IterPos iter_pos_;
   std::atomic<bool> stop_flag;
   Slice prefetch_array[1000005];
   std::atomic<bool> prefetched_array[1000005];
@@ -191,15 +257,15 @@ void DBPreFetchIter::Prev() {
 
 void DBPreFetchIter::Seek(const Slice& target) {
   iter_->Seek(target);
-  cur_pos=0;
-  for(auto prefetch_iter_:prefetch_iters_)
-    prefetch_iter_->Seek(target);
+  
   if(prefetch_thread.joinable()){
     stop_flag.store(true);
     prefetch_thread.join();
-    for(int i=0;i<1000000;i++)prefetched_array[i]=false;
     stop_flag=false;
   }
+  for(int i=0;i<=1000000;i++)prefetched_array[i]=false;
+  cur_pos=0;
+  prefetch_iter_->Seek(target);
   prefetch_thread=std::thread([this]() {
       PreFetchThreadForward();
   });
@@ -207,37 +273,38 @@ void DBPreFetchIter::Seek(const Slice& target) {
 
 void DBPreFetchIter::SeekToFirst() {
   iter_->SeekToFirst();
-  cur_pos=0;
-  for(auto prefetch_iter_:prefetch_iters_)
-    prefetch_iter_->SeekToFirst();
+  
   if(prefetch_thread.joinable()){
     stop_flag.store(true);
     prefetch_thread.join();
-    for(int i=0;i<1000000;i++)prefetched_array[i]=false;
     stop_flag=false;
   }
+  for(int i=0;i<=1000000;i++)prefetched_array[i]=false;
+  cur_pos=0;
+  prefetch_iter_->SeekToFirst();
   prefetch_thread=std::thread([this]() {
       PreFetchThreadForward();
   });
   }
 void DBPreFetchIter::SeekToLast() {
   iter_->SeekToLast();
-  cur_pos=1000000;
-  for(auto prefetch_iter_:prefetch_iters_)
-    prefetch_iter_->SeekToLast();
+  
   if(prefetch_thread.joinable()){
     stop_flag.store(true);
     prefetch_thread.join();
-    for(int i=0;i<1000000;i++)prefetched_array[i]=false;
     stop_flag=false;
   }
+  for(int i=0;i<=1000000;i++)prefetched_array[i]=false;
+  cur_pos=1000000;
+  
   prefetch_thread=std::thread([this]() {
+      prefetch_iter_->SeekToLast();
       PreFetchThreadBackward();
   });
 }
 
 }  // anonymous namespace
-Iterator* NewPreFetchIterator(DBImpl* db,Iterator* db_iter,std::vector<Iterator*> prefetch_iters,int prefetch_num) {
-  return new DBPreFetchIter(db,db_iter,prefetch_iters,prefetch_num);
+Iterator* NewPreFetchIterator(DBImpl* db,Iterator* db_iter,Iterator* prefetch_iter,int prefetch_num) {
+  return new DBPreFetchIter(db,db_iter,prefetch_iter,prefetch_num);
 }
 }  // namespace leveldb
diff --git a/db/prefetch_iter.h b/db/prefetch_iter.h
index 74e8aec..133a773 100644
--- a/db/prefetch_iter.h
+++ b/db/prefetch_iter.h
@@ -15,7 +15,7 @@ namespace leveldb {
 class DBImpl;
 
 // add a prefetch function for db_iter
-Iterator* NewPreFetchIterator(DBImpl* db,Iterator* db_iter,std::vector<Iterator*> prefetch_iter,int prefetch_num);
+Iterator* NewPreFetchIterator(DBImpl* db,Iterator* db_iter, Iterator* prefetch_iter,int prefetch_num);
 
