diff --git a/db/builder.cc b/db/builder.cc
index e6329e0..4c6d802 100644
--- a/db/builder.cc
+++ b/db/builder.cc
@@ -29,11 +29,17 @@ Status BuildTable(const std::string& dbname, Env* env, const Options& options,
     }
 
     TableBuilder* builder = new TableBuilder(options, file);
-    meta->smallest.DecodeFrom(iter->key());
+    meta->smallest.DecodeFrom(iter->key());//这里是internal_key
+//    auto tmp_ts = DecodeFixed64(iter->value().data() + iter->value().size() - kTSLength);
+//    meta->oldest_ts = tmp_ts;
+//    meta->newer_ts = tmp_ts;
     Slice key;
     for (; iter->Valid(); iter->Next()) {
       key = iter->key();
       builder->Add(key, iter->value());
+//      tmp_ts = DecodeFixed64(iter->value().data() + iter->value().size() - kTSLength);
+//      meta->oldest_ts = meta->oldest_ts > tmp_ts ? tmp_ts : meta->oldest_ts;
+//      meta->newer_ts = meta->newer_ts > tmp_ts ? meta->newer_ts : tmp_ts;
     }
     if (!key.empty()) {
       meta->largest.DecodeFrom(key);
diff --git a/db/db_impl.cc b/db/db_impl.cc
index 4d47e9e..b117cb1 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -510,7 +510,7 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit,
   Status s;
   {
     mutex_.Unlock();
-    s = BuildTable(dbname_, env_, options_, table_cache_, iter, &meta);
+    s = BuildTable(dbname_, env_, options_, table_cache_, iter, &meta);//meta包含largest_key,此时未刷盘meta，但meta.number对应生成的file会刷盘
     mutex_.Lock();
   }
 
@@ -588,6 +588,7 @@ void DBImpl::CompactRange(const Slice* begin, const Slice* end) {
   for (int level = 0; level < max_level_with_files; level++) {
     TEST_CompactRange(level, begin, end);
   }
+  TEST_CompactRange(max_level_with_files, begin, end);
 }
 
 void DBImpl::TEST_CompactRange(int level, const Slice* begin,
@@ -618,7 +619,7 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,
          bg_error_.ok()) {
     if (manual_compaction_ == nullptr) {  // Idle
       manual_compaction_ = &manual;
-      MaybeScheduleCompaction();
+      MaybeScheduleCompaction();//有可能寻址过多，导致allow_seek为0，触发合并。
     } else {  // Running either my compaction or another compaction.
       background_work_finished_signal_.Wait();
     }
@@ -1166,7 +1167,7 @@ Status DBImpl::Get(const ReadOptions& options, const Slice& key,
       auto t2 = GetTS(value);
       if(t1 >= t2){
         // 过期
-        s = Status::Expire("Expire",Slice());
+        s = Status::NotFound("NotFound",Slice());
       } else {
         // 没过期
         *value = value->substr(0, value->size() - sizeof(uint64_t));
@@ -1515,11 +1516,15 @@ void DBImpl::AppendTS(const Slice& val, std::string* val_with_ts,uint64_t ttl) {
  * @param val
  * @return timestamp in val,and remove timestamp from val
  */
-uint64_t DBImpl::GetTS(const std::string* val) {
-  // 不用auto再写一下
-    uint64_t expiration_time;
-    memcpy(&expiration_time, val->data() + val->size() - sizeof(uint64_t), sizeof(uint64_t));
-    return expiration_time;
+uint64_t DBImpl::GetTS(std::string* val) {
+  // 不用auto再写一下 老逻辑：
+    // uint64_t expiration_time;
+    // memcpy(&expiration_time, val->data() + val->size() - sizeof(uint64_t), sizeof(uint64_t));
+    // return expiration_time;
+  // 新逻辑：
+  auto expiration_time =  DecodeFixed64(val->data() + val->size() - kTSLength);
+  val->resize(val->size() - kTSLength);
+  return expiration_time;
 }
 
