diff --git a/db/db_impl.cc b/db/db_impl.cc
index 3a5c225..06f8e61 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -1249,7 +1249,11 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {
     // into mem_.
     {
       mutex_.Unlock();
-      status = log_->AddRecord(WriteBatchInternal::Contents(write_batch));
+      // 先写入vlog再写入memtable
+      // 写vlog日志 offset 表示这个 write_batch 在vlog中的偏移地址。
+      uint64_t offset = 0;
+      status = vlog_->AddRecord(WriteBatchInternal::Contents(write_batch),offset);
+      // status = log_->AddRecord(WriteBatchInternal::Contents(write_batch));
       bool sync_error = false;
       if (status.ok() && options.sync) {
         status = logfile_->Sync();
@@ -1258,7 +1262,7 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {
         }
       }
       if (status.ok()) {
-        status = WriteBatchInternal::InsertInto(write_batch, mem_);
+        status = WriteBatchInternal::InsertInto(write_batch, mem_, logfile_number_, offset);
       }
       mutex_.Lock();
       if (sync_error) {
diff --git a/db/db_impl.h b/db/db_impl.h
index 91f4fd4..81db57d 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -12,6 +12,7 @@
 
 #include "db/dbformat.h"
 #include "db/log_writer.h"
+#include "db/vlog_writer.h"
 #include "db/snapshot.h"
 #include "leveldb/db.h"
 #include "leveldb/env.h"
@@ -207,6 +208,8 @@ class DBImpl : public DB {
   Status bg_error_ GUARDED_BY(mutex_);
 
   CompactionStats stats_[config::kNumLevels] GUARDED_BY(mutex_);
+
+  log::VlogWriter* vlog_;
 };
 
 // Sanitize db options.  The caller should delete result.info_log if
diff --git a/db/vlog_writer.cc b/db/vlog_writer.cc
new file mode 100644
index 0000000..b07e2bc
--- /dev/null
+++ b/db/vlog_writer.cc
@@ -0,0 +1,45 @@
+#include "db/vlog_writer.h"
+
+#include <cstdint>
+
+#include "leveldb/env.h"
+
+#include "util/coding.h"
+#include "util/crc32c.h"
+
+namespace leveldb {
+namespace log {
+VlogWriter::VlogWriter(WritableFile* dest) : dest_(dest), head_(0) {}
+
+VlogWriter::VlogWriter(WritableFile* dest, uint64_t dest_length)
+    : dest_(dest), head_(0) {}
+
+VlogWriter::~VlogWriter() = default;
+
+Status VlogWriter::AddRecord(const Slice& slice, uint64_t& offset) {
+  const char* ptr = slice.data();
+  size_t left = slice.size();
+  Status s;
+  s = EmitPhysicalRecord(ptr, left, offset);
+  return s;
+}
+
+Status VlogWriter::EmitPhysicalRecord(const char* ptr, size_t length,
+                                      uint64_t& offset) {
+  assert(length <= 0xffff);
+  char buf[4];
+  EncodeFixed32(buf, length);
+  Status s = dest_->Append(Slice(buf, 4));
+  if (s.ok()) {
+    s = dest_->Append(Slice(ptr, length));
+    if (s.ok()) {
+      s = dest_->Flush();
+      offset = head_ + 4;
+      head_ += 4 + length;
+    }
+  }
+  return s;
+}
+
+}  // namespace log
+}  // namespace leveldb
diff --git a/db/vlog_writer.h b/db/vlog_writer.h
new file mode 100644
index 0000000..9cb2313
--- /dev/null
+++ b/db/vlog_writer.h
@@ -0,0 +1,44 @@
+#ifndef LEVELDB_DB_VLOG_WRITER_H_
+#define LEVELDB_DB_VLOG_WRITER_H_
+
+#include "db/log_format.h"
+#include <cstdint>
+
+#include "leveldb/slice.h"
+#include "leveldb/status.h"
+
+namespace leveldb {
+
+class WritableFile;
+
+namespace log {
+
+class VlogWriter {
+ public:
+  // Create a writer that will append data to "*dest".
+  // "*dest" must be initially empty.
+  // "*dest" must remain live while this Writer is in use.
+  explicit VlogWriter(WritableFile* dest);
+
+  // Create a writer that will append data to "*dest".
+  // "*dest" must have initial length "dest_length".
+  // "*dest" must remain live while this Writer is in use.
+  VlogWriter(WritableFile* dest, uint64_t dest_length);
+
+  VlogWriter(const VlogWriter&) = delete;
+  VlogWriter& operator=(const VlogWriter&) = delete;
+
+  VlogWriter();
+
+  Status AddRecord(const Slice& slice, uint64_t& offset);
+
+ private:
+  Status EmitPhysicalRecord(const char* ptr, size_t length, uint64_t& offset);
+  size_t head_;
+  WritableFile* dest_;
+};
+
+}  // namespace log
+}  // namespace leveldb
+
+#endif  // LEVELDB_DB_VLOG_WRITER_H_
diff --git a/db/write_batch.cc b/db/write_batch.cc
index b54313c..874bc34 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -18,7 +18,9 @@
 #include "db/dbformat.h"
 #include "db/memtable.h"
 #include "db/write_batch_internal.h"
+
 #include "leveldb/db.h"
+
 #include "util/coding.h"
 