 }  // namespace leveldb
 
diff --git a/test/test.cpp b/test/test.cpp
index 08ec745..675fd46 100644
--- a/test/test.cpp
+++ b/test/test.cpp
@@ -43,9 +43,6 @@ TEST(Test, checkIterator) {
     for(int i=0;i<5000;i++){
         assert(iter->Valid());
         auto value=iter->value();
-        if(value!=values[i]){
-            std::cout<<std::string(value.data(),value.size())<<std::endl;
-        }
         assert(values[i]==value);
         iter->Next();
     }
@@ -54,9 +51,6 @@ TEST(Test, checkIterator) {
     for(int i=4999;i>=0;i--){
         assert(iter->Valid());
         auto value=iter->value();
-        if(value!=values[i]){
-            std::cout<<std::string(value.data(),value.size())<<std::endl;
-        }
         assert(values[i]==value);
         iter->Prev();
     }
@@ -65,9 +59,6 @@ TEST(Test, checkIterator) {
     for(int i=4990;i<5000;i++){
         assert(iter->Valid());
         auto value=iter->value();
-        if(value!=values[i]){
-            std::cout<<std::string(value.data(),value.size())<<std::endl;
-        }
         assert(values[i]==value);
         iter->Next();
     }
@@ -76,76 +67,76 @@ TEST(Test, checkIterator) {
     delete db;
 }
 
-// TEST(Test, CheckGetFields) {
-//     DB *db;
-//     WriteOptions writeOptions;
-//     ReadOptions readOptions;
-//     if(OpenDB("testdb_for_XOY", &db).ok() == false) {
-//         std::cerr << "open db failed" << std::endl;
-//         abort();
-//     }
-//     std::string key1 = "k_1";
+TEST(Test, CheckGetFields) {
+    DB *db;
+    WriteOptions writeOptions;
+    ReadOptions readOptions;
+    if(OpenDB("testdb_for_XOY", &db).ok() == false) {
+        std::cerr << "open db failed" << std::endl;
+        abort();
+    }
+    std::string key1 = "k_1";
     
-//     FieldArray fields1 = {
-//         {"name", "Customer#000000001"},
-//         {"address", "IVhzIApeRb"}, 
-//         {"phone", "25-989-741-2988"}
-//     };
+    FieldArray fields1 = {
+        {"name", "Customer#000000001"},
+        {"address", "IVhzIApeRb"}, 
+        {"phone", "25-989-741-2988"}
+    };
 
-//     auto value1=SerializeValue(fields1);
+    auto value1=SerializeValue(fields1);
 
-//     db->Put(WriteOptions(), key1, value1);
+    db->Put(WriteOptions(), key1, value1);
 
-//     std::string value_ret;
-//     FieldArray res1;
+    std::string value_ret;
+    FieldArray res1;
 
-//     db->Get(ReadOptions(), key1, &value_ret);
-//     DeserializeValue(value_ret, &res1);
-//     for(auto pr:res1){
-//         std::cout<<std::string(pr.first.data(),pr.first.size())<<" "<<std::string(pr.second.data(),pr.second.size())<<"\n";
-//     }
-//     ASSERT_TRUE(CompareFieldArray(fields1, res1));
+    db->Get(ReadOptions(), key1, &value_ret);
+    DeserializeValue(value_ret, &res1);
+    for(auto pr:res1){
+        std::cout<<std::string(pr.first.data(),pr.first.size())<<" "<<std::string(pr.second.data(),pr.second.size())<<"\n";
+    }
+    ASSERT_TRUE(CompareFieldArray(fields1, res1));
 
-//     db->Delete(WriteOptions(),key1);
+    db->Delete(WriteOptions(),key1);
     