 // Default implementations of convenience methods that subclasses of DB
@@ -1535,14 +1540,18 @@ Status DB::Put(const WriteOptions& options, const Slice& key,
                    const Slice& value, uint64_t ttl) {
   // 将 value 和 expiration_time 合并到一起，形成带 TTL 的 value
   std::string val_with_ts;
-  val_with_ts.reserve(value.size() + sizeof(uint64_t));
+  val_with_ts.reserve(value.size() + kTSLength);
   uint64_t expiration_time = std::chrono::duration_cast<std::chrono::milliseconds>(
                                  std::chrono::system_clock::now().time_since_epoch())
                                  .count() + ttl * 1000;
+
+  char ts_string[kTSLength];
+  EncodeFixed64(ts_string, expiration_time);
   // 追加原始 value 到 val_with_ts
   val_with_ts.append(value.data(), value.size());
   // 将 expiration_time 追加到 val_with_ts
-  val_with_ts.append(reinterpret_cast<const char*>(&expiration_time), sizeof(expiration_time));
+  // val_with_ts.append(reinterpret_cast<const char*>(&expiration_time), sizeof(expiration_time));
+  val_with_ts.append(ts_string, kTSLength);
 //  std::cout<<"PUT"<<std::endl;
 //  std::cout << "timestamp: " << expiration_time << std::endl;
   //"a\323='\277\222\001\000"
diff --git a/db/db_impl.h b/db/db_impl.h
index 4c39042..5c5b2f5 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -49,7 +49,7 @@ class DBImpl : public DB {
   void GetApproximateSizes(const Range* range, int n, uint64_t* sizes) override;
   void CompactRange(const Slice* begin, const Slice* end) override;
   void AppendTS(const Slice& val, std::string* val_with_ts,uint64_t ttl);
-  static uint64_t GetTS(const std::string* val);
+  static uint64_t GetTS(std::string* val);
   // Extra methods (for testing) that are not in the public DB interface
 
   // Compact any files in the named level that overlap [*begin,*end]
diff --git a/db/dbformat.h b/db/dbformat.h
index 9e6a3ef..56f8178 100644
--- a/db/dbformat.h
+++ b/db/dbformat.h
@@ -26,15 +26,15 @@ static const int kNumLevels = 7;
 
 // Level-0 compaction is started when we hit this many files.
 // 这里修改了，改的比较大，原来是4
-static const int kL0_CompactionTrigger = 128;
+static const int kL0_CompactionTrigger = 64;
 
 // Soft limit on number of level-0 files.  We slow down writes at this point.
 // 这里修改了，改的比较大，原来是8
-static const int kL0_SlowdownWritesTrigger = 128;
+static const int kL0_SlowdownWritesTrigger = 64;
 
 // Maximum number of level-0 files.  We stop writes at this point.
 // 这里修改了，改的比较大，原来是12
-static const int kL0_StopWritesTrigger = 128;
+static const int kL0_StopWritesTrigger = 64;
 
 // Maximum level to which a new compacted memtable is pushed if it
 // does not create overlap.  We try to push to level 2 to avoid the
diff --git a/db/memtable.cc b/db/memtable.cc
index 7450b29..c561523 100644
--- a/db/memtable.cc
+++ b/db/memtable.cc
@@ -81,7 +81,7 @@ void MemTable::Add(SequenceNumber s, ValueType type, const Slice& key,
   //  key bytes    : char[internal_key.size()]
   //  tag          : uint64((sequence << 8) | type)
   //  value_size   : varint32 of value.size()
-  //  value bytes  : char[value.size()]
+  //  value bytes  : char[value.size()],[real_value,timestamp(uint64)]
   size_t key_size = key.size();
   size_t val_size = value.size();
   size_t internal_key_size = key_size + 8;
@@ -95,7 +95,7 @@ void MemTable::Add(SequenceNumber s, ValueType type, const Slice& key,
   EncodeFixed64(p, (s << 8) | type);
   p += 8;
   p = EncodeVarint32(p, val_size);
-  std::memcpy(p, value.data(), val_size);
+  std::memcpy(p, value.data(), val_size);//value包含timestamp,timestamp，8字节
   assert(p + val_size == buf + encoded_len);
   table_.Insert(buf);
 }
@@ -125,6 +125,23 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) {
         case kTypeValue: {
           Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
           value->assign(v.data(), v.size());
+
+          // 这里新加了一些逻辑
+          if (value->size() >= sizeof(uint64_t)){
+            const char* ptr = value->data();
+            std::string temp_str(value->data(), value->size());
+            uint64_t expiration_time = DBImpl::GetTS(&temp_str);
+            uint64_t current_time = std::chrono::duration_cast<std::chrono::milliseconds>(
+              std::chrono::system_clock::now().time_since_epoch())
+              .count();
+
+            if (current_time > expiration_time) {
+              *s = Status::NotFound("NotFound",Slice());
+            }else {
+              *value = value->substr(0, value->size() - sizeof(uint64_t));
+            }
+          }
+          
           return true;
         }
         case kTypeDeletion:
diff --git a/db/version_set.cc b/db/version_set.cc
index 4e37bf9..81b13e9 100644
--- a/db/version_set.cc
+++ b/db/version_set.cc
@@ -138,7 +138,7 @@ bool SomeFileOverlapsRange(const InternalKeyComparator& icmp,
     return false;
   }
 
