diff --git a/cpp/src/db/DB.h b/cpp/src/db/DB.h
index 0a84ffd7ff..282e762717 100644
--- a/cpp/src/db/DB.h
+++ b/cpp/src/db/DB.h
@@ -33,14 +33,14 @@ public:
     virtual Status InsertVectors(const std::string& table_id_,
             uint64_t n, const float* vectors, IDNumbers& vector_ids_) = 0;
 
-    virtual Status Query(const std::string& table_id, uint64_t k, uint64_t nq,
+    virtual Status Query(const std::string& table_id, uint64_t k, uint64_t nq, uint64_t nprobe,
             const float* vectors, QueryResults& results) = 0;
 
-    virtual Status Query(const std::string& table_id, uint64_t k, uint64_t nq,
+    virtual Status Query(const std::string& table_id, uint64_t k, uint64_t nq, uint64_t nprobe,
             const float* vectors, const meta::DatesT& dates, QueryResults& results) = 0;
 
     virtual Status Query(const std::string& table_id, const std::vector<std::string>& file_ids,
-            uint64_t k, uint64_t nq, const float* vectors,
+            uint64_t k, uint64_t nq, uint64_t nprobe, const float* vectors,
             const meta::DatesT& dates, QueryResults& results) = 0;
 
     virtual Status Size(uint64_t& result) = 0;
diff --git a/cpp/src/db/DBImpl.cpp b/cpp/src/db/DBImpl.cpp
index 1b6630ef84..ddee622669 100644
--- a/cpp/src/db/DBImpl.cpp
+++ b/cpp/src/db/DBImpl.cpp
@@ -189,11 +189,11 @@ Status DBImpl::InsertVectors(const std::string& table_id_,
 
 }
 
-Status DBImpl::Query(const std::string &table_id, uint64_t k, uint64_t nq,
+Status DBImpl::Query(const std::string &table_id, uint64_t k, uint64_t nq, uint64_t nprobe,
                       const float *vectors, QueryResults &results) {
     auto start_time = METRICS_NOW_TIME;
     meta::DatesT dates = {meta::Meta::GetDate()};
-    Status result = Query(table_id, k, nq, vectors, dates, results);
+    Status result = Query(table_id, k, nq, nprobe, vectors, dates, results);
     auto end_time = METRICS_NOW_TIME;
     auto total_time = METRICS_MICROSECONDS(start_time,end_time);
 
@@ -202,7 +202,7 @@ Status DBImpl::Query(const std::string &table_id, uint64_t k, uint64_t nq,
     return result;
 }
 
-Status DBImpl::Query(const std::string& table_id, uint64_t k, uint64_t nq,
+Status DBImpl::Query(const std::string& table_id, uint64_t k, uint64_t nq, uint64_t nprobe,
         const float* vectors, const meta::DatesT& dates, QueryResults& results) {
     ENGINE_LOG_DEBUG << "Query by vectors";
 
@@ -219,13 +219,13 @@ Status DBImpl::Query(const std::string& table_id, uint64_t k, uint64_t nq,
     }
 
     cache::CpuCacheMgr::GetInstance()->PrintInfo(); //print cache info before query
-    status = QueryAsync(table_id, file_id_array, k, nq, vectors, dates, results);
+    status = QueryAsync(table_id, file_id_array, k, nq, nprobe, vectors, dates, results);
     cache::CpuCacheMgr::GetInstance()->PrintInfo(); //print cache info after query
     return status;
 }
 
 Status DBImpl::Query(const std::string& table_id, const std::vector<std::string>& file_ids,
-        uint64_t k, uint64_t nq, const float* vectors,
+        uint64_t k, uint64_t nq, uint64_t nprobe, const float* vectors,
         const meta::DatesT& dates, QueryResults& results) {
     ENGINE_LOG_DEBUG << "Query by file ids";
 
@@ -256,20 +256,20 @@ Status DBImpl::Query(const std::string& table_id, const std::vector<std::string>
     }
 
     cache::CpuCacheMgr::GetInstance()->PrintInfo(); //print cache info before query
-    status = QueryAsync(table_id, file_id_array, k, nq, vectors, dates, results);
+    status = QueryAsync(table_id, file_id_array, k, nq, nprobe, vectors, dates, results);
     cache::CpuCacheMgr::GetInstance()->PrintInfo(); //print cache info after query
     return status;
 }
 
