diff --git a/core/unittest/db/test_db.cpp b/core/unittest/db/test_db.cpp
index 2b9db83c4e..1e640fdd2c 100644
--- a/core/unittest/db/test_db.cpp
+++ b/core/unittest/db/test_db.cpp
@@ -250,13 +250,13 @@ TEST_F(DBTest, DB_TEST) {
     {
         auto options = GetOptions();
         options.meta_.backend_uri_ = "dummy";
-        ASSERT_ANY_THROW(milvus::engine::DBFactory::Build(options));
+        ASSERT_ANY_THROW(BuildDB(options));
 
         options.meta_.backend_uri_ = "mysql://root:123456@127.0.0.1:3306/test";
-        ASSERT_ANY_THROW(milvus::engine::DBFactory::Build(options));
+        ASSERT_ANY_THROW(BuildDB(options));
 
         options.meta_.backend_uri_ = "dummy://root:123456@127.0.0.1:3306/test";
-        ASSERT_ANY_THROW(milvus::engine::DBFactory::Build(options));
+        ASSERT_ANY_THROW(BuildDB(options));
     }
 }
 
@@ -1116,17 +1116,13 @@ TEST_F(DBTestWALRecovery, RECOVERY_WITH_NO_ERROR) {
     milvus::engine::ResultDistances result_distances;
     milvus::engine::VectorsData qxb;
     BuildVectors(qb, 0, qxb);
-    stat = db_->Query(dummy_context_,
-            collection_info.collection_id_, {}, topk, json_params, qxb, result_ids, result_distances);
-    ASSERT_TRUE(stat.ok());
-    ASSERT_NE(result_ids.size() / topk, qb);
 
     fiu_init(0);
     fiu_enable("DBImpl.ExexWalRecord.return", 1, nullptr, 0);
-    db_ = nullptr;
+    db_ = nullptr; // don't use FreeDB(), this case needs keep the meta
     fiu_disable("DBImpl.ExexWalRecord.return");
     auto options = GetOptions();
-    db_ = milvus::engine::DBFactory::Build(options);
+    BuildDB(options);
 
     result_ids.clear();
     result_distances.clear();
@@ -1158,13 +1154,13 @@ TEST_F(DBTestWALRecovery_Error, RECOVERY_WITH_INVALID_LOG_FILE) {
 
     fiu_init(0);
     fiu_enable("DBImpl.ExexWalRecord.return", 1, nullptr, 0);
-    db_ = nullptr;
+    FreeDB();
     fiu_disable("DBImpl.ExexWalRecord.return");
 
     auto options = GetOptions();
     // delete wal log file so that recovery will failed when start db next time.
     boost::filesystem::remove(options.mxlog_path_ + "0.wal");
-    ASSERT_ANY_THROW(db_ = milvus::engine::DBFactory::Build(options));
+    ASSERT_ANY_THROW(BuildDB(options));
 }
 
 TEST_F(DBTest2, FLUSH_NON_EXISTING_COLLECTION) {
@@ -1256,7 +1252,6 @@ TEST_F(DBTest2, GET_VECTOR_BY_ID_INVALID_TEST) {
     fiu_disable("bloom_filter_nullptr");
 }
 
-
 TEST_F(DBTest2, GET_VECTOR_IDS_TEST) {
     milvus::engine::meta::CollectionSchema collection_schema = BuildCollectionSchema();
     auto stat = db_->CreateCollection(collection_schema);
@@ -1316,11 +1311,11 @@ TEST_F(DBTest2, GET_VECTOR_IDS_TEST) {
 TEST_F(DBTest2, INSERT_DUPLICATE_ID) {
     auto options = GetOptions();
     options.wal_enable_ = false;
-    db_ = milvus::engine::DBFactory::Build(options);
+    BuildDB(options);
 
     milvus::engine::meta::CollectionSchema collection_schema = BuildCollectionSchema();
     auto stat = db_->CreateCollection(collection_schema);
-    ASSERT_TRUE(stat.ok()) << " CreateCollection: " << stat.message();
+    ASSERT_TRUE(stat.ok());
 
     uint64_t size = 20;
     milvus::engine::VectorsData vector;
@@ -1331,10 +1326,10 @@ TEST_F(DBTest2, INSERT_DUPLICATE_ID) {
     }
 
     stat = db_->InsertVectors(COLLECTION_NAME, "", vector);
-    ASSERT_TRUE(stat.ok()) << " InsertVectors: " << stat.message();
+    ASSERT_TRUE(stat.ok());
 
     stat = db_->Flush(COLLECTION_NAME);
-    ASSERT_TRUE(stat.ok()) << " Flush: " << stat.message();
+    ASSERT_TRUE(stat.ok());
 }
 