 namespace leveldb {
@@ -79,6 +81,68 @@ 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;
+  while (!input.empty()) {
+    found++;
+    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) {
+      case kTypeValue:
+        if (GetLengthPrefixedSlice(&input, &key) &&
+            GetLengthPrefixedSlice(&input, &value)) {
+          handler->Put(key, value);
+        } else {
+          return Status::Corruption("bad WriteBatch Put");
+        }
+        break;
+      case kTypeDeletion:
+        if (GetLengthPrefixedSlice(&input, &key)) {
+          handler->Delete(key);
+        } else {
+          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;
+      default:
+        return Status::Corruption("unknown WriteBatch tag");
+    }
+  }
+  if (found != WriteBatchInternal::Count(this)) {
+    return Status::Corruption("WriteBatch has wrong count");
+  } else {
+    return Status::OK();
+  }
+}
 int WriteBatchInternal::Count(const WriteBatch* b) {
   return DecodeFixed32(b->rep_.data() + 8);
 }
@@ -136,6 +200,15 @@ Status WriteBatchInternal::InsertInto(const WriteBatch* b, MemTable* memtable) {
   return b->Iterate(&inserter);
 }
 
+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);
+}
+
 void WriteBatchInternal::SetContents(WriteBatch* b, const Slice& contents) {
   assert(contents.size() >= kHeader);
   b->rep_.assign(contents.data(), contents.size());
diff --git a/db/write_batch_internal.h b/db/write_batch_internal.h
index fce86e3..dd08be8 100644
--- a/db/write_batch_internal.h
+++ b/db/write_batch_internal.h
@@ -37,6 +37,8 @@ class WriteBatchInternal {
 
   static Status InsertInto(const WriteBatch* batch, MemTable* memtable);
 
+  static Status InsertInto(const WriteBatch* batch, MemTable* memtable,uint64_t fid, size_t offset);
+
   static void Append(WriteBatch* dst, const WriteBatch* src);
 };
 
diff --git a/include/leveldb/write_batch.h b/include/leveldb/write_batch.h
index 94d4115..2af98a3 100644
--- a/include/leveldb/write_batch.h
+++ b/include/leveldb/write_batch.h
@@ -71,6 +71,7 @@ class LEVELDB_EXPORT WriteBatch {
 
   // Support for iterating over the contents of a batch.
   Status Iterate(Handler* handler) const;
+  Status Iterate(Handler* handler, uint64_t fid, uint64_t offset) const;
 
  private:
   friend class WriteBatchInternal;