diff --git a/CMakeLists.txt b/CMakeLists.txt
index 627a08a..f61882e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -31,6 +31,7 @@ if(STATUS_LENGTH EQUAL 0)
 else()
   add_definitions(-DGIT_COMMIT_HASH="[developing]")
 endif()
+add_definitions(-DZSTD_STATIC_LINKING_ONLY)
 
 # 设置一个布尔类型的选项，用于控制是否启用高级功能，如日志（业务日志、程序日志、容错校验日志）、并发、快照等
 option(ENABLE_ADVANCED_FEATURE "Enable advanced features" OFF)
diff --git a/dataguard/include/dataguard/snapshot.h b/dataguard/include/dataguard/snapshot.h
index c8803f5..40136c3 100644
--- a/dataguard/include/dataguard/snapshot.h
+++ b/dataguard/include/dataguard/snapshot.h
@@ -4,6 +4,8 @@
 #include "map.hpp"
 #include "storage/driver.h"
 #include "vector.hpp"
+void GenerateDiff(const std::string &old_file, const std::string &new_file, const std::string &diff_file);
+void ApplyPatch(const std::string &old_file, const std::string &diff_file, const std::string &new_file, bool is_reverse);
 class SnapShotManager {
   bool has_connected = false;
   sjtu::vector<DataDriverBase *> drivers;
diff --git a/dataguard/src/snapshot.cpp b/dataguard/src/snapshot.cpp
index f46d56d..e5ca522 100644
--- a/dataguard/src/snapshot.cpp
+++ b/dataguard/src/snapshot.cpp
@@ -1,2 +1,280 @@
 #include "dataguard/snapshot.h"
+#include <sys/stat.h>
 #include <zstd.h>
+#include <cstdint>
+#include "storage/config.h"
+#include "vector.hpp"
+
+default_numeric_index_t GetFileSize(const std::string &file) {
+  struct stat stat_buf;
+  int rc = stat(file.c_str(), &stat_buf);
+  if (rc != 0) {
+    throw std::runtime_error("stat failed");
+  }
+  return stat_buf.st_size;
+}
+struct uint8_t_reader {
+  FILE *f;
+  uint8_t *buf, *p1, *p2;
+  int size;
+  uint8_t_reader(FILE *fin, int bufsize = 1 << 12) {
+    f = fin;
+    size = bufsize;
+    p1 = p2 = 0;
+    buf = new uint8_t[size];
+  }
+  ~uint8_t_reader() { delete[] buf; }
+  inline int operator()() { return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, size, f), p1 == p2) ? EOF : *p1++; }
+};
+struct uint8_t_writer {
+  FILE *f;
+  uint8_t *buf, *p, *end;
+  int size;
+  uint8_t_writer(FILE *fout, int bufsize = 1 << 12) {
+    f = fout;
+    size = bufsize;
+    buf = new uint8_t[size];
+    p = buf;
+    end = buf + bufsize;
+  }
+  void Flush() {
+    fwrite(buf, p - buf, 1, f);
+    p = buf;
+  }
+  ~uint8_t_writer() {
+    fwrite(buf, p - buf, 1, f);
+    delete[] buf;
+  }
+  inline uint8_t operator()(uint8_t ch) {
+    if (end == p) [[unlikely]] {
+      fwrite(buf, end - buf, 1, f);
+      p = buf;
+    }
+    return *p++ = ch;
+  }
+};
+void GenerateDiff(const std::string &old_file, const std::string &new_file, const std::string &diff_file) {
+  /**
+   * Step 1: compare content of old_file and new_file, write it to buf
+   * Step 2: use zstd to compress buf, write it to diff_file
+   */
+  sjtu::vector<uint8_t> buf;
+  // Step 1
+  default_numeric_index_t old_file_size = GetFileSize(old_file);
+  default_numeric_index_t new_file_size = GetFileSize(new_file);
+  default_numeric_index_t shared_size = std::min(old_file_size, new_file_size);
+  bool current_is_diff = false;
+  default_numeric_index_t current_diff_len = 0, current_diff_pos = 0;
+  sjtu::vector<uint8_t> diff_buff_in_old, diff_buff_in_new;
+  FILE *old_fp = fopen(old_file.c_str(), "rb");
+  FILE *new_fp = fopen(new_file.c_str(), "rb");
+  uint8_t_reader old_reader(old_fp), new_reader(new_fp);
+  for (size_t i = 0; i < shared_size; i++) {
+    uint8_t o_c = old_reader(), n_c = new_reader();
+    if (o_c == n_c) {
+      if (current_is_diff) {
+        buf.push_back(0);
+        buf.push_back((current_diff_len >> 24) & 0xFF);
+        buf.push_back((current_diff_len >> 16) & 0xFF);
+        buf.push_back((current_diff_len >> 8) & 0xFF);
+        buf.push_back(current_diff_len & 0xFF);
+        buf.push_back((current_diff_pos >> 24) & 0xFF);