-  // Binary search over file list
+  // Binary search over file list, 保证SSTable有序
   uint32_t index = 0;
   if (smallest_user_key != nullptr) {
     // Find the earliest possible internal key for smallest_user_key
@@ -351,6 +351,7 @@ Status Version::Get(const ReadOptions& options, const LookupKey& k,
       state->last_file_read = f;
       state->last_file_read_level = level;
 
+//      if(state->stats->now_ts > f->newer_ts)return false;
       state->s = state->vset->table_cache_->Get(*state->options, f->number,
                                                 f->file_size, state->ikey,
                                                 &state->saver, SaveValue);
@@ -460,7 +461,7 @@ void Version::Unref() {
     delete this;
   }
 }
-
+//files_[level] 中存在至少一个文件的键范围与 [smallest_user_key, largest_user_key] 有重叠，那么 OverlapInLevel 就会返回 true。
 bool Version::OverlapInLevel(int level, const Slice* smallest_user_key,
                              const Slice* largest_user_key) {
   return SomeFileOverlapsRange(vset_->icmp_, (level > 0), files_[level],
@@ -470,7 +471,7 @@ bool Version::OverlapInLevel(int level, const Slice* smallest_user_key,
 int Version::PickLevelForMemTableOutput(const Slice& smallest_user_key,
                                         const Slice& largest_user_key) {
   int level = 0;
-  if (!OverlapInLevel(0, &smallest_user_key, &largest_user_key)) {
+  if (!OverlapInLevel(0, &smallest_user_key, &largest_user_key)) {//当与level0没有重叠时，直接选择压入其他层
     // Push to next level if there is no overlap in next level,
     // and the #bytes overlapping in the level after that are limited.
     InternalKey start(smallest_user_key, kMaxSequenceNumber, kValueTypeForSeek);
@@ -664,7 +665,7 @@ class VersionSet::Builder {
       if (f->allowed_seeks < 100) f->allowed_seeks = 100;
 
       levels_[level].deleted_files.erase(f->number);
-      levels_[level].added_files->insert(f);
+      levels_[level].added_files->insert(f);//按照最小key排序
     }
   }
 
@@ -795,7 +796,7 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
     builder.Apply(edit);
     builder.SaveTo(v);
   }
-  Finalize(v);
+  Finalize(v);//对于每层compact打分
 
   // Initialize new descriptor log file if necessary by creating
   // a temporary file that contains a snapshot of the current version.
@@ -820,7 +821,7 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
     // Write new record to MANIFEST log
     if (s.ok()) {
       std::string record;
-      edit->EncodeTo(&record);
+      edit->EncodeTo(&record);// TODO:修改
       s = descriptor_log_->AddRecord(record);
       if (s.ok()) {
         s = descriptor_file_->Sync();
@@ -1386,7 +1387,7 @@ void VersionSet::SetupOtherInputs(Compaction* c) {
   const int level = c->level();
   InternalKey smallest, largest;
 