 Status DBImpl::QueryAsync(const std::string& table_id, const meta::TableFilesSchema& files,
-                          uint64_t k, uint64_t nq, const float* vectors,
+                          uint64_t k, uint64_t nq, uint64_t nprobe, const float* vectors,
                           const meta::DatesT& dates, QueryResults& results) {
     auto start_time = METRICS_NOW_TIME;
     server::TimeRecorder rc("");
 
     //step 1: get files to search
     ENGINE_LOG_DEBUG << "Engine query begin, index file count:" << files.size() << " date range count:" << dates.size();
-    SearchContextPtr context = std::make_shared<SearchContext>(k, nq, vectors);
+    SearchContextPtr context = std::make_shared<SearchContext>(k, nq, nprobe, vectors);
     for (auto &file : files) {
         TableFileSchemaPtr file_ptr = std::make_shared<meta::TableFileSchema>(file);
         context->AddIndexFile(file_ptr);
diff --git a/cpp/src/db/DBImpl.h b/cpp/src/db/DBImpl.h
index 969b7b0509..4aa7ac07bf 100644
--- a/cpp/src/db/DBImpl.h
+++ b/cpp/src/db/DBImpl.h
@@ -61,12 +61,18 @@ class DBImpl : public DB {
     InsertVectors(const std::string &table_id, uint64_t n, const float *vectors, IDNumbers &vector_ids) override;
 
     Status
-    Query(const std::string &table_id, uint64_t k, uint64_t nq, const float *vectors, QueryResults &results) override;
+    Query(const std::string &table_id,
+            uint64_t k,
+            uint64_t nq,
+            uint64_t nprobe,
+            const float *vectors,
+            QueryResults &results) override;
 
     Status
     Query(const std::string &table_id,
           uint64_t k,
           uint64_t nq,
+          uint64_t nprobe,
           const float *vectors,
           const meta::DatesT &dates,
           QueryResults &results) override;
@@ -76,6 +82,7 @@ class DBImpl : public DB {
           const std::vector<std::string> &file_ids,
           uint64_t k,
           uint64_t nq,
+          uint64_t nprobe,
           const float *vectors,
           const meta::DatesT &dates,
           QueryResults &results) override;
@@ -94,6 +101,7 @@ class DBImpl : public DB {
                const meta::TableFilesSchema &files,
                uint64_t k,
                uint64_t nq,
+               uint64_t nprobe,
                const float *vectors,
                const meta::DatesT &dates,
                QueryResults &results);
diff --git a/cpp/src/db/engine/ExecutionEngine.h b/cpp/src/db/engine/ExecutionEngine.h
index a122231a1d..88be75aeb9 100644
--- a/cpp/src/db/engine/ExecutionEngine.h
+++ b/cpp/src/db/engine/ExecutionEngine.h
@@ -51,6 +51,7 @@ public:
     virtual Status Search(long n,
                   const float *data,
                   long k,
+                  long nprobe,
                   float *distances,
                   long *labels) const = 0;
 
diff --git a/cpp/src/db/engine/ExecutionEngineImpl.cpp b/cpp/src/db/engine/ExecutionEngineImpl.cpp
index 037c52cf5c..dd38369832 100644
--- a/cpp/src/db/engine/ExecutionEngineImpl.cpp
+++ b/cpp/src/db/engine/ExecutionEngineImpl.cpp
@@ -228,10 +228,11 @@ ExecutionEngineImpl::BuildIndex(const std::string &location) {
 Status ExecutionEngineImpl::Search(long n,
                                    const float *data,
                                    long k,
+                                   long nprobe,
                                    float *distances,
                                    long *labels) const {
-    ENGINE_LOG_DEBUG << "Search Params: [k]  " << k << " [nprobe] " << nprobe_;
-    auto ec = index_->Search(n, data, distances, labels, Config::object{{"k", k}, {"nprobe", nprobe_}});
+    ENGINE_LOG_DEBUG << "Search Params: [k]  " << k << " [nprobe] " << nprobe;
+    auto ec = index_->Search(n, data, distances, labels, Config::object{{"k", k}, {"nprobe", nprobe}});
     if (ec != server::KNOWHERE_SUCCESS) {
         ENGINE_LOG_ERROR << "Search error";
         return Status::Error("Search: Search Error");
@@ -256,7 +257,6 @@ Status ExecutionEngineImpl::Init() {
         case EngineType::FAISS_IVFSQ8:
         case EngineType::FAISS_IVFFLAT: {
             ConfigNode engine_config = config.GetConfig(CONFIG_ENGINE);
-            nprobe_ = engine_config.GetInt32Value(CONFIG_NPROBE, 1);
             nlist_ = engine_config.GetInt32Value(CONFIG_NLIST, 16384);
             break;
         }
diff --git a/cpp/src/db/engine/ExecutionEngineImpl.h b/cpp/src/db/engine/ExecutionEngineImpl.h
index cb50af238b..948719310c 100644
--- a/cpp/src/db/engine/ExecutionEngineImpl.h
+++ b/cpp/src/db/engine/ExecutionEngineImpl.h
@@ -51,6 +51,7 @@ public:
     Status Search(long n,
                   const float *data,
                   long k,
+                  long nprobe,
                   float *distances,
                   long *labels) const override;
 