+        buf.push_back((current_diff_pos >> 16) & 0xFF);
+        buf.push_back((current_diff_pos >> 8) & 0xFF);
+        buf.push_back(current_diff_pos & 0xFF);
+        for (uint8_t c : diff_buff_in_old) {
+          buf.push_back(c);
+        }
+        for (uint8_t c : diff_buff_in_new) {
+          buf.push_back(c);
+        }
+        current_is_diff = false;
+        current_diff_len = 0;
+        diff_buff_in_old.clear();
+        diff_buff_in_new.clear();
+      } else {
+        continue;
+      }
+    } else {
+      if (current_is_diff) {
+        diff_buff_in_old.push_back(o_c);
+        diff_buff_in_new.push_back(n_c);
+        current_diff_len++;
+      } else {
+        current_is_diff = true;
+        current_diff_len = 1;
+        current_diff_pos = i;
+        diff_buff_in_old.push_back(o_c);
+        diff_buff_in_new.push_back(n_c);
+      }
+    }
+  }
+  if (current_is_diff) {
+    buf.push_back(0);
+    buf.push_back((current_diff_len >> 24) & 0xFF);
+    buf.push_back((current_diff_len >> 16) & 0xFF);
+    buf.push_back((current_diff_len >> 8) & 0xFF);
+    buf.push_back(current_diff_len & 0xFF);
+    buf.push_back((current_diff_pos >> 24) & 0xFF);
+    buf.push_back((current_diff_pos >> 16) & 0xFF);
+    buf.push_back((current_diff_pos >> 8) & 0xFF);
+    buf.push_back(current_diff_pos & 0xFF);
+    for (uint8_t c : diff_buff_in_old) {
+      buf.push_back(c);
+    }
+    for (uint8_t c : diff_buff_in_new) {
+      buf.push_back(c);
+    }
+  }
+  if (old_file_size > shared_size) {
+    buf.push_back(1);
+    for (size_t i = shared_size; i < old_file_size; i++) {
+      buf.push_back(old_reader());
+    }
+  }
+  if (new_file_size > shared_size) {
+    buf.push_back(2);
+    for (size_t i = shared_size; i < new_file_size; i++) {
+      buf.push_back(new_reader());
+    }
+  }
+  // Step 2
+  size_t compressed_size_bound = ZSTD_compressBound(buf.size());
+  uint8_t *compressed_buf = new uint8_t[compressed_size_bound];
+  size_t compressed_size = ZSTD_compress(compressed_buf, compressed_size_bound, buf.data(), buf.size(), 12);
+  if (ZSTD_isError(compressed_size)) {
+    delete[] compressed_buf;
+    throw std::runtime_error(ZSTD_getErrorName(compressed_size));
+  }
+  FILE *fp = fopen(diff_file.c_str(), "wb");
+  if (fp == nullptr) {
+    delete[] compressed_buf;
+    throw std::runtime_error("fopen failed");
+  }
+  fwrite(compressed_buf, 1, compressed_size, fp);
+  fclose(fp);
+  delete[] compressed_buf;
+}
+void ApplyPatch(const std::string &old_file, const std::string &diff_file, const std::string &new_file,
+                bool is_reverse) {
+  default_numeric_index_t compressed_size = GetFileSize(diff_file);
+  uint8_t *compressed_buf = new uint8_t[compressed_size + 5];
+  FILE *fp = fopen(diff_file.c_str(), "rb");
+  fread(compressed_buf, 1, compressed_size, fp);
+  fclose(fp);
+  size_t decompressed_buf_size = ZSTD_decompressBound(compressed_buf, compressed_size);
+  uint8_t *decompressed_buf = new uint8_t[decompressed_buf_size];
+  size_t decompressed_size = ZSTD_decompress(decompressed_buf, decompressed_buf_size, compressed_buf, compressed_size);
+  if (ZSTD_isError(decompressed_size)) {
+    delete[] compressed_buf;
+    delete[] decompressed_buf;
+    throw std::runtime_error(ZSTD_getErrorName(decompressed_size));
+  }
+  delete[] compressed_buf;
+  fp = fopen(old_file.c_str(), "rb");
+  size_t old_file_size = GetFileSize(old_file);
+  FILE *fp2 = fopen(new_file.c_str(), "wb");
+  uint8_t_reader reader(fp);
+  uint8_t_writer writer(fp2);
+  size_t diff_buf_cnt = 0;
+  size_t reader_cursor = 0;
+  while (diff_buf_cnt < decompressed_size) {
+    uint8_t flag;
+    flag = decompressed_buf[diff_buf_cnt++];
+    if (flag == 0) {