-  AddBoundaryInputs(icmp_, current_->files_[level], &c->inputs_[0]);
+  AddBoundaryInputs(icmp_, current_->files_[level], &c->inputs_[0]);//增加边界值,userkey相等的情况
   GetRange(c->inputs_[0], &smallest, &largest);
 
   current_->GetOverlappingInputs(level + 1, &smallest, &largest,
@@ -1444,11 +1445,11 @@ void VersionSet::SetupOtherInputs(Compaction* c) {
   compact_pointer_[level] = largest.Encode().ToString();
   c->edit_.SetCompactPointer(level, largest);
 }
-
+//得到基于当前level的所涉及的需要compact的文件,(level0可能会涉及到level1等)
 Compaction* VersionSet::CompactRange(int level, const InternalKey* begin,
                                      const InternalKey* end) {
   std::vector<FileMetaData*> inputs;
-  current_->GetOverlappingInputs(level, begin, end, &inputs);
+  current_->GetOverlappingInputs(level, begin, end, &inputs);//得到一层的input
   if (inputs.empty()) {
     return nullptr;
   }
diff --git a/db/version_set.h b/db/version_set.h
index ea0c925..7b96986 100644
--- a/db/version_set.h
+++ b/db/version_set.h
@@ -62,6 +62,7 @@ class Version {
   struct GetStats {
     FileMetaData* seek_file;
     int seek_file_level;
+    TIMESTAMP now_ts;
   };
 
   // Append to *iters a sequence of iterators that will
diff --git a/db/write_batch.cc b/db/write_batch.cc
index b54313c..5131cdb 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -99,7 +99,7 @@ void WriteBatch::Put(const Slice& key, const Slice& value) {
   WriteBatchInternal::SetCount(this, WriteBatchInternal::Count(this) + 1);
   rep_.push_back(static_cast<char>(kTypeValue));
   PutLengthPrefixedSlice(&rep_, key);
-  PutLengthPrefixedSlice(&rep_, value);
+  PutLengthPrefixedSlice(&rep_, value);//默认value的最大字节长度不会超过变长32位的表示。
 }
 
 void WriteBatch::Delete(const Slice& key) {
diff --git a/table/block.cc b/table/block.cc
index 3b15257..eae569a 100644
--- a/table/block.cc
+++ b/table/block.cc
@@ -220,7 +220,27 @@ class Block::Iter : public Iterator {
       if (!ParseNextKey()) {
         return;
       }
-      if (Compare(key_, target) >= 0) {
+      if (Compare(key_, target) >= 0) { // 找到了key_
+
+      // 这里新加了一些逻辑
+        std::string value(value_.data(), value_.size());
+        if (value.size() >= sizeof(uint64_t)){
+            const char* ptr = value.data();
+            std::string temp_str(value.data(), value.size());
+            uint64_t expiration_time =  DecodeFixed64((&temp_str)->data() + (&temp_str)->size() - sizeof(uint64_t));
+            (&temp_str)->resize((&temp_str)->size() - sizeof(uint64_t));
+
+            uint64_t current_time = std::chrono::duration_cast<std::chrono::milliseconds>(
+              std::chrono::system_clock::now().time_since_epoch())
+              .count();
+
+            if (current_time > expiration_time) {
+              status_ = Status::NotFound("NotFound",Slice());
+            }else {
+              value_ = value.substr(0, value.size() - sizeof(uint64_t));
+            }
+          }
+
         return;
       }
     }
diff --git a/table/table_builder.cc b/table/table_builder.cc
index 0932c94..d561eff 100644
--- a/table/table_builder.cc
+++ b/table/table_builder.cc
@@ -31,7 +31,8 @@ struct TableBuilder::Rep {
         filter_block(opt.filter_policy == nullptr
                          ? nullptr
                          : new FilterBlockBuilder(opt.filter_policy)),
-        pending_index_entry(false) {
+        pending_index_entry(false),
+        has_ttl_filter_(false){
     index_block_options.block_restart_interval = 1;
   }
 
@@ -57,6 +58,7 @@ struct TableBuilder::Rep {
   //
   // Invariant: r->pending_index_entry is true only if data_block is empty.
   bool pending_index_entry;
+  bool has_ttl_filter_;
   BlockHandle pending_handle;  // Handle to add to index block
 
   std::string compressed_output;
@@ -110,8 +112,12 @@ void TableBuilder::Add(const Slice& key, const Slice& value) {
 
   if (r->filter_block != nullptr) {
     r->filter_block->AddKey(key);
+//    if(r->has_ttl_filter_){
+//
+//    }
   }
 
