diff --git a/cpp/src/db/db.h b/cpp/src/db/db.h
index c14822b041..74dfe93edf 100644
--- a/cpp/src/db/db.h
+++ b/cpp/src/db/db.h
@@ -19,12 +19,12 @@ public:
 
     virtual Status add_group(const GroupOptions& options_,
             const std::string& group_id_,
-            GroupSchema& group_info_) = 0;
-    virtual Status get_group(const std::string& group_id_, GroupSchema& group_info_) = 0;
+            meta::GroupSchema& group_info_) = 0;
+    virtual Status get_group(const std::string& group_id_, meta::GroupSchema& group_info_) = 0;
     virtual Status has_group(const std::string& group_id_, bool& has_or_not_) = 0;
     virtual Status get_group_files(const std::string& group_id_,
                                    const int date_delta_,
-                                   GroupFilesSchema& group_files_info_) = 0;
+                                   meta::GroupFilesSchema& group_files_info_) = 0;
 
     virtual Status add_vectors(const std::string& group_id_,
             size_t n, const float* vectors, IDNumbers& vector_ids_) = 0;
diff --git a/cpp/src/db/db_impl.cpp b/cpp/src/db/db_impl.cpp
index 87c83e7027..723b80cb4a 100644
--- a/cpp/src/db/db_impl.cpp
+++ b/cpp/src/db/db_impl.cpp
@@ -1,6 +1,10 @@
 #include <assert.h>
 #include <chrono>
 #include <thread>
+#include <iostream>
+#include <faiss/IndexFlat.h>
+#include <faiss/MetaIndexes.h>
+#include <faiss/index_io.h>
 #include "db_impl.h"
 #include "db_meta_impl.h"
 #include "env.h"
@@ -15,21 +19,21 @@ DBImpl::DBImpl(const Options& options_, const std::string& name_)
       _options(options_),
       _bg_compaction_scheduled(false),
       _shutting_down(false),
-      _pMeta(new DBMetaImpl(*(_options.pMetaOptions))),
+      _pMeta(new meta::DBMetaImpl(*(_options.pMetaOptions))),
       _pMemMgr(new MemManager(_pMeta)) {
     start_timer_task(options_.memory_sync_interval);
 }
 
 Status DBImpl::add_group(const GroupOptions& options,
         const std::string& group_id,
-        GroupSchema& group_info) {
+        meta::GroupSchema& group_info) {
     assert((!options.has_id) ||
             (options.has_id && ("" != group_id)));
 
     return _pMeta->add_group(options, group_id, group_info);
 }
 
-Status DBImpl::get_group(const std::string& group_id_, GroupSchema& group_info_) {
+Status DBImpl::get_group(const std::string& group_id_, meta::GroupSchema& group_info_) {
     return _pMeta->get_group(group_id_, group_info_);
 }
 
@@ -39,7 +43,7 @@ Status DBImpl::has_group(const std::string& group_id_, bool& has_or_not_) {
 
 Status DBImpl::get_group_files(const std::string& group_id,
                                const int date_delta,
-                               GroupFilesSchema& group_files_info) {
+                               meta::GroupFilesSchema& group_files_info) {
     return _pMeta->get_group_files(group_id, date_delta, group_files_info);
 
 }
@@ -99,8 +103,64 @@ void DBImpl::background_call() {
     _bg_work_finish_signal.notify_all();
 }
 