+      default_numeric_index_t current_diff_len = 0, current_diff_pos = 0, tmp = 0;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_len |= tmp << 24;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_len |= tmp << 16;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_len |= tmp << 8;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_len |= tmp;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_pos |= tmp << 24;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_pos |= tmp << 16;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_pos |= tmp << 8;
+      tmp = decompressed_buf[diff_buf_cnt++];
+      current_diff_pos |= tmp;
+      while (reader_cursor < current_diff_pos) {
+        writer(reader());
+        reader_cursor++;
+      }
+      uint8_t *old_buf = new uint8_t[current_diff_len];
+      uint8_t *new_buf = new uint8_t[current_diff_len];
+      for (size_t i = 0; i < current_diff_len; i++) {
+        old_buf[i] = decompressed_buf[diff_buf_cnt++];
+      }
+      for (size_t i = 0; i < current_diff_len; i++) {
+        new_buf[i] = decompressed_buf[diff_buf_cnt++];
+      }
+      if (!is_reverse) {
+        for (size_t i = 0; i < current_diff_len; i++) {
+          writer(new_buf[i]);
+          reader_cursor++;
+          reader();
+        }
+      } else {
+        for (size_t i = 0; i < current_diff_len; i++) {
+          writer(old_buf[i]);
+          reader_cursor++;
+          reader();
+        }
+      }
+      delete[] old_buf;
+      delete[] new_buf;
+    } else if (flag == 1) {
+      size_t delta_len = decompressed_size - diff_buf_cnt;
+      if (!is_reverse) {
+        // Just make the last bytes disappear
+        while (reader_cursor < old_file_size - delta_len) {
+          writer(reader());
+          reader_cursor++;
+        }
+        goto ed;
+      } else {
+        while (reader_cursor < old_file_size) {
+          writer(reader());
+          reader_cursor++;
+        }
+        while (diff_buf_cnt < decompressed_size) {
+          writer(decompressed_buf[diff_buf_cnt++]);
+        }
+        goto ed;
+      }
+    } else if (flag == 2) {
+      size_t delta_len = decompressed_size - diff_buf_cnt;
+      if (is_reverse) {
+        // Just make the last bytes disappear
+        while (reader_cursor < old_file_size - delta_len) {
+          writer(reader());
+          reader_cursor++;
+        }
+        goto ed;
+      } else {
+        while (reader_cursor < old_file_size) {
+          writer(reader());
+          reader_cursor++;
+        }
+        while (diff_buf_cnt < decompressed_size) {
+          writer(decompressed_buf[diff_buf_cnt++]);
+        }
+        goto ed;
+      }
+    }
+  }
+  if (reader_cursor < old_file_size) {
+    while (reader_cursor < old_file_size) {
+      writer(reader());
+      reader_cursor++;
+    }
+  }
+ed:;
+  writer.Flush();
+  fclose(fp);
+  fclose(fp2);
+  delete[] decompressed_buf;
+}
\ No newline at end of file
diff --git a/stlite/vector.hpp b/stlite/vector.hpp
index 8a9aea9..cfe2b52 100644
--- a/stlite/vector.hpp
+++ b/stlite/vector.hpp
@@ -534,6 +534,8 @@ class vector {
     //   allocated_length = new_allocated_length;
     // }
   }
+
+  T *data() { return raw_beg; }
 };
 template <typename T>
 std::allocator<T> vector<T>::alloc;
diff --git a/storage/include/storage/disk_map.hpp b/storage/include/storage/disk_map.hpp
index 3b3c401..358210a 100644
--- a/storage/include/storage/disk_map.hpp
+++ b/storage/include/storage/disk_map.hpp
@@ -68,11 +68,15 @@ class DiskMap : public DataDriverBase {
     return true;
   }
   bool Put(const Key &key, Value &value) {
-    if (indexer->Put(key, data_storage->preview_next_blank())) {
-      data_storage->write(value);
-      return true;
+    b_plus_tree_value_index_t data_id;
+    data_id = indexer->Get(key);
+    if (data_id != kInvalidValueIndex) {
+      data_storage->update(value, data_id);