@@ -73,7 +74,6 @@ protected:
     int64_t dim;
     std::string location_;
 
-    size_t nprobe_ = 0;
     size_t nlist_ = 0;
     int64_t gpu_num = 0;
 };
diff --git a/cpp/src/db/scheduler/context/SearchContext.cpp b/cpp/src/db/scheduler/context/SearchContext.cpp
index 599686b5f4..87009f0a6b 100644
--- a/cpp/src/db/scheduler/context/SearchContext.cpp
+++ b/cpp/src/db/scheduler/context/SearchContext.cpp
@@ -13,10 +13,11 @@ namespace zilliz {
 namespace milvus {
 namespace engine {
 
-SearchContext::SearchContext(uint64_t topk, uint64_t nq, const float* vectors)
+SearchContext::SearchContext(uint64_t topk, uint64_t nq, uint64_t nprobe, const float* vectors)
     : IScheduleContext(ScheduleContextType::kSearch),
       topk_(topk),
       nq_(nq),
+      nprobe_(nprobe),
       vectors_(vectors) {
     //use current time to identify this context
     std::chrono::system_clock::time_point tp = std::chrono::system_clock::now();
diff --git a/cpp/src/db/scheduler/context/SearchContext.h b/cpp/src/db/scheduler/context/SearchContext.h
index 466fc435b4..9ca03e0830 100644
--- a/cpp/src/db/scheduler/context/SearchContext.h
+++ b/cpp/src/db/scheduler/context/SearchContext.h
@@ -21,12 +21,13 @@ using TableFileSchemaPtr = std::shared_ptr<meta::TableFileSchema>;
 
 class SearchContext : public IScheduleContext {
 public:
-    SearchContext(uint64_t topk, uint64_t nq, const float* vectors);
+    SearchContext(uint64_t topk, uint64_t nq, uint64_t nprobe, const float* vectors);
 
     bool AddIndexFile(TableFileSchemaPtr& index_file);
 
     uint64_t topk() const { return topk_; }
     uint64_t nq() const  { return nq_; }
+    uint64_t nprobe() const { return nprobe_; }
     const float* vectors() const { return vectors_; }
 
     using Id2IndexMap = std::unordered_map<size_t, TableFileSchemaPtr>;
@@ -53,6 +54,7 @@ public:
 private:
     uint64_t topk_ = 0;
     uint64_t nq_ = 0;
+    uint64_t nprobe_ = 10;
     const float* vectors_ = nullptr;
 
     Id2IndexMap map_index_files_;
diff --git a/cpp/src/db/scheduler/task/SearchTask.cpp b/cpp/src/db/scheduler/task/SearchTask.cpp
index 79baeeafe9..fd9d679d5e 100644
--- a/cpp/src/db/scheduler/task/SearchTask.cpp
+++ b/cpp/src/db/scheduler/task/SearchTask.cpp
@@ -109,12 +109,13 @@ std::shared_ptr<IScheduleTask> SearchTask::Execute() {
     for(auto& context : search_contexts_) {
         //step 1: allocate memory
         auto inner_k = context->topk();
+        auto nprobe = context->nprobe();
         output_ids.resize(inner_k*context->nq());
         output_distence.resize(inner_k*context->nq());
 
         try {
             //step 2: search
-            index_engine_->Search(context->nq(), context->vectors(), inner_k, output_distence.data(),
+            index_engine_->Search(context->nq(), context->vectors(), inner_k, nprobe, output_distence.data(),
                                   output_ids.data());
 
             double span = rc.RecordSection("do search for context:" + context->Identity());
diff --git a/cpp/src/sdk/examples/grpcsimple/src/ClientTest.cpp b/cpp/src/sdk/examples/grpcsimple/src/ClientTest.cpp
index ba009c0d94..583a917897 100644
--- a/cpp/src/sdk/examples/grpcsimple/src/ClientTest.cpp
+++ b/cpp/src/sdk/examples/grpcsimple/src/ClientTest.cpp
@@ -5,6 +5,7 @@
  ******************************************************************************/
 #include "ClientTest.h"
 #include "MilvusApi.h"
+#include "cache/CpuCacheMgr.h"
 