+
+Status DBImpl::merge_files(const std::string& group_id, const meta::DateT& date,
+        const meta::GroupFilesSchema& files) {
+    meta::GroupFileSchema group_file;
+    Status status = _pMeta->add_group_file(group_id, date, group_file);
+    if (!status.ok()) {
+        return status;
+    }
+
+    faiss::IndexFlat innerIndex(group_file.dimension);
+    faiss::IndexIDMap index(&innerIndex);
+
+    meta::GroupFilesSchema updated;
+
+    for (auto& file : files) {
+        auto file_index = dynamic_cast<faiss::IndexIDMap*>(faiss::read_index(file.location.c_str()));
+        index.add_with_ids(file_index->ntotal, dynamic_cast<faiss::IndexFlat*>(file_index->index)->xb.data(),
+                file_index->id_map.data());
+        auto file_schema = file;
+        file_schema.file_type = meta::GroupFileSchema::TO_DELETE;
+        updated.push_back(file_schema);
+    }
+
+    faiss::write_index(&index, group_file.location.c_str());
+    group_file.file_type = meta::GroupFileSchema::RAW;
+    updated.push_back(group_file);
+    status = _pMeta->update_files(updated);
+
+    return status;
+}
+
+Status DBImpl::background_merge_files(const std::string& group_id) {
+    meta::DatePartionedGroupFilesSchema raw_files;
+    /* auto status = _pMeta->get_small_raw_files(group_id, raw_files); */
+    /* if (!status.ok()) { */
+    /*     _bg_error = status; */
+    /*     return status; */
+    /* } */
+
+    if (raw_files.size() == 0) {
+        return Status::OK();
+    }
+
+    for (auto& kv : raw_files) {
+        merge_files(group_id, kv.first, kv.second);
+    }
+}
+
 void DBImpl::background_compaction() {
-    _pMemMgr->serialize();
+    std::vector<std::string> group_ids;
+    _pMemMgr->serialize(group_ids);
+    for (auto group_id : group_ids) {
+        std::cout << __func__ << " group_id=" << group_id << std::endl;
+    }
+
+    if (group_ids.size() > 0) {
+
+    }
 }
 
 DBImpl::~DBImpl() {
diff --git a/cpp/src/db/db_impl.h b/cpp/src/db/db_impl.h
index b8e45f8006..18c6b154d1 100644
--- a/cpp/src/db/db_impl.h
+++ b/cpp/src/db/db_impl.h
@@ -14,19 +14,23 @@ namespace engine {
 
 class Env;
 
+namespace meta {
+    class Meta;
+}
+
 class DBImpl : public DB {
 public:
     DBImpl(const Options& options_, const std::string& name_);
 
     virtual Status add_group(const GroupOptions& options_,
             const std::string& group_id_,
-            GroupSchema& group_info_) override;
-    virtual Status get_group(const std::string& group_id_, GroupSchema& group_info_) override;
+            meta::GroupSchema& group_info_) override;
+    virtual Status get_group(const std::string& group_id_, meta::GroupSchema& group_info_) override;
     virtual Status has_group(const std::string& group_id_, bool& has_or_not_) override;
 
     virtual Status get_group_files(const std::string& group_id_,
                                    const int date_delta_,
-                                   GroupFilesSchema& group_files_info_) override;
+                                   meta::GroupFilesSchema& group_files_info_) override;
 
     virtual Status add_vectors(const std::string& group_id_,
             size_t n, const float* vectors, IDNumbers& vector_ids_) override;
@@ -37,6 +41,10 @@ public:
     virtual ~DBImpl();
 
 private:
+    Status merge_files(const std::string& group_id,
+            const meta::DateT& date,
+            const meta::GroupFilesSchema& files);
+    Status background_merge_files(const std::string& group_id);
 
     void try_schedule_compaction();
     void start_timer_task(int interval_);
@@ -56,7 +64,7 @@ private:
     Status _bg_error;
     std::atomic<bool> _shutting_down;
 
-    std::shared_ptr<Meta> _pMeta;
+    std::shared_ptr<meta::Meta> _pMeta;
     std::shared_ptr<MemManager> _pMemMgr;
 
 }; // DBImpl
diff --git a/cpp/src/db/db_meta.cpp b/cpp/src/db/db_meta.cpp
index 9274b8258e..2ac0995962 100644
--- a/cpp/src/db/db_meta.cpp
+++ b/cpp/src/db/db_meta.cpp
@@ -1,10 +1,21 @@
+#include <ctime>
 #include "db_meta.h"
 
 namespace zilliz {
 namespace vecwise {
 namespace engine {
+namespace meta {
 
+DateT Meta::GetDate(const std::time_t& t) {
+    tm *ltm = std::localtime(&t);
+    return ltm->tm_year*10000 + ltm->tm_mon*100 + ltm->tm_mday;
+}
 
