diff --git a/src/core/algorithm/diskann/diskann_builder.h b/src/core/algorithm/diskann/diskann_builder.h
index b8df7f5..edc80c4 100644
--- a/src/core/algorithm/diskann/diskann_builder.h
+++ b/src/core/algorithm/diskann/diskann_builder.h
@@ -28,28 +28,27 @@ class DiskAnnBuilder : public IndexBuilder {
   DiskAnnBuilder() = default;
 
   //! Initialize the builder
-  virtual int init(const IndexMeta &meta,
-                   const ailego::Params &params) override;
+  int init(const IndexMeta &meta, const ailego::Params &params) override;
 
   //! Cleanup the builder
-  virtual int cleanup(void) override;
+  int cleanup(void) override;
 
   //! Train the data
-  virtual int train(IndexThreads::Pointer threads,
-                    IndexHolder::Pointer holder) override;
+  int train(IndexThreads::Pointer threads,
+            IndexHolder::Pointer holder) override;
 
-  //! Train the data
-  virtual int train(const IndexTrainer::Pointer &trainer) override;
+  //! Train the data with trainer
+  int train(const IndexTrainer::Pointer &trainer) override;
 
   //! Build the index
-  virtual int build(IndexThreads::Pointer threads,
-                    IndexHolder::Pointer holder) override;
+  int build(IndexThreads::Pointer threads,
+            IndexHolder::Pointer holder) override;
 
   //! Dump index into storage
-  virtual int dump(const IndexDumper::Pointer &dumper) override;
+  int dump(const IndexDumper::Pointer &dumper) override;
 
   //! Retrieve statistics
-  virtual const Stats &stats(void) const override {
+  const Stats &stats(void) const override {
     return stats_;
   }
 
diff --git a/src/core/algorithm/diskann/diskann_context.h b/src/core/algorithm/diskann/diskann_context.h
index dd824ff..ce8c0ca 100644
--- a/src/core/algorithm/diskann/diskann_context.h
+++ b/src/core/algorithm/diskann/diskann_context.h
@@ -68,41 +68,40 @@ class DiskAnnContext : public IndexContext,
                      const DiskAnnEntity::Pointer &entity, uint32_t magic_num);
 
   //! Retrieve search result
-  virtual const IndexDocumentList &result(void) const override {
+  const IndexDocumentList &result(void) const override {
     return results_[0];
   }
 
   //! Retrieve search result
-  virtual const IndexDocumentList &result(size_t idx) const override {
+  const IndexDocumentList &result(size_t idx) const override {
     return results_[idx];
   }
 
   //! Retrieve result object for output
-  virtual IndexDocumentList *mutable_result(size_t idx) override {
+  IndexDocumentList *mutable_result(size_t idx) override {
     ailego_assert_with(idx < results_.size(), "invalid idx");
     return &results_[idx];
   }
 
   //! Retrieve search group result with index
-  virtual const IndexGroupDocumentList &group_result(void) const override {
+  const IndexGroupDocumentList &group_result(void) const override {
     return group_results_[0];
   }
 
   //! Retrieve search group result with index
-  virtual const IndexGroupDocumentList &group_result(
-      size_t idx) const override {
+  const IndexGroupDocumentList &group_result(size_t idx) const override {
     return group_results_[idx];
   }
 
-  virtual IndexGroupDocumentList *mutable_group_result(void) override {
+  IndexGroupDocumentList *mutable_group_result(void) override {
     return &group_results_[0];
   }
 
-  virtual IndexGroupDocumentList *mutable_group_result(size_t idx) override {
+  IndexGroupDocumentList *mutable_group_result(size_t idx) override {
     return &group_results_[idx];
   }
 
-  virtual uint32_t magic(void) const override {
+  uint32_t magic(void) const override {
     return magic_;
   }
 
@@ -111,17 +110,17 @@ class DiskAnnContext : public IndexContext,
   }
 
   //! Set mode of debug
-  virtual void set_debug_mode(bool enable) override {
+  void set_debug_mode(bool enable) override {
     debug_mode_ = enable;
   }
 
   //! Retrieve mode of debug
-  virtual bool debug_mode(void) const override {
+  bool debug_mode(void) const override {
     return debug_mode_;
   }
 
   //! Retrieve string of debug
-  virtual std::string debug_string(void) const override {
+  std::string debug_string(void) const override {
     return std::string("");
   }
 
diff --git a/src/core/algorithm/diskann/diskann_reducer.h b/src/core/algorithm/diskann/diskann_reducer.h
index b912ea1..60e4029 100644
--- a/src/core/algorithm/diskann/diskann_reducer.h
+++ b/src/core/algorithm/diskann/diskann_reducer.h
@@ -32,22 +32,22 @@ class DiskAnnReducer : public IndexReducer {
 
  protected:
   //! Initialize Reducer
-  virtual int init(const ailego::Params &params) override;
+  int init(const ailego::Params &params) override;
 
   //! Cleanup Reducer
-  virtual int cleanup(void) override;
+  int cleanup(void) override;
 