 #include <iostream>
 #include <time.h>
@@ -23,7 +24,7 @@ namespace {
     constexpr int64_t NQ = 10;
     constexpr int64_t TOP_K = 10;
     constexpr int64_t SEARCH_TARGET = 5000; //change this value, result is different
-    constexpr int64_t ADD_VECTOR_LOOP = 5;
+    constexpr int64_t ADD_VECTOR_LOOP = 1;
     constexpr int64_t SECONDS_EACH_HOUR = 3600;
 
 #define BLOCK_SPLITER std::cout << "===========================================" << std::endl;
@@ -174,7 +175,7 @@ namespace {
         std::vector<TopKQueryResult> topk_query_result_array;
         {
             TimeRecorder rc(phase_name);
-            Status stat = conn->Search(TABLE_NAME, record_array, query_range_array, TOP_K, topk_query_result_array);
+            Status stat = conn->Search(TABLE_NAME, record_array, query_range_array, TOP_K, 10, topk_query_result_array);
             std::cout << "SearchVector function call status: " << stat.ToString() << std::endl;
         }
 
@@ -316,6 +317,11 @@ ClientTest::Test(const std::string& address, const std::string& port) {
 //        std::cout << "BuildIndex function call status: " << stat.ToString() << std::endl;
     }
 
+    {//preload table
+        Status stat = conn->PreloadTable(TABLE_NAME);
+        std::cout << "PreloadTable function call status: " << stat.ToString() << std::endl;
+    }
+
     {//search vectors after build index finish
         DoSearch(conn, search_record_array, "Search after build index finish");
     }
diff --git a/cpp/src/sdk/grpc/ClientProxy.cpp b/cpp/src/sdk/grpc/ClientProxy.cpp
index f107a2694a..898f1c9528 100644
--- a/cpp/src/sdk/grpc/ClientProxy.cpp
+++ b/cpp/src/sdk/grpc/ClientProxy.cpp
@@ -210,12 +210,14 @@ ClientProxy::Search(const std::string &table_name,
                           const std::vector<RowRecord> &query_record_array,
                           const std::vector<Range> &query_range_array,
                           int64_t topk,
+                          int64_t nprobe,
                           std::vector<TopKQueryResult> &topk_query_result_array) {
     try {
         //step 1: convert vectors data
         ::milvus::grpc::SearchParam search_param;
         search_param.set_table_name(table_name);
         search_param.set_topk(topk);
+        search_param.set_nprobe(nprobe);
         for (auto &record : query_record_array) {
             ::milvus::grpc::RowRecord *row_record = search_param.add_query_record_array();
             for (auto &rec : record.data) {
diff --git a/cpp/src/sdk/grpc/ClientProxy.h b/cpp/src/sdk/grpc/ClientProxy.h
index c6da983bcc..f6a39f0445 100644
--- a/cpp/src/sdk/grpc/ClientProxy.h
+++ b/cpp/src/sdk/grpc/ClientProxy.h
@@ -47,6 +47,7 @@ public:
                     const std::vector<RowRecord> &query_record_array,
                     const std::vector<Range> &query_range_array,
                     int64_t topk,
+                    int64_t nprobe,
                     std::vector<TopKQueryResult> &topk_query_result_array) override;
 
     virtual Status
diff --git a/cpp/src/sdk/include/MilvusApi.h b/cpp/src/sdk/include/MilvusApi.h
index 22c6d23c8a..cb261743e1 100644
--- a/cpp/src/sdk/include/MilvusApi.h
+++ b/cpp/src/sdk/include/MilvusApi.h
@@ -247,6 +247,7 @@ class Connection {
                  const std::vector<RowRecord> &query_record_array,
                  const std::vector<Range> &query_range_array,
                  int64_t topk,
+                 int64_t nprobe,
                  std::vector<TopKQueryResult> &topk_query_result_array) = 0;
 