-//     std::cout<<"get serialized value done"<<std::endl;
-//     delete db;
-
-// }
-
-// TEST(Test, CheckSearchKey) {
-//     DB *db;
-//     ReadOptions readOptions;
-//     if(OpenDB("testdb_for_XOY", &db).ok() == false) {
-//         std::cerr << "open db failed" << std::endl;
-//         abort();
-//     }
-//     std::vector<std::string> keys;
-//     std::vector<std::string> target_keys;
-//     for(int i=0;i<10000;i++){
-//       std::string key=std::to_string(rand()%10000)+"_"+std::to_string(i);//random for generate nonincreasing keys
-//       FieldArray fields={
-//         {"name", key},
-//         {"address", std::to_string(rand()%7)}, 
-//         {"phone", std::to_string(rand()%114514)}
-//       };
-//       if(rand()%5==0){
-//         fields[0].second="special_key";
-//         target_keys.push_back(key);
-//       }
-//       keys.push_back(key);
-//       db->Put(WriteOptions(),key,SerializeValue(fields));
-//     }
-//     std::sort(target_keys.begin(),target_keys.end());
-//     std::vector<std::string> key_res;
-//     Get_keys_by_field(db,ReadOptions(),{"name", "special_key"},&key_res);
-//     ASSERT_TRUE(CompareKey(key_res, target_keys));
-//     std::cout<<"get key by field done"<<std::endl;
-//     for(auto s:keys){
-//       db->Delete(WriteOptions(),s);
-//     }
-//     delete db;
-// }
+    std::cout<<"get serialized value done"<<std::endl;
+    delete db;
+
+}
+
+TEST(Test, CheckSearchKey) {
+    DB *db;
+    ReadOptions readOptions;
+    if(OpenDB("testdb_for_XOY", &db).ok() == false) {
+        std::cerr << "open db failed" << std::endl;
+        abort();
+    }
+    std::vector<std::string> keys;
+    std::vector<std::string> target_keys;
+    for(int i=0;i<10000;i++){
+      std::string key=std::to_string(rand()%10000)+"_"+std::to_string(i);//random for generate nonincreasing keys
+      FieldArray fields={
+        {"name", key},
+        {"address", std::to_string(rand()%7)}, 
+        {"phone", std::to_string(rand()%114514)}
+      };
+      if(rand()%5==0){
+        fields[0].second="special_key";
+        target_keys.push_back(key);
+      }
+      keys.push_back(key);
+      db->Put(WriteOptions(),key,SerializeValue(fields));
+    }
+    std::sort(target_keys.begin(),target_keys.end());
+    std::vector<std::string> key_res;
+    Get_keys_by_field(db,ReadOptions(),{"name", "special_key"},&key_res);
+    ASSERT_TRUE(CompareKey(key_res, target_keys));
+    std::cout<<"get key by field done"<<std::endl;
+    for(auto s:keys){
+      db->Delete(WriteOptions(),s);
+    }
+    delete db;
+}
 
 TEST(Test, LARGE_DATA_COMPACT_TEST) {
     DB *db;
@@ -179,42 +170,42 @@ TEST(Test, LARGE_DATA_COMPACT_TEST) {
     delete db;
 }
 
-// TEST(Test, Garbage_Collect_TEST) {
-//     DB *db;
-//     WriteOptions writeOptions;
-//     ReadOptions readOptions;
-//     if(OpenDB("testdb_for_XOY_large", &db).ok() == false) {
-//         std::cerr << "open db failed" << std::endl;
-//         abort();
-//     }
-//     std::vector<std::string> values;
-//     for(int i=0;i<5000;i++){
-//         std::string key=std::to_string(i);
-//         std::string value;
-//         for(int j=0;j<1000;j++){
-//             value+=std::to_string(i);
-//         }
-//         values.push_back(value);
-//         db->Put(writeOptions,key,value);
-//     }
-//     std::cout<<"start gc"<<std::endl;
-//     db->TEST_GarbageCollect();
-//     std::cout<<"finish gc"<<std::endl;
-
-//     for(int i=0;i<5000;i++){
-//         // std::cout<<i<<std::endl;
-//         std::string key=std::to_string(i);
-//         std::string value;
-//         Status s=db->Get(readOptions,key,&value);
-//         assert(s.ok());
-//         if(values[i]!=value){
-//             std::cout<<value.size()<<std::endl;
-//             assert(0);
-//         }
-//         ASSERT_TRUE(values[i]==value);
-//     }
-//     delete db;
-// }
+TEST(Test, Garbage_Collect_TEST) {
+    DB *db;
+    WriteOptions writeOptions;
+    ReadOptions readOptions;
+    if(OpenDB("testdb_for_XOY_large", &db).ok() == false) {
+        std::cerr << "open db failed" << std::endl;
+        abort();
+    }
+    std::vector<std::string> values;
+    for(int i=0;i<5000;i++){
+        std::string key=std::to_string(i);
+        std::string value;
+        for(int j=0;j<1000;j++){
+            value+=std::to_string(i);
+        }
+        values.push_back(value);
+        db->Put(writeOptions,key,value);
+    }
+    std::cout<<"start gc"<<std::endl;
+    db->TEST_GarbageCollect();
+    std::cout<<"finish gc"<<std::endl;
+
+    for(int i=0;i<5000;i++){
+        // std::cout<<i<<std::endl;
+        std::string key=std::to_string(i);
+        std::string value;
+        Status s=db->Get(readOptions,key,&value);
+        assert(s.ok());
+        if(values[i]!=value){
+            std::cout<<value.size()<<std::endl;
+            assert(0);
+        }
+        ASSERT_TRUE(values[i]==value);
+    }
+    delete db;
+}
 
 
 int main(int argc, char** argv) {