 /*
diff --git a/core/unittest/db/utils.cpp b/core/unittest/db/utils.cpp
index 1cd00dc0fc..9d4da2e4aa 100644
--- a/core/unittest/db/utils.cpp
+++ b/core/unittest/db/utils.cpp
@@ -26,7 +26,6 @@
 #include "db/DBFactory.h"
 #include "db/Options.h"
 
-
 #ifdef MILVUS_GPU_VERSION
 #include "knowhere/index/vector_index/helpers/FaissGpuResourceMgr.h"
 #endif
@@ -255,7 +254,7 @@ DBTest::SetUp() {
 
     auto options = GetOptions();
     options.insert_cache_immediately_ = true;
-    db_ = milvus::engine::DBFactory::Build(options);
+    BuildDB(options);
 
     std::string config_path(options.meta_.path_ + CONFIG_FILE);
     WriteToFile(config_path, CONFIG_STR);
@@ -263,10 +262,7 @@ DBTest::SetUp() {
 
 void
 DBTest::TearDown() {
-    if (db_) {
-        db_->Stop();
-        db_->DropAll();
-    }
+    FreeDB();
 
     milvus::scheduler::JobMgrInst::GetInstance()->Stop();
     milvus::scheduler::SchedInst::GetInstance()->Stop();
@@ -280,6 +276,21 @@ DBTest::TearDown() {
     boost::filesystem::remove_all(options.meta_.path_);
 }
 
+void
+DBTest::BuildDB(const milvus::engine::DBOptions& options) {
+    FreeDB();
+    db_ = milvus::engine::DBFactory::Build(options);
+}
+
+void
+DBTest::FreeDB() {
+    if (db_) {
+        db_->Stop();
+        db_->DropAll();
+        db_ = nullptr;
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 milvus::engine::DBOptions
 DBTest2::GetOptions() {
diff --git a/core/unittest/db/utils.h b/core/unittest/db/utils.h
index 8c4abed4fe..59f63d8e27 100644
--- a/core/unittest/db/utils.h
+++ b/core/unittest/db/utils.h
@@ -72,6 +72,12 @@ class DBTest : public BaseTest {
     SetUp() override;
     void
     TearDown() override;
+
+    void
+    BuildDB(const milvus::engine::DBOptions& options);
+
+    void
+    FreeDB();
 };
 
 /////////////////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/sdk/README.md b/sdk/README.md
index a57c698b90..63106119a2 100644
--- a/sdk/README.md
+++ b/sdk/README.md
@@ -32,7 +32,7 @@ Run C++ example:
 
 ### Create your own C++ client project
 
-Create a folder for the project, and copy C++ SDK header and library files into it.
+- Create a folder for the project, and copy C++ SDK header and library files into it.
 
 ```shell
  # create project folder
@@ -41,15 +41,14 @@ Create a folder for the project, and copy C++ SDK header and library files into
  
  # copy necessary files
  $ cp [Milvus root path]/sdk/cmake_build/libmilvus_sdk.so .
- $ cp [Milvus root path]/sdk/include/MilvusApi.h .
- $ cp [Milvus root path]/sdk/include/Status.h .
+ $ cp -r [Milvus root path]/sdk/include .
 ```
 
-Create file `main.cpp` in the project folder, and copy the following code into it:
+- Create file `main.cpp` in the project folder, and copy the following code into it:
 
 ```c++
-#include "./MilvusApi.h"
-#include "./Status.h"
+#include "./include/MilvusApi.h"
+#include "./include/Status.h"
 
 int main() {
   // connect to milvus server
@@ -64,7 +63,7 @@ int main() {
 }
 ```
 
-Create file `CMakeLists.txt` in the project folder, and copy the following code into it:
+- Create file `CMakeLists.txt` in the project folder, and copy the following code into it:
 
 ```bash
  cmake_minimum_required(VERSION 3.14)
@@ -77,18 +76,20 @@ Create file `CMakeLists.txt` in the project folder, and copy the following code
          pthread)
 ```
 
-Now there are 5 files in your project:
+- Now the file structure of your project:
 
 ```shell
 MyMilvusClient
  |-CMakeLists.txt
  |-main.cpp
  |-libmilvus_sdk.so
- |-MilvusApi.h
- |-Status.h
+ |-include
+     |-MilvusApi.h
+     |-Status.h
+     |-......
 ```
 
-Build the project:
+- Build the project:
 
 ```shell
  $ mkdir cmake_build
@@ -97,8 +98,15 @@ Build the project:
  $ make
 ```
 
-Run your client program:
+- Run your client program:
 
 ```shell
  $ ./milvus_client
 ```
+
+### Troubleshooting
+
+- compile error "cannot find -lz"
+```shell
+ $ apt-get install zlib1g-dev.
+```
\ No newline at end of file