   //! Feed indexes from containers
-  // virtual int feed(IndexStorage::Pointer container) override;
+  // int feed(IndexStorage::Pointer container) override;
 
   //! Reduce operator (with filter)
-  virtual int reduce(const IndexFilter &filter) override;
+  int reduce(const IndexFilter &filter) override;
 
   //! Dump index by dumper
-  virtual int dump(const IndexDumper::Pointer &dumper) override;
+  int dump(const IndexDumper::Pointer &dumper) override;
 
   //! Retrieve statistics
-  virtual const Stats &stats(void) const override {
+  const Stats &stats(void) const override {
     return stats_;
   }
 
diff --git a/src/core/algorithm/diskann/diskann_searcher_entity.h b/src/core/algorithm/diskann/diskann_searcher_entity.h
index 68ab498..953d111 100644
--- a/src/core/algorithm/diskann/diskann_searcher_entity.h
+++ b/src/core/algorithm/diskann/diskann_searcher_entity.h
@@ -32,7 +32,7 @@ class DiskAnnSearcherEntity : public DiskAnnEntity {
   virtual ~DiskAnnSearcherEntity() = default;
 
  public:
-  virtual const DiskAnnEntity::Pointer clone() const override;
+  const DiskAnnEntity::Pointer clone() const override;
 
   int load(const IndexMeta &meta, IndexStorage::Pointer storage);
   int load_pq_segment();
diff --git a/src/core/algorithm/diskann/diskann_streamer.h b/src/core/algorithm/diskann/diskann_streamer.h
index 8d731f3..ddb159a 100644
--- a/src/core/algorithm/diskann/diskann_streamer.h
+++ b/src/core/algorithm/diskann/diskann_streamer.h
@@ -130,11 +130,11 @@ class DiskAnnStreamer : public IndexStreamer {
     return meta_;
   }
 
-  virtual int flush(uint64_t /*check_point*/) override {
+  int flush(uint64_t /*check_point*/) override {
     return 0;
   }
 
-  virtual int close(void) override {
+  int close(void) override {
     return this->unload();
   }
 
diff --git a/src/include/zvec/core/interface/index.h b/src/include/zvec/core/interface/index.h
index 3006718..935a656 100644
--- a/src/include/zvec/core/interface/index.h
+++ b/src/include/zvec/core/interface/index.h
@@ -355,11 +355,11 @@ class ZVEC_CORE_API DiskAnnIndex : public Index {
   DiskAnnIndex() = default;
 
  protected:
-  virtual int CreateAndInitStreamer(const BaseIndexParam &param) override;
+  int CreateAndInitStreamer(const BaseIndexParam &param) override;
 
-  virtual int _prepare_for_search(
-      const VectorData &query, const BaseIndexQueryParam::Pointer &search_param,
-      core::IndexContext::Pointer &context) override;
+  int _prepare_for_search(const VectorData &query,
+                          const BaseIndexQueryParam::Pointer &search_param,
+                          core::IndexContext::Pointer &context) override;
 
   int Add(const VectorData &vector, uint32_t doc_id) override;
 
diff --git a/tools/core/vecs_index_holder.h b/tools/core/vecs_index_holder.h
index 4f743fc..b4c199e 100644
--- a/tools/core/vecs_index_holder.h
+++ b/tools/core/vecs_index_holder.h
@@ -66,37 +66,37 @@ class VecsIndexHolder : public IndexProvider {
           stop_(holder.stop_) {}
 
     //! Test if the iterator is valid
-    virtual bool is_valid(void) const override {
+    bool is_valid(void) const override {
       return !stop_ && cursor_ < vecs_reader_.num_vecs();
     }
 
     //! Retrieve primary key
-    virtual uint64_t key(void) const override {
+    uint64_t key(void) const override {
       return vecs_reader_.get_key(cursor_);
     }
 
     //! Retrieve pointer of data
-    virtual const void *data() const override {
+    const void *data() const override {
       return vecs_reader_.get_vector(cursor_);
     }
 
     //! Retrieve primary key
-    virtual uint32_t sparse_count() const override {
+    uint32_t sparse_count() const override {
       return vecs_reader_.get_sparse_count(cursor_);
     }
 
     //! Retrieve primary key
-    virtual const uint32_t *sparse_indices() const override {
+    const uint32_t *sparse_indices() const override {
       return vecs_reader_.get_sparse_indices(cursor_);
     }
 
     //! Retrieve primary key
-    virtual const void *sparse_data() const override {
+    const void *sparse_data() const override {
       return vecs_reader_.get_sparse_data(cursor_);
     }
 
     //! Next iterator
-    virtual void next(void) override {
+    void next(void) override {
       ++cursor_;
     }
 
@@ -111,14 +111,14 @@ class VecsIndexHolder : public IndexProvider {
     const bool &stop_;
   };
 