+
   r->last_key.assign(key.data(), key.size());
   r->num_entries++;
   r->data_block.Add(key, value);
diff --git a/util/comparator.cc b/util/comparator.cc
index c5766e9..e1e8001 100644
--- a/util/comparator.cc
+++ b/util/comparator.cc
@@ -18,53 +18,53 @@ namespace leveldb {
 Comparator::~Comparator() = default;
 
 namespace {
-class BytewiseComparatorImpl : public Comparator {
- public:
-  BytewiseComparatorImpl() = default;
+  class BytewiseComparatorImpl : public Comparator {
+   public:
+    BytewiseComparatorImpl() = default;
 
-  const char* Name() const override { return "leveldb.BytewiseComparator"; }
+    const char* Name() const override { return "leveldb.BytewiseComparator"; }
 
-  int Compare(const Slice& a, const Slice& b) const override {
-    return a.compare(b);
-  }
-
-  void FindShortestSeparator(std::string* start,
-                             const Slice& limit) const override {
-    // Find length of common prefix
-    size_t min_length = std::min(start->size(), limit.size());
-    size_t diff_index = 0;
-    while ((diff_index < min_length) &&
-           ((*start)[diff_index] == limit[diff_index])) {
-      diff_index++;
+    int Compare(const Slice& a, const Slice& b) const override {
+      return a.compare(b);
     }
+    //最终生成的 start 将是一个有效的、更短的键，仍然在 limit 范围内；能够这么运行的前提：数据按key有序输入
+    void FindShortestSeparator(std::string* start,
+                               const Slice& limit) const override {
+      // Find length of common prefix
+      size_t min_length = std::min(start->size(), limit.size());
+      size_t diff_index = 0;
+      while ((diff_index < min_length) &&
+             ((*start)[diff_index] == limit[diff_index])) {
+        diff_index++;
+      }
 
-    if (diff_index >= min_length) {
-      // Do not shorten if one string is a prefix of the other
-    } else {
-      uint8_t diff_byte = static_cast<uint8_t>((*start)[diff_index]);
-      if (diff_byte < static_cast<uint8_t>(0xff) &&
-          diff_byte + 1 < static_cast<uint8_t>(limit[diff_index])) {
-        (*start)[diff_index]++;
-        start->resize(diff_index + 1);
-        assert(Compare(*start, limit) < 0);
+      if (diff_index >= min_length) {
+        // Do not shorten if one string is a prefix of the other
+      } else {
+        uint8_t diff_byte = static_cast<uint8_t>((*start)[diff_index]);
+        if (diff_byte < static_cast<uint8_t>(0xff) &&
+            diff_byte + 1 < static_cast<uint8_t>(limit[diff_index])) {
+          (*start)[diff_index]++;
+          start->resize(diff_index + 1);
+          assert(Compare(*start, limit) < 0);
+        }
       }
     }
-  }
 
-  void FindShortSuccessor(std::string* key) const override {
-    // Find first character that can be incremented
-    size_t n = key->size();
-    for (size_t i = 0; i < n; i++) {
-      const uint8_t byte = (*key)[i];
-      if (byte != static_cast<uint8_t>(0xff)) {
-        (*key)[i] = byte + 1;
-        key->resize(i + 1);
-        return;
+    void FindShortSuccessor(std::string* key) const override {
+      // Find first character that can be incremented
+      size_t n = key->size();
+      for (size_t i = 0; i < n; i++) {
+        const uint8_t byte = (*key)[i];
+        if (byte != static_cast<uint8_t>(0xff)) {
+          (*key)[i] = byte + 1;
+          key->resize(i + 1);
+          return;
+        }
       }
+      // *key is a run of 0xffs.  Leave it alone.
     }
-    // *key is a run of 0xffs.  Leave it alone.
-  }
-};
+  };
 }  // namespace
 
 const Comparator* BytewiseComparator() {