+      return false;
     }
-    return false;
+    data_id = data_storage->write(value);
+    indexer->Put(key, data_id);
+    return true;
   }
 };
 #endif  // DISK_MAP_H
\ No newline at end of file
diff --git a/storage/include/storage/single_value_storage.hpp b/storage/include/storage/single_value_storage.hpp
index c60d635..77d6c0c 100644
--- a/storage/include/storage/single_value_storage.hpp
+++ b/storage/include/storage/single_value_storage.hpp
@@ -60,18 +60,18 @@ class SingleValueStorage {
     memcpy(raw_mem + n * sizeof(int), &tmp, sizeof(int));
   }
 
-  size_t preview_next_blank() {
-    if (first_blank_element_pair_id != 0) return first_blank_element_pair_id;
-    frame_id_t frame_id;
-    BasicPageGuard guard = bpm->NewPageGuarded(&frame_id);
-    first_blank_element_pair_id = frame_id * max_element_in_page;
-    for (size_t i = 0; i < max_element_in_page - 1; i++) {
-      guard.AsMut<Page>()->dat.elements[i].nxt_blank = first_blank_element_pair_id + i + 1;
-    }
-    guard.AsMut<Page>()->dat.elements[max_element_in_page - 1].nxt_blank = 0;
-    guard.AsMut<Page>()->dat.elements_count = 0;
-    return first_blank_element_pair_id;
-  }
+  // size_t preview_next_blank() {
+  //   if (first_blank_element_pair_id != 0) return first_blank_element_pair_id;
+  //   frame_id_t frame_id;
+  //   BasicPageGuard guard = bpm->NewPageGuarded(&frame_id);
+  //   first_blank_element_pair_id = frame_id * max_element_in_page;
+  //   for (size_t i = 0; i < max_element_in_page - 1; i++) {
+  //     guard.AsMut<Page>()->dat.elements[i].nxt_blank = first_blank_element_pair_id + i + 1;
+  //   }
+  //   guard.AsMut<Page>()->dat.elements[max_element_in_page - 1].nxt_blank = 0;
+  //   guard.AsMut<Page>()->dat.elements_count = 0;
+  //   return first_blank_element_pair_id;
+  // }
   int write(T &t) {
     size_t element_id = first_blank_element_pair_id;
     size_t res_id = 0;
diff --git a/test/snapshot_test.cpp b/test/snapshot_test.cpp
index 34df0b1..d5cb608 100644
--- a/test/snapshot_test.cpp
+++ b/test/snapshot_test.cpp
@@ -44,12 +44,12 @@ TEST(Basic, DiskMap) {
   std::map<int, int> std_map;
   remove("/tmp/index.db");
   remove("/tmp/data.db");
-  const int total_opts = 10;
+  const int total_opts = 1000000;
   {
     DiskMap<int, int> disk_map("index", "/tmp/index.db", "data", "/tmp/data.db");
     for (int i = 0; i < total_opts; i++) {
       int opt_id = rnd() % 100;
-      if (opt_id <= 30) {
+      if (opt_id <= 40) {
         if (keys_container.Size() > 0 && rnd() % 5 <= 2) {
           // overrite and existing key
           int key = keys_container.GetRandomKey(rnd);
@@ -90,4 +90,42 @@ TEST(Basic, DiskMap) {
       }
     }
   }
+}
+
+TEST(Basic, T1) {
+  remove("/tmp/1.dat");
+  remove("/tmp/2.dat");
+  remove("/tmp/diff.dat");
+  remove("/tmp/3.dat");
+  remove("/tmp/4.dat");
+  const unsigned int RndSeed = testing::GTEST_FLAG(random_seed);
+  std::mt19937 rnd(RndSeed);
+  const int str_len_s1 = 10000;
+  const int str_len_s2 = 9900;
+  char s1[str_len_s1], s2[str_len_s2];
+  for (int i = 0; i < str_len_s1 - 1; i++) {
+    s1[i] = 'a' + rnd() % 26;
+  }
+  s1[str_len_s1 - 1] = '\0';
+  memcpy(s2, s1, str_len_s2);
+  for (int i = 0; i < str_len_s2 - 1; i++) {
+    if (i >= str_len_s1) {
+      s2[i] = 'a' + rnd() % 26;
+      continue;
+    }
+    if (rnd() % 3 == 0) {
+      s2[i] = 'a' + rnd() % 26;
+    }
+  }
+  s2[str_len_s2 - 1] = '\0';
+  // write to file
+  FILE *fp = fopen("/tmp/1.dat", "wb");
+  fwrite(s1, 1, str_len_s1, fp);
+  fclose(fp);
+  fp = fopen("/tmp/2.dat", "wb");
+  fwrite(s2, 1, str_len_s2, fp);
+  fclose(fp);
+  GenerateDiff("/tmp/1.dat", "/tmp/2.dat", "/tmp/diff.dat");
+  ApplyPatch("/tmp/1.dat", "/tmp/diff.dat", "/tmp/3.dat", false);
+  ApplyPatch("/tmp/2.dat", "/tmp/diff.dat", "/tmp/4.dat", true);
 }
\ No newline at end of file