-  virtual IndexHolder::Iterator::Pointer create_iterator(void) override {
+  IndexHolder::Iterator::Pointer create_iterator(void) override {
     // make sure iter has value whenn create_iterator finished
     IndexHolder::Iterator::Pointer iter(
         new VecsIndexHolder::Iterator(*this, start_cursor_));
     return iter;
   }
 
-  virtual IndexHybridHolder::Iterator::Pointer create_hybrid_iterator(void) {
+  IndexHybridHolder::Iterator::Pointer create_hybrid_iterator(void) {
     // make sure iter has value whenn create_iterator finished
     IndexHybridHolder::Iterator::Pointer iter(
         new VecsIndexHolder::Iterator(*this, start_cursor_));
@@ -126,29 +126,29 @@ class VecsIndexHolder : public IndexProvider {
   }
 
   //! Retrieve count of elements in holder
-  virtual size_t count(void) const override {
+  size_t count(void) const override {
     return max_doc_count_ != 0
                ? std::min(max_doc_count_, vecs_reader_.num_vecs())
                : vecs_reader_.num_vecs();
   }
 
   //! Retrieve dimension
-  virtual size_t dimension(void) const override {
+  size_t dimension(void) const override {
     return vecs_reader_.index_meta().dimension();
   }
 
   //! Retrieve type information
-  virtual IndexMeta::DataType data_type(void) const override {
+  IndexMeta::DataType data_type(void) const override {
     return vecs_reader_.index_meta().data_type();
   }
 
   //! Retrieve element size in bytes
-  virtual size_t element_size(void) const override {
+  size_t element_size(void) const override {
     return vecs_reader_.index_meta().element_size();
   }
 
   //! Retrieve if it can multi-pass
-  virtual bool multipass(void) const override {
+  bool multipass(void) const override {
     return true;
   }
 
@@ -227,8 +227,8 @@ class VecsIndexHolder : public IndexProvider {
   }
 
   //! Retrieve a vector using a primary key
-  virtual int get_vector(const uint64_t key,
-                         IndexStorage::MemoryBlock &block) const override {
+  int get_vector(const uint64_t key,
+                 IndexStorage::MemoryBlock &block) const override {
     const void *vector = get_vector(key);
     if (vector == nullptr) {
       return IndexError_NoExist;
@@ -238,7 +238,7 @@ class VecsIndexHolder : public IndexProvider {
   }
 
   //! Retrieve the owner class
-  virtual const std::string &owner_class(void) const override {
+  const std::string &owner_class(void) const override {
     static std::string owner_class_name = "VecsIndexHolder";
     return owner_class_name;
   }
@@ -298,32 +298,32 @@ class VecsIndexSparseHolder : public IndexSparseHolder {
           stop_(holder.stop_) {}
 
     //! Test if the iterator is valid
-    virtual bool is_valid(void) const override {
+    bool is_valid(void) const override {
       return !stop_ && cursor_ < vecs_reader_.num_vecs();
     }
 
     //! Retrieve primary key
-    virtual uint64_t key(void) const override {
+    uint64_t key(void) const override {
       return vecs_reader_.get_key(cursor_);
     }
 
     //! Retrieve primary key
-    virtual uint32_t sparse_count() const override {
+    uint32_t sparse_count() const override {
       return vecs_reader_.get_sparse_count(cursor_);
     }
 
     //! Retrieve primary key
-    virtual const uint32_t *sparse_indices() const override {
+    const uint32_t *sparse_indices() const override {
       return vecs_reader_.get_sparse_indices(cursor_);
     }
 
     //! Retrieve primary key
-    virtual const void *sparse_data() const override {
+    const void *sparse_data() const override {
       return vecs_reader_.get_sparse_data(cursor_);
     }
 
     //! Next iterator
-    virtual void next(void) override {
+    void next(void) override {
       ++cursor_;
     }
 
@@ -338,7 +338,7 @@ class VecsIndexSparseHolder : public IndexSparseHolder {
     const bool &stop_;
   };
 
-  virtual IndexSparseHolder::Iterator::Pointer create_iterator(void) override {
+  IndexSparseHolder::Iterator::Pointer create_iterator(void) override {
     // make sure iter has value whenn create_iterator finished
     IndexSparseHolder::Iterator::Pointer iter(
         new VecsIndexSparseHolder::Iterator(*this, start_cursor_));
@@ -346,19 +346,19 @@ class VecsIndexSparseHolder : public IndexSparseHolder {
   }
 
   //! Retrieve count of elements in holder
-  virtual size_t count(void) const override {
+  size_t count(void) const override {
     return max_doc_count_ != 0
                ? std::min(max_doc_count_, vecs_reader_.num_vecs())
                : vecs_reader_.num_vecs();
   }
 
   //! Retrieve type information
-  virtual IndexMeta::DataType data_type(void) const override {
+  IndexMeta::DataType data_type(void) const override {
     return vecs_reader_.index_meta().data_type();
   }
 
   //! Retrieve if it can multi-pass
-  virtual bool multipass(void) const override {
+  bool multipass(void) const override {
     return true;
   }