+DateT Meta::GetDate() {
+    return GetDate(std::time(nullptr));
+}
+
+} // namespace meta
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
diff --git a/cpp/src/db/db_meta.h b/cpp/src/db/db_meta.h
index 1eae4b95a6..22ab911fd3 100644
--- a/cpp/src/db/db_meta.h
+++ b/cpp/src/db/db_meta.h
@@ -3,12 +3,17 @@
 #include <string>
 #include <cstddef>
 #include <vector>
+#include <map>
+#include <ctime>
 #include "options.h"
 #include "status.h"
 
 namespace zilliz {
 namespace vecwise {
 namespace engine {
+namespace meta {
+
+typedef int DateT;
 
 struct GroupSchema {
     size_t id;
@@ -22,19 +27,24 @@ struct GroupSchema {
 
 struct GroupFileSchema {
     typedef enum {
+        NEW,
         RAW,
-        INDEX
+        INDEX,
+        TO_DELETE,
     } FILE_TYPE;
 
     size_t id;
     std::string group_id;
     std::string file_id;
-    int files_type = RAW;
+    int file_type = NEW;
     size_t rows;
+    DateT date;
+    uint16_t dimension;
     std::string location = "";
 }; // GroupFileSchema
 
 typedef std::vector<GroupFileSchema> GroupFilesSchema;
+typedef std::map<DateT, GroupFilesSchema> DatePartionedGroupFilesSchema;
 
 
 class Meta {
@@ -47,6 +57,9 @@ public:
 
     virtual Status add_group_file(const std::string& group_id_,
                                   GroupFileSchema& group_file_info_) = 0;
+    virtual Status add_group_file(const std::string& group_id,
+                                  DateT date,
+                                  GroupFileSchema& group_file_info) = 0;
     virtual Status has_group_file(const std::string& group_id_,
                                   const std::string& file_id_,
                                   bool& has_or_not_) = 0;
@@ -59,8 +72,14 @@ public:
                                    const int date_delta_,
                                    GroupFilesSchema& group_files_info_) = 0;
 
+    virtual Status update_files(const GroupFilesSchema& files) = 0;
+
+    static DateT GetDate(const std::time_t& t);
+    static DateT GetDate();
+
 }; // MetaData
 
+} // namespace meta
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
diff --git a/cpp/src/db/db_meta_impl.cpp b/cpp/src/db/db_meta_impl.cpp
index 7ab9f65000..1f8c4a94ce 100644
--- a/cpp/src/db/db_meta_impl.cpp
+++ b/cpp/src/db/db_meta_impl.cpp
@@ -6,6 +6,7 @@
 namespace zilliz {
 namespace vecwise {
 namespace engine {
+namespace meta {
 
 DBMetaImpl::DBMetaImpl(const MetaOptions& options_)
     : _options(static_cast<const DBMetaOptions&>(options_)) {
@@ -26,12 +27,6 @@ Status DBMetaImpl::add_group(const GroupOptions& options_,
 
 Status DBMetaImpl::get_group(const std::string& group_id_, GroupSchema& group_info_) {
     //PXU TODO
-    std::stringstream ss;
-    SimpleIDGenerator g;
-    ss.str("");
-    ss << "/tmp/test/" << g.getNextIDNumber() << ".log";
-    group_info_.dimension = 64;
-    group_info_.next_file_location = ss.str();
     return Status::OK();
 }
 
@@ -40,9 +35,24 @@ Status DBMetaImpl::has_group(const std::string& group_id_, bool& has_or_not_) {
     return Status::OK();
 }
 
