diff --git a/db/db_impl.cc b/db/db_impl.cc
index a5e7153..946f3b9 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -146,11 +146,14 @@ DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
       has_imm_(false),
       logfile_(nullptr),
       logfile_number_(0),
-      log_(nullptr),
       seed_(0),
       tmp_batch_(new WriteBatch),
       background_compaction_scheduled_(false),
       manual_compaction_(nullptr),
+
+      vlog_(nullptr),
+      vlog_kv_numbers_(0),
+
       versions_(new VersionSet(dbname_, &options_, table_cache_,
                                &internal_comparator_)) {}
 
@@ -171,7 +174,7 @@ DBImpl::~DBImpl() {
   if (mem_ != nullptr) mem_->Unref();
   if (imm_ != nullptr) imm_->Unref();
   delete tmp_batch_;
-  delete log_;
+  delete vlog_;
   delete logfile_;
   delete table_cache_;
 
@@ -476,13 +479,13 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
   // See if we should keep reusing the last log file.
   if (status.ok() && options_.reuse_logs && last_log && compactions == 0) {
     assert(logfile_ == nullptr);
-    assert(log_ == nullptr);
+    assert(vlog_ == nullptr);
     assert(mem_ == nullptr);
     uint64_t lfile_size;
     if (env_->GetFileSize(fname, &lfile_size).ok() &&
         env_->NewAppendableFile(fname, &logfile_).ok()) {
       Log(options_.info_log, "Reusing old log %s \n", fname.c_str());
-      log_ = new log::Writer(logfile_, lfile_size);
+      vlog_ = new log::VlogWriter(logfile_, lfile_size);
       logfile_number_ = log_number;
       if (mem != nullptr) {
         mem_ = mem;
@@ -1313,6 +1316,9 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {
     WriteBatchInternal::SetSequence(write_batch, last_sequence + 1);
     last_sequence += WriteBatchInternal::Count(write_batch);
 
+    /* TODO */
+    vlog_kv_numbers_ += WriteBatchInternal::Count(write_batch);
+
     // Add to log and apply to memtable.  We can release the lock
     // during this phase since &w is currently responsible for logging
     // and protects against concurrent loggers and concurrent writes
@@ -1423,6 +1429,23 @@ Status DBImpl::MakeRoomForWrite(bool force) {
   assert(!writers_.empty());
   bool allow_delay = !force;
   Status s;
+
+  if (logfile_->GetSize() > options_.max_value_log_size) {
+    uint64_t new_log_number = versions_->NewFileNumber();
+    WritableFile* lfile = nullptr;
+    s = env_->NewWritableFile(LogFileName(dbname_, new_log_number), &lfile);
+    if (!s.ok()) {
+      versions_->ReuseFileNumber(new_log_number);
+    }
+//    gc_management_->WriteFileMap(logfile_number_, vlog_kv_numbers_, logfile_->GetSize());
+    vlog_kv_numbers_ = 0;
+    delete vlog_;
+    delete logfile_;
+    logfile_ = lfile;
+    logfile_number_ = new_log_number;
+    vlog_ = new log::VlogWriter(lfile);
+  }
+
   while (true) {
     if (!bg_error_.ok()) {
       // Yield previous error
@@ -1456,33 +1479,9 @@ Status DBImpl::MakeRoomForWrite(bool force) {
     } else {
       // Attempt to switch to a new memtable and trigger compaction of old
       assert(versions_->PrevLogNumber() == 0);
-      uint64_t new_log_number = versions_->NewFileNumber();
-      WritableFile* lfile = nullptr;
-      s = env_->NewWritableFile(LogFileName(dbname_, new_log_number), &lfile);
-      if (!s.ok()) {
-        // Avoid chewing through file number space in a tight loop.
-        versions_->ReuseFileNumber(new_log_number);
-        break;
-      }
 
-      delete log_;
+      mem_->SetLogFileNumber(logfile_number_);
 
