diff --git a/cpp/src/db/memvectors.cpp b/cpp/src/db/memvectors.cpp
index f76589a628f60f62adaca9c0e95b3fd449d5da62..abc6b67dfd8066666eab2b4e24948073f57eb9d9 100644
--- a/cpp/src/db/memvectors.cpp
+++ b/cpp/src/db/memvectors.cpp
@@ -1,19 +1,21 @@
-#include <IndexFlat.h>
-#include <MetaIndexes.h>
-#include <index_io.h>
+#include <faiss/IndexFlat.h>
+#include <faiss/MetaIndexes.h>
+#include <faiss/index_io.h>
 
 #include "memvectors.h"
 #include "db_meta.h"
 
 
-namespace vecengine {
+namespace zilliz {
+namespace vecwise {
+namespace engine {
 
 MemVectors::MemVectors(size_t dimension_, const std::string& file_location_) :
-    _file_location(file_location_),
+    _file_location(file_location_.c_str()),
     _pIdGenerator(new SimpleIDGenerator()),
     _dimension(dimension_),
     _pInnerIndex(new faiss::IndexFlat(_dimension)),
-    _pIdMapIndex = new faiss::IndexIDMap(_pInnerIndex) {
+    _pIdMapIndex(new faiss::IndexIDMap(_pInnerIndex)) {
 }
 
 void MemVectors::add(size_t n_, const float* vectors_, IDNumbers& vector_ids_) {
@@ -52,14 +54,14 @@ MemVectors::~MemVectors() {
  * MemManager
  */
 
-VectorsPtr MemManager::get_mem_by_group(const std::string& group_id_) {
-    auto memIt = _memMap.find(group_id_);
-    if memIt != _memMap.end() {
-        return &(memIt->second);
+VectorsPtr MemManager::get_mem_by_group(const std::string& group_id) {
+    auto memIt = _memMap.find(group_id);
+    if (memIt != _memMap.end()) {
+        return memIt->second;
     }
 
     GroupSchema group_info;
-    Status status = _pMeta->get_group(group_id_, group_info);
+    Status status = _pMeta->get_group(group_id, group_info);
     if (!status.ok()) {
         return nullptr;
     }
@@ -76,15 +78,17 @@ Status MemManager::add_vectors(const std::string& group_id_,
     return add_vectors_no_lock(group_id_, n_, vectors_, vector_ids_);
 }
 
-Status MemManager::add_vectors_no_lock(const std::string& group_id_,
+Status MemManager::add_vectors_no_lock(const std::string& group_id,
         size_t n,
         const float* vectors,
-        IDNumbers& vector_ids_) {
-    auto mem = get_mem_by_group(group_id_);
+        IDNumbers& vector_ids) {
+    auto mem = get_mem_by_group(group_id);
     if (mem == nullptr) {
-        return Status::NotFound("Group " + group_id_ " not found!");
+        return Status::NotFound("Group " + group_id + " not found!");
     }
-    return mem->add(n, vectors, vector_ids_);
+    mem->add(n, vectors, vector_ids);
+
+    return Status::OK();
 }
 
 Status MemManager::mark_memory_as_immutable() {
@@ -111,11 +115,13 @@ Status MemManager::mark_memory_as_immutable() {
 Status MemManager::serialize() {
     mark_memory_as_immutable();
     for (auto& mem : _immMems) {
-        mem->serialize()
+        mem->serialize();
     }
     _immMems.clear();
     /* _last_compact_time = std::time(nullptr); */
 }
 
 
-} // namespace vecengine
+} // namespace engine
+} // namespace vecwise
+} // namespace zilliz
diff --git a/cpp/src/db/memvectors.h b/cpp/src/db/memvectors.h
index 034d039010be0ab5771fdc7ae1607d4a264e25f9..f60f37af88651e67c2732b0497c58e9bcf8442d3 100644
--- a/cpp/src/db/memvectors.h
+++ b/cpp/src/db/memvectors.h
@@ -4,6 +4,8 @@
 #include <map>
 #include <string>
 #include <ctime>
+#include <memory>
+#include <mutex>
 #include "id_generators.h"
 #include "status.h"
 
@@ -21,7 +23,7 @@ class MemVectors {
 public:
     explicit MemVectors(size_t dimension_, const std::string& file_location_);
 
-    IDNumbers&& add(size_t n, const float* vectors);
+    void add(size_t n_, const float* vectors_, IDNumbers& vector_ids_);
 
     size_t total() const;
 
@@ -32,7 +34,7 @@ public:
     ~MemVectors();
 
 private:
-    std::string _file_location;
+    const char* _file_location;
     IDGenerator* _pIdGenerator;
     size_t _dimension;
     faiss::Index* _pInnerIndex;
@@ -42,10 +44,10 @@ private:
 
 
 class Meta;
+typedef std::shared_ptr<MemVectors> VectorsPtr;
 
 class MemManager {
 public:
-    typedef std::shared_ptr<MemVectors> VectorsPtr;
     MemManager(const std::shared_ptr<Meta>& meta_)
         : _pMeta(meta_), _last_compact_time(std::time(nullptr)) {}
 
@@ -59,6 +61,7 @@ public:
 private:
     Status add_vectors_no_lock(const std::string& group_id_,
             size_t n_, const float* vectors_, IDNumbers& vector_ids_);
+    Status mark_memory_as_immutable();
 
     typedef std::map<std::string, VectorsPtr> MemMap;
     typedef std::vector<VectorsPtr> ImmMemPool;
diff --git a/cpp/src/db/options.cpp b/cpp/src/db/options.cpp
index dd28cdb7ddab78977463552a9d3273a032eb1c6e..be572c232f62d87af019d2e098c9d49c68ab0421 100644
--- a/cpp/src/db/options.cpp
+++ b/cpp/src/db/options.cpp
@@ -1,4 +1,5 @@
 #include "options.h"
+#include "env.h"
 
 namespace zilliz {
 namespace vecwise {
diff --git a/cpp/src/db/options.h b/cpp/src/db/options.h
index aefd094edfc5e584ebb152bb45a44dabace39361..807bae38b256830a1f8a8e9cb132b849d76a562d 100644
--- a/cpp/src/db/options.h
+++ b/cpp/src/db/options.h
@@ -1,5 +1,4 @@
-#ifndef VECENGINE_OPTIONS_H_
-#define VECENGINE_OPTIONS_H_
+#pragma once
 
 #include <string>
 #include <memory>
@@ -12,6 +11,7 @@ class MetaOptions;
 class Env;
 
 struct Options {
+    Options();
     uint16_t  memory_sync_interval = 10;
     uint16_t  raw_file_merge_trigger_number = 100;
     size_t  raw_to_index_trigger_size = 100000;
@@ -39,5 +39,3 @@ struct DBMetaOptions : public MetaOptions {
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
-
-#endif // VECENGINE_OPTIONS_H_
diff --git a/cpp/src/db/types.h b/cpp/src/db/types.h
index 7fd33a0787ff74833d9ef03b9a22aa4f19d9d0cf..c9ed274defe7537baf471a42d43a37fa674dc1d6 100644
--- a/cpp/src/db/types.h
+++ b/cpp/src/db/types.h
@@ -6,7 +6,7 @@ namespace zilliz {
 namespace vecwise {
 namespace engine {
 
-typedef uint64_t IDNumber;
+typedef long IDNumber;
 typedef IDNumber* IDNumberPtr;
 typedef std::vector<IDNumber> IDNumbers;