diff --git a/db/db_impl_add_file.cc b/db/db_impl_add_file.cc
index 3019f3391..a27108791 100644
--- a/db/db_impl_add_file.cc
+++ b/db/db_impl_add_file.cc
@@ -22,21 +22,6 @@
 
 namespace rocksdb {
 
-namespace {
-// RAII Timer
-class StatsTimer {
- public:
-  explicit StatsTimer(Env* env, uint64_t* counter)
-      : env_(env), counter_(counter), start_micros_(env_->NowMicros()) {}
-  ~StatsTimer() { *counter_ += env_->NowMicros() - start_micros_; }
-
- private:
-  Env* env_;
-  uint64_t* counter_;
-  uint64_t start_micros_;
-};
-}  // anonymous namespace
-
 #ifndef ROCKSDB_LITE
 
 Status DBImpl::ReadExternalSstFileInfo(ColumnFamilyHandle* column_family,
@@ -127,7 +112,6 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
     return Status::InvalidArgument("The list of files is empty");
   }
 
-  std::vector<ExternalSstFileInfo> file_infos(num_files);
   std::vector<ExternalSstFileInfo> file_info_list(num_files);
   for (size_t i = 0; i < num_files; i++) {
     status = ReadExternalSstFileInfo(column_family, file_path_list[i],
@@ -178,7 +162,7 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
   std::vector<uint64_t> micro_list(num_files, 0);
   std::vector<FileMetaData> meta_list(num_files);
   for (size_t i = 0; i < num_files; i++) {
-    StatsTimer t(env_, &micro_list[i]);
+    StopWatch sw(env_, nullptr, 0, &micro_list[i], false);
     if (file_info_list[i].num_entries == 0) {
       return Status::InvalidArgument("File contain no entries");
     }
@@ -212,7 +196,7 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
   {
     InstrumentedMutexLock l(&mutex_);
     for (size_t i = 0; i < num_files; i++) {
-      StatsTimer t(env_, &micro_list[i]);
+      StopWatch sw(env_, nullptr, 0, &micro_list[i], false);
       pending_outputs_inserted_elem_list[i] =
           CaptureCurrentFileNumberInPendingOutputs();
       meta_list[i].fd = FileDescriptor(versions_->NewFileNumber(), 0,
@@ -224,7 +208,7 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
   std::vector<std::string> db_fname_list(num_files);
   size_t j = 0;
   for (; j < num_files; j++) {
-    StatsTimer t(env_, &micro_list[j]);
+    StopWatch sw(env_, nullptr, 0, &micro_list[j], false);
     db_fname_list[j] =
         TableFileName(db_options_.db_paths, meta_list[j].fd.GetNumber(),
                       meta_list[j].fd.GetPathId());
@@ -275,7 +259,7 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
       ScopedArenaIterator iter(NewInternalIterator(ro, cfd, sv, &arena));
 
       for (size_t i = 0; i < num_files; i++) {
-        StatsTimer t(env_, &micro_list[i]);
+        StopWatch sw(env_, nullptr, 0, &micro_list[i], false);
         InternalKey range_start(file_info_list[i].smallest_key,
                                 kMaxSequenceNumber, kTypeValue);
         iter->Seek(range_start.Encode());
@@ -298,14 +282,13 @@ Status DBImpl::AddFile(ColumnFamilyHandle* column_family,
       }
     }
 
-    // The level the file will be ingested into
+    // The levels that the files will be ingested into
     std::vector<int> target_level_list(num_files, 0);
     if (status.ok()) {
-      // Add files to L0
       VersionEdit edit;
       edit.SetColumnFamily(cfd->GetID());
       for (size_t i = 0; i < num_files; i++) {
-        StatsTimer t(env_, &micro_list[i]);
+        StopWatch sw(env_, nullptr, 0, &micro_list[i], false);
         // Add file to the lowest possible level
         target_level_list[i] = PickLevelForIngestedFile(cfd, file_info_list[i]);
         edit.AddFile(target_level_list[i], meta_list[i].fd.GetNumber(),
diff --git a/include/rocksdb/db.h b/include/rocksdb/db.h
index 60ce7984a..accf41d9d 100644
--- a/include/rocksdb/db.h
+++ b/include/rocksdb/db.h
@@ -810,9 +810,9 @@ class DB {
   //
   // Current Requirements:
   // (1) The key ranges of the files don't overlap with each other
-  // (1) The key range of any file in list doesn't overlap with
+  // (2) The key range of any file in list doesn't overlap with
   //     existing keys or tombstones in DB.
-  // (2) No snapshots are held.
+  // (3) No snapshots are held.
   //
   // Notes: We will try to ingest the files to the lowest possible level
   //        even if the file compression dont match the level compression
diff --git a/util/stop_watch.h b/util/stop_watch.h
index 663661aba..bf2f6ebd0 100644
--- a/util/stop_watch.h
+++ b/util/stop_watch.h
@@ -10,25 +10,28 @@
 namespace rocksdb {
 // Auto-scoped.
 // Records the measure time into the corresponding histogram if statistics
-// is not nullptr. It is also saved into *elapsed if the pointer is not nullptr.
+// is not nullptr. It is also saved into *elapsed if the pointer is not nullptr
+// and overwrite is true, it will be added to *elapsed if overwrite is false.
 class StopWatch {
  public:
-  StopWatch(Env * const env, Statistics* statistics,
-            const uint32_t hist_type,
-            uint64_t* elapsed = nullptr)
-    : env_(env),
-      statistics_(statistics),
-      hist_type_(hist_type),
-      elapsed_(elapsed),
-      stats_enabled_(statistics && statistics->HistEnabledForType(hist_type)),
-      start_time_((stats_enabled_ || elapsed != nullptr) ?
-                  env->NowMicros() : 0) {
-  }
-
+  StopWatch(Env* const env, Statistics* statistics, const uint32_t hist_type,
+            uint64_t* elapsed = nullptr, bool overwrite = true)
+      : env_(env),
+        statistics_(statistics),
+        hist_type_(hist_type),
+        elapsed_(elapsed),
+        overwrite_(overwrite),
+        stats_enabled_(statistics && statistics->HistEnabledForType(hist_type)),
+        start_time_((stats_enabled_ || elapsed != nullptr) ? env->NowMicros()
+                                                           : 0) {}
 
   ~StopWatch() {
     if (elapsed_) {
-      *elapsed_ = env_->NowMicros() - start_time_;
+      if (overwrite_) {
+        *elapsed_ = env_->NowMicros() - start_time_;
+      } else {
+        *elapsed_ += env_->NowMicros() - start_time_;
+      }
     }
     if (stats_enabled_) {
       statistics_->measureTime(hist_type_,
@@ -42,6 +45,7 @@ class StopWatch {
   Statistics* statistics_;
   const uint32_t hist_type_;
   uint64_t* elapsed_;
+  bool overwrite_;
   bool stats_enabled_;
   const uint64_t start_time_;
 };