-      s = logfile_->Close();
-      if (!s.ok()) {
-        // We may have lost some data written to the previous log file.
-        // Switch to the new log file anyway, but record as a background
-        // error so we do not attempt any more writes.
-        //
-        // We could perhaps attempt to save the memtable corresponding
-        // to log file and suppress the error if that works, but that
-        // would add more complexity in a critical code path.
-        RecordBackgroundError(s);
-      }
-      delete logfile_;
-
-      logfile_ = lfile;
-      logfile_number_ = new_log_number;
-      log_ = new log::Writer(lfile);
       imm_ = mem_;
       has_imm_.store(true, std::memory_order_release);
       mem_ = new MemTable(internal_comparator_);
@@ -1577,7 +1576,7 @@ void DBImpl::GetApproximateSizes(const Range* range, int n, uint64_t* sizes) {
 // 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) {
-  WriteBatch batch;
+  WriteBatch batch(opt.separate_threshold);
   batch.Put(key, value);
   return Write(opt, &batch);
 }
@@ -1609,7 +1608,7 @@ Status DB::Open(const Options& options, const std::string& dbname, DB** dbptr) {
       edit.SetLogNumber(new_log_number);
       impl->logfile_ = lfile;
       impl->logfile_number_ = new_log_number;
-      impl->log_ = new log::Writer(lfile);
+      impl->vlog_ = new log::VlogWriter(lfile);
       impl->mem_ = new MemTable(impl->internal_comparator_);
       impl->mem_->Ref();
     }
diff --git a/db/db_impl.h b/db/db_impl.h
index 2237a72..46a8993 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -186,7 +186,7 @@ class DBImpl : public DB {
   std::atomic<bool> has_imm_;         // So bg thread can detect non-null imm_
   WritableFile* logfile_;
   uint64_t logfile_number_ GUARDED_BY(mutex_);
-  log::Writer* log_;
+//  log::VlogWriter* log_;
   uint32_t seed_ GUARDED_BY(mutex_);  // For sampling.
 
   // Queue of writers.
@@ -212,6 +212,10 @@ class DBImpl : public DB {
   CompactionStats stats_[config::kNumLevels] GUARDED_BY(mutex_);
 
   log::VlogWriter* vlog_;
+
+  int vlog_kv_numbers_;
+
+//  KVSepManagement* gc_management_;
 };
 
 // Sanitize db options.  The caller should delete result.info_log if
diff --git a/db/db_iter.cc b/db/db_iter.cc
index 532c2db..b83948b 100644
--- a/db/db_iter.cc
+++ b/db/db_iter.cc
@@ -189,6 +189,7 @@ void DBIter::FindNextUserEntry(bool skipping, std::string* skip) {
           skipping = true;
           break;
         case kTypeValue:
+        case kTypeSeparation:
           if (skipping &&
               user_comparator_->Compare(ikey.user_key, *skip) <= 0) {
             // Entry hidden
diff --git a/db/db_test.cc b/db/db_test.cc
index a4a84cd..98cac55 100644
--- a/db/db_test.cc
+++ b/db/db_test.cc
@@ -190,6 +190,7 @@ class SpecialEnv : public EnvWrapper {
         }
         return base_->Sync();
       }
+      size_t GetSize() { return base_->GetSize(); }
     };
     class ManifestFile : public WritableFile {
      private:
@@ -215,6 +216,7 @@ class SpecialEnv : public EnvWrapper {
           return base_->Sync();
         }
       }
+      size_t GetSize() { return base_->GetSize(); }
     };
 
     if (non_writable_.load(std::memory_order_acquire)) {
diff --git a/db/dumpfile.cc b/db/dumpfile.cc
index 6085475..76a15c6 100644
--- a/db/dumpfile.cc
+++ b/db/dumpfile.cc
@@ -74,7 +74,7 @@ Status PrintLogContents(Env* env, const std::string& fname,
 // Called on every item found in a WriteBatch.
 class WriteBatchItemPrinter : public WriteBatch::Handler {
  public:
-  void Put(const Slice& key, const Slice& value) override {
+  void Put(const Slice& key, const Slice& value, ValueType type = kTypeValue) override {
     std::string r = "  put '";
     AppendEscapedStringTo(&r, key);
     r += "' '";
@@ -189,6 +189,8 @@ Status DumpTable(Env* env, const std::string& fname, WritableFile* dst) {
         r += "del";
       } else if (key.type == kTypeValue) {
         r += "val";
+      } else if (key.type == kTypeSeparation) {
+        r += "val";
       } else {
         AppendNumberTo(&r, key.type);
       }
diff --git a/db/fault_injection_test.cc b/db/fault_injection_test.cc
index ef864a4..cbc5cfd 100644
--- a/db/fault_injection_test.cc
+++ b/db/fault_injection_test.cc
@@ -114,6 +114,7 @@ class TestWritableFile : public WritableFile {
   Status Close() override;
   Status Flush() override;
   Status Sync() override;
+  size_t GetSize() override { return 0; };
 
  private:
   FileState state_;
diff --git a/db/leveldbutil.cc b/db/leveldbutil.cc
index 95ee897..9980c02 100644
--- a/db/leveldbutil.cc
+++ b/db/leveldbutil.cc
@@ -20,6 +20,7 @@ class StdoutPrinter : public WritableFile {
   Status Close() override { return Status::OK(); }
   Status Flush() override { return Status::OK(); }
   Status Sync() override { return Status::OK(); }
+  size_t GetSize() override { return 0; }
 };
 