-Status DBMetaImpl::add_group_file(const std::string& group_id_,
-                              GroupFileSchema& group_file_info_) {
+Status DBMetaImpl::add_group_file(const std::string& group_id,
+                              GroupFileSchema& group_file_info) {
+    return add_group_file(group_id, Meta::GetDate(), group_file_info);
+}
+
+Status DBMetaImpl::add_group_file(const std::string& group_id,
+                              DateT date,
+                              GroupFileSchema& group_file_info) {
     //PXU TODO
+    std::stringstream ss;
+    SimpleIDGenerator g;
+    ss << "/tmp/test/" << date
+                       << "/" << g.getNextIDNumber()
+                       << ".log";
+    group_file_info.group_id = "1";
+    group_file_info.dimension = 64;
+    group_file_info.location = ss.str();
+    group_file_info.date = date;
     return Status::OK();
 }
 
@@ -72,6 +82,12 @@ Status DBMetaImpl::update_group_file(const GroupFileSchema& group_file_) {
     return Status::OK();
 }
 
+Status DBMetaImpl::update_files(const GroupFilesSchema& files) {
+    //PXU TODO
+    return Status::OK();
+}
+
+} // namespace meta
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
diff --git a/cpp/src/db/db_meta_impl.h b/cpp/src/db/db_meta_impl.h
index f8602c1635..06e04902ce 100644
--- a/cpp/src/db/db_meta_impl.h
+++ b/cpp/src/db/db_meta_impl.h
@@ -7,6 +7,7 @@
 namespace zilliz {
 namespace vecwise {
 namespace engine {
+namespace meta {
 
 class DBMetaImpl : public Meta {
 public:
@@ -18,6 +19,9 @@ public:
     virtual Status get_group(const std::string& group_id_, GroupSchema& group_info_) override;
     virtual Status has_group(const std::string& group_id_, bool& has_or_not_) override;
 
+    virtual Status add_group_file(const std::string& group_id,
+                                  DateT date,
+                                  GroupFileSchema& group_file_info) override;
     virtual Status add_group_file(const std::string& group_id_,
                                   GroupFileSchema& group_file_info_) override;
     virtual Status has_group_file(const std::string& group_id_,
@@ -32,6 +36,8 @@ public:
                                    const int date_delta_,
                                    GroupFilesSchema& group_files_info_) override;
 
+    virtual Status update_files(const GroupFilesSchema& files) override;
+
 private:
 
     Status initialize();
@@ -40,6 +46,7 @@ private:
 
 }; // DBMetaImpl
 
+} // namespace meta
 } // namespace engine
 } // namespace vecwise
 } // namespace zilliz
diff --git a/cpp/src/db/memvectors.cpp b/cpp/src/db/memvectors.cpp
index 2bafe3a9de..384e69be3f 100644
--- a/cpp/src/db/memvectors.cpp
+++ b/cpp/src/db/memvectors.cpp
@@ -13,10 +13,12 @@ namespace zilliz {
 namespace vecwise {
 namespace engine {
 
-MemVectors::MemVectors(size_t dimension_, const std::string& file_location_) :
-    _file_location(file_location_),
+MemVectors::MemVectors(const std::string& group_id,
+        size_t dimension, const std::string& file_location) :
+    group_id_(group_id),
+    _file_location(file_location),
     _pIdGenerator(new SimpleIDGenerator()),
-    _dimension(dimension_),
+    _dimension(dimension),
     _pInnerIndex(new faiss::IndexFlat(_dimension)),
     _pIdMapIndex(new faiss::IndexIDMap(_pInnerIndex)) {
 }
@@ -37,13 +39,15 @@ size_t MemVectors::approximate_size() const {
     return total() * _dimension;
 }
 
-void MemVectors::serialize() {
+Status MemVectors::serialize(std::string& group_id) {
     /* std::stringstream ss; */
     /* ss << "/tmp/test/" << _pIdGenerator->getNextIDNumber(); */
     /* faiss::write_index(_pIdMapIndex, ss.str().c_str()); */
     /* std::cout << _pIdMapIndex->ntotal << std::endl; */
     /* std::cout << _file_location << std::endl; */
     faiss::write_index(_pIdMapIndex, _file_location.c_str());
+    group_id = group_id_;
+    return Status::OK();
 }
 