 bool HandleDumpCommand(Env* env, char** files, int num) {
diff --git a/db/log_test.cc b/db/log_test.cc
index d55d4dd..73e3844 100644
--- a/db/log_test.cc
+++ b/db/log_test.cc
@@ -164,6 +164,7 @@ class LogTest : public testing::Test {
     Status Close() override { return Status::OK(); }
     Status Flush() override { return Status::OK(); }
     Status Sync() override { return Status::OK(); }
+    size_t GetSize() override { return 0; }
     Status Append(const Slice& slice) override {
       contents_.append(slice.data(), slice.size());
       return Status::OK();
diff --git a/db/memtable.cc b/db/memtable.cc
index 4f09340..c09b51d 100644
--- a/db/memtable.cc
+++ b/db/memtable.cc
@@ -126,9 +126,16 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) {
           value->assign(v.data(), v.size());
           return true;
         }
-        case kTypeDeletion:
+        case kTypeDeletion: {
           *s = Status::NotFound(Slice());
           return true;
+        }
+        case kTypeSeparation: {
+          Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
+          value->assign(v.data(), v.size());
+          s->SetSeparated();
+          return true;
+        }
       }
     }
   }
diff --git a/db/memtable.h b/db/memtable.h
index 9d986b1..0ce2087 100644
--- a/db/memtable.h
+++ b/db/memtable.h
@@ -62,6 +62,10 @@ class MemTable {
   // Else, return false.
   bool Get(const LookupKey& key, std::string* value, Status* s);
 
+  uint64_t GetTailSequence() { return tail_sequence_; }
+  uint64_t GetLogFileNumber() { return log_file_number_; }
+  uint64_t SetLogFileNumber(uint64_t fid) { log_file_number_ = fid; }
+
  private:
   friend class MemTableIterator;
   friend class MemTableBackwardIterator;
@@ -76,6 +80,9 @@ class MemTable {
 
   ~MemTable();  // Private since only Unref() should be used to delete it
 
+  uint64_t tail_sequence_;
+  uint64_t log_file_number_;
+
   KeyComparator comparator_;
   int refs_;
   Arena arena_;
diff --git a/db/write_batch.cc b/db/write_batch.cc
index 874bc34..ef95a35 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -9,20 +9,18 @@
 // record :=
 //    kTypeValue varstring varstring         |
 //    kTypeDeletion varstring
+//    kTypeSeparation varstring varstring
 // varstring :=
 //    len: varint32
 //    data: uint8[len]
 
 #include "leveldb/write_batch.h"
 
-#include "db/dbformat.h"
 #include "db/memtable.h"
 #include "db/write_batch_internal.h"
 
 #include "leveldb/db.h"
 
-#include "util/coding.h"
-
 namespace leveldb {
 
 // WriteBatch header has an 8-byte sequence number followed by a 4-byte count.
@@ -84,13 +82,11 @@ Status WriteBatch::Iterate(Handler* handler) const {
 Status WriteBatch::Iterate(Handler* handler, uint64_t fid,
                            uint64_t offset) const {
   Slice input(rep_);
-  // 整个writebatch 的起始地址
   const char* begin = input.data();
 
   if (input.size() < kHeader) {
     return Status::Corruption("malformed WriteBatch (too small)");
   }
-  // 12个字节，8个字节用来表示sequence，4个字节用来表示 count，移除头
   input.remove_prefix(kHeader);
   Slice key, value;
   int found = 0;
@@ -99,8 +95,6 @@ Status WriteBatch::Iterate(Handler* handler, uint64_t fid,
     const uint64_t kv_offset = input.data() - begin + offset;
     assert(kv_offset > 0);
 
-    // record 记录为  1 个字节 是 kTypeValue ,剩下的字节是 key value
-    // record 记录为  1 个字节 是 kTypeDeletion， 剩下的字节是key
     char tag = input[0];
     input.remove_prefix(1);
     switch (tag) {
@@ -119,20 +113,20 @@ Status WriteBatch::Iterate(Handler* handler, uint64_t fid,
           return Status::Corruption("bad WriteBatch Delete");
         }
         break;
-      // case kTypeSeparate:
-      //   if (GetLengthPrefixedSlice(&input, &key) &&
-      //       GetLengthPrefixedSlice(&input, &(value))) {
-      //     // value = fileNumber + offset + valuesize 采用变长编码的方式
-      //     std::string dest;
-      //     PutVarint64(&dest, fid);
-      //     PutVarint64(&dest, kv_offset);
-      //     PutVarint64(&dest, value.size());
-      //     Slice value_offset(dest);
-      //     handler->Put(key, value_offset, kTypeSeparate);
-      //   } else {
-      //     return Status::Corruption("bad WriteBatch Put");
-      //   }
-      //   break;
+      case kTypeSeparation:
+        if (GetLengthPrefixedSlice(&input, &key) &&
+             GetLengthPrefixedSlice(&input, &(value))) {
+          // value = fileNumber + offset + valuesize 采用变长编码的方式
+          std::string dest;
+          PutVarint64(&dest, fid);
+          PutVarint64(&dest, kv_offset);
+          PutVarint64(&dest, value.size());
+          Slice value_offset(dest);
+          handler->Put(key, value_offset, kTypeSeparation);
+        } else {
+          return Status::Corruption("WriteBatch Put error");
+        }
+        break;
       default:
         return Status::Corruption("unknown WriteBatch tag");
     }
@@ -143,6 +137,7 @@ Status WriteBatch::Iterate(Handler* handler, uint64_t fid,
     return Status::OK();
   }
 }
+
 int WriteBatchInternal::Count(const WriteBatch* b) {
   return DecodeFixed32(b->rep_.data() + 8);
 }
@@ -161,7 +156,11 @@ void WriteBatchInternal::SetSequence(WriteBatch* b, SequenceNumber seq) {
 
 void WriteBatch::Put(const Slice& key, const Slice& value) {
   WriteBatchInternal::SetCount(this, WriteBatchInternal::Count(this) + 1);
-  rep_.push_back(static_cast<char>(kTypeValue));
+  if (value.size() >= separate_threshold_) {
+    rep_.push_back(static_cast<char>(kTypeSeparation));
+  } else {
+    rep_.push_back(static_cast<char>(kTypeValue));
+  }
   PutLengthPrefixedSlice(&rep_, key);
   PutLengthPrefixedSlice(&rep_, value);
 }
@@ -182,8 +181,8 @@ class MemTableInserter : public WriteBatch::Handler {
   SequenceNumber sequence_;
   MemTable* mem_;
 
-  void Put(const Slice& key, const Slice& value) override {
-    mem_->Add(sequence_, kTypeValue, key, value);
+  void Put(const Slice& key, const Slice& value, ValueType type = kTypeValue) override {
+    mem_->Add(sequence_, type, key, value);
     sequence_++;
   }
   void Delete(const Slice& key) override {
@@ -203,7 +202,6 @@ Status WriteBatchInternal::InsertInto(const WriteBatch* b, MemTable* memtable) {
 Status WriteBatchInternal::InsertInto(const WriteBatch* b, MemTable* memtable,
                                       uint64_t fid, size_t offset) {
   MemTableInserter inserter;
-  // 一批 writeBatch中只有一个sequence，公用的，后续会自加。
   inserter.sequence_ = WriteBatchInternal::Sequence(b);
   inserter.mem_ = memtable;
   return b->Iterate(&inserter, fid, offset);
diff --git a/helpers/memenv/memenv.cc b/helpers/memenv/memenv.cc
index e476613..8407924 100644
--- a/helpers/memenv/memenv.cc
+++ b/helpers/memenv/memenv.cc
@@ -199,17 +199,22 @@ class RandomAccessFileImpl : public RandomAccessFile {
 
 class WritableFileImpl : public WritableFile {
  public:
-  WritableFileImpl(FileState* file) : file_(file) { file_->Ref(); }
+  WritableFileImpl(FileState* file) : file_(file), file_size_(0) { file_->Ref(); }
 
   ~WritableFileImpl() override { file_->Unref(); }
 
-  Status Append(const Slice& data) override { return file_->Append(data); }
+  Status Append(const Slice& data) override {
+    file_size_+= data.size();
+    return file_->Append(data);
+  }
 
   Status Close() override { return Status::OK(); }
   Status Flush() override { return Status::OK(); }
   Status Sync() override { return Status::OK(); }
+  size_t GetSize() override { return file_size_; }
 
  private:
+  int file_size_;
   FileState* file_;
 };
 
diff --git a/include/leveldb/env.h b/include/leveldb/env.h
index e00895a..2f0dae3 100644
--- a/include/leveldb/env.h
+++ b/include/leveldb/env.h
@@ -287,6 +287,7 @@ class LEVELDB_EXPORT WritableFile {
   virtual Status Close() = 0;
   virtual Status Flush() = 0;
   virtual Status Sync() = 0;
+  virtual size_t GetSize() = 0;
 };
 