 MemVectors::~MemVectors() {
@@ -71,14 +75,15 @@ VectorsPtr MemManager::get_mem_by_group(const std::string& group_id) {
         return memIt->second;
     }
 
-    GroupSchema group_info;
-    Status status = _pMeta->get_group(group_id, group_info);
+    meta::GroupFileSchema group_file;
+    auto status = _pMeta->add_group_file(group_id, group_file);
     if (!status.ok()) {
         return nullptr;
     }
 
-    _memMap[group_id] = std::shared_ptr<MemVectors>(new MemVectors(group_info.dimension,
-                group_info.next_file_location));
+    _memMap[group_id] = std::shared_ptr<MemVectors>(new MemVectors(group_file.group_id,
+                group_file.dimension,
+                group_file.location));
     return _memMap[group_id];
 }
 
@@ -126,10 +131,13 @@ Status MemManager::mark_memory_as_immutable() {
 /*     return false; */
 /* } */
 
-Status MemManager::serialize() {
+Status MemManager::serialize(std::vector<std::string>& group_ids) {
     mark_memory_as_immutable();
+    std::string group_id;
+    group_ids.clear();
     for (auto& mem : _immMems) {
-        mem->serialize();
+        mem->serialize(group_id);
+        group_ids.push_back(group_id);
     }
     _immMems.clear();
     return Status::OK();
diff --git a/cpp/src/db/memvectors.h b/cpp/src/db/memvectors.h
index f9a0bba1f2..5a6df87eae 100644
--- a/cpp/src/db/memvectors.h
+++ b/cpp/src/db/memvectors.h
@@ -19,9 +19,15 @@ namespace zilliz {
 namespace vecwise {
 namespace engine {
 
+namespace meta {
+    class Meta;
+}
+
 class MemVectors {
 public:
-    explicit MemVectors(size_t dimension_, const std::string& file_location_);
+    explicit MemVectors(const std::string& group_id,
+            size_t dimension,
+            const std::string& file_location);
 
     void add(size_t n_, const float* vectors_, IDNumbers& vector_ids_);
 
@@ -29,7 +35,7 @@ public:
 
     size_t approximate_size() const;
 
-    void serialize();
+    Status serialize(std::string& group_id);
 
     ~MemVectors();
 
@@ -40,6 +46,7 @@ private:
     MemVectors(const MemVectors&) = delete;
     MemVectors& operator=(const MemVectors&) = delete;
 
+    std::string group_id_;
     const std::string _file_location;
     IDGenerator* _pIdGenerator;
     size_t _dimension;
@@ -49,12 +56,11 @@ private:
 }; // MemVectors
 
 
-class Meta;
 typedef std::shared_ptr<MemVectors> VectorsPtr;
 
 class MemManager {
 public:
-    MemManager(const std::shared_ptr<Meta>& meta_)
+    MemManager(const std::shared_ptr<meta::Meta>& meta_)
         : _pMeta(meta_) /*_last_compact_time(std::time(nullptr))*/ {}
 
     VectorsPtr get_mem_by_group(const std::string& group_id_);
@@ -62,7 +68,7 @@ public:
     Status add_vectors(const std::string& group_id_,
             size_t n_, const float* vectors_, IDNumbers& vector_ids_);
 
-    Status serialize();
+    Status serialize(std::vector<std::string>& group_ids);
 
 private:
     Status add_vectors_no_lock(const std::string& group_id_,
@@ -73,7 +79,7 @@ private:
     typedef std::vector<VectorsPtr> ImmMemPool;
     MemMap _memMap;
     ImmMemPool _immMems;
-    std::shared_ptr<Meta> _pMeta;
+    std::shared_ptr<meta::Meta> _pMeta;
     /* std::time_t _last_compact_time; */
     std::mutex _mutex;
 }; // MemManager