 // An interface for writing log messages.
diff --git a/include/leveldb/options.h b/include/leveldb/options.h
index e110c80..dd82879 100644
--- a/include/leveldb/options.h
+++ b/include/leveldb/options.h
@@ -148,7 +148,7 @@ struct LEVELDB_EXPORT Options {
 
   /* 需要再研究下 */
   // value log 的文件大小
-  uint64_t max_value_log_size = 500 * 1024 * 1024;
+  uint64_t max_value_log_size = 16 * 1024 * 1024;
   // gc 的回收阈值。
   uint64_t garbage_collection_threshold = max_value_log_size / 4;
   // gc 后台回收时候重新put的时候，默认的kv分离的值。
@@ -176,7 +176,9 @@ struct LEVELDB_EXPORT ReadOptions {
 
 // Options that control write operations
 struct LEVELDB_EXPORT WriteOptions {
-  WriteOptions() = default;
+  explicit WriteOptions(size_t separateThreshold = 16)
+      : separate_threshold(separateThreshold) {}
+//  WriteOptions() = default;
 
   // If true, the write will be flushed from the operating system
   // buffer cache (by calling WritableFile::Sync()) before the write
@@ -192,6 +194,7 @@ struct LEVELDB_EXPORT WriteOptions {
   // crash semantics as the "write()" system call.  A DB write
   // with sync==true has similar crash semantics to a "write()"
   // system call followed by "fsync()".
+  size_t separate_threshold ;
   bool sync = false;
 };
 
diff --git a/include/leveldb/write_batch.h b/include/leveldb/write_batch.h
index 2af98a3..c09ceb0 100644
--- a/include/leveldb/write_batch.h
+++ b/include/leveldb/write_batch.h
@@ -25,6 +25,7 @@
 
 #include "leveldb/export.h"
 #include "leveldb/status.h"
+#include "db/dbformat.h"
 
 namespace leveldb {
 
@@ -35,11 +36,13 @@ class LEVELDB_EXPORT WriteBatch {
   class LEVELDB_EXPORT Handler {
    public:
     virtual ~Handler();
-    virtual void Put(const Slice& key, const Slice& value) = 0;
+    virtual void Put(const Slice& key, const Slice& value, ValueType type = kTypeValue) = 0;
     virtual void Delete(const Slice& key) = 0;
   };
 
   WriteBatch();
+  explicit WriteBatch(size_t separate_threshold)
+      : separate_threshold_(separate_threshold) { Clear(); }
 
   // Intentionally copyable.
   WriteBatch(const WriteBatch&) = default;
@@ -75,7 +78,7 @@ class LEVELDB_EXPORT WriteBatch {
 
  private:
   friend class WriteBatchInternal;
-
+  size_t separate_threshold_;
   std::string rep_;  // See comment in write_batch.cc for the format of rep_
 };
 
diff --git a/table/table_test.cc b/table/table_test.cc
index aea0697..a924157 100644
--- a/table/table_test.cc
+++ b/table/table_test.cc
@@ -97,6 +97,7 @@ class StringSink : public WritableFile {
   Status Close() override { return Status::OK(); }
   Status Flush() override { return Status::OK(); }
   Status Sync() override { return Status::OK(); }
+  size_t GetSize(){ return contents_.size(); }
 
   Status Append(const Slice& data) override {
     contents_.append(data.data(), data.size());
diff --git a/util/env_posix.cc b/util/env_posix.cc
index ffd06c4..eb26480 100644
--- a/util/env_posix.cc
+++ b/util/env_posix.cc
@@ -279,6 +279,7 @@ class PosixWritableFile final : public WritableFile {
   PosixWritableFile(std::string filename, int fd)
       : pos_(0),
         fd_(fd),
+        file_size_(0),
         is_manifest_(IsManifest(filename)),
         filename_(std::move(filename)),
         dirname_(Dirname(filename_)) {}
@@ -290,10 +291,14 @@ class PosixWritableFile final : public WritableFile {
     }
   }
 
+  size_t GetSize() { return file_size_; }
+
   Status Append(const Slice& data) override {
     size_t write_size = data.size();
     const char* write_data = data.data();
 
+    file_size_ += write_size;
+
     // Fit as much as possible into buffer.
     size_t copy_size = std::min(write_size, kWritableFileBufferSize - pos_);
     std::memcpy(buf_ + pos_, write_data, copy_size);
@@ -459,6 +464,8 @@ class PosixWritableFile final : public WritableFile {
   size_t pos_;
   int fd_;
 
+  int file_size_;
+
   const bool is_manifest_;  // True if the file's name starts with MANIFEST.
   const std::string filename_;
   const std::string dirname_;  // The directory of filename_.