     /**
diff --git a/cpp/src/sdk/interface/ConnectionImpl.cpp b/cpp/src/sdk/interface/ConnectionImpl.cpp
index a0e4943197..b496d1c104 100644
--- a/cpp/src/sdk/interface/ConnectionImpl.cpp
+++ b/cpp/src/sdk/interface/ConnectionImpl.cpp
@@ -83,9 +83,10 @@ ConnectionImpl::Search(const std::string &table_name,
                              const std::vector<RowRecord> &query_record_array,
                              const std::vector<Range> &query_range_array,
                              int64_t topk,
+                             int64_t nprobe,
                              std::vector<TopKQueryResult> &topk_query_result_array) {
     return client_proxy_->Search(table_name, query_record_array, query_range_array, topk,
-                                       topk_query_result_array);
+                                 nprobe, topk_query_result_array);
 }
 
 Status
@@ -121,7 +122,7 @@ ConnectionImpl::DeleteByRange(Range &range,
 
 Status
 ConnectionImpl::PreloadTable(const std::string &table_name) const {
-
+    return client_proxy_->PreloadTable(table_name);
 }
 
 IndexParam
diff --git a/cpp/src/sdk/interface/ConnectionImpl.h b/cpp/src/sdk/interface/ConnectionImpl.h
index fa2c3d8497..24be6060ba 100644
--- a/cpp/src/sdk/interface/ConnectionImpl.h
+++ b/cpp/src/sdk/interface/ConnectionImpl.h
@@ -53,6 +53,7 @@ public:
                                 const std::vector<RowRecord> &query_record_array,
                                 const std::vector<Range> &query_range_array,
                                 int64_t topk,
+                                int64_t nprobe,
                                 std::vector<TopKQueryResult> &topk_query_result_array) override;
 
     virtual Status
diff --git a/cpp/src/server/grpc_impl/GrpcRequestTask.cpp b/cpp/src/server/grpc_impl/GrpcRequestTask.cpp
index 545c3cde9b..6d2842a34b 100644
--- a/cpp/src/server/grpc_impl/GrpcRequestTask.cpp
+++ b/cpp/src/server/grpc_impl/GrpcRequestTask.cpp
@@ -510,12 +510,17 @@ SearchTask::OnExecute() {
             return SetError(res, "Invalid table name: " + table_name_);
         }
 
-        int top_k_ = search_param_.topk();
+        int64_t top_k_ = search_param_.topk();
 
         if (top_k_ <= 0 || top_k_ > 1024) {
-            return SetError(SERVER_INVALID_TOPK, "Invalid topk: " + std::to_string(
-                    top_k_));
+            return SetError(SERVER_INVALID_TOPK, "Invalid topk: " + std::to_string(top_k_));
         }
+
+        int64_t nprobe = search_param_.nprobe();
+        if (nprobe <= 0) {
+            return SetError(SERVER_INVALID_NPROBE, "Invalid nprobe: " + std::to_string(nprobe));
+        }
+
         if (search_param_.query_record_array().empty()) {
             return SetError(SERVER_INVALID_ROWRECORD_ARRAY, "Row record array is empty");
         }
@@ -584,11 +589,11 @@ SearchTask::OnExecute() {
         auto record_count = (uint64_t) search_param_.query_record_array().size();
 
         if (file_id_array_.empty()) {
-            stat = DBWrapper::DB()->Query(table_name_, (size_t) top_k_, record_count, vec_f.data(),
+            stat = DBWrapper::DB()->Query(table_name_, (size_t) top_k_, record_count, nprobe, vec_f.data(),
                                           dates, results);
         } else {
-            stat = DBWrapper::DB()->Query(table_name_, file_id_array_,
-                                          (size_t) top_k_, record_count, vec_f.data(), dates, results);
+            stat = DBWrapper::DB()->Query(table_name_, file_id_array_, (size_t) top_k_,
+                                          record_count, nprobe, vec_f.data(), dates, results);
         }
 
         rc.ElapseFromBegin("search vectors from engine");
diff --git a/cpp/src/utils/Error.h b/cpp/src/utils/Error.h
index 0866d82955..c264e60b08 100644
--- a/cpp/src/utils/Error.h
+++ b/cpp/src/utils/Error.h
@@ -50,6 +50,8 @@ constexpr ServerError SERVER_ILLEGAL_VECTOR_ID = ToGlobalServerErrorCode(109);
 constexpr ServerError SERVER_ILLEGAL_SEARCH_RESULT = ToGlobalServerErrorCode(110);
 constexpr ServerError SERVER_CACHE_ERROR = ToGlobalServerErrorCode(111);
 constexpr ServerError SERVER_WRITE_ERROR = ToGlobalServerErrorCode(112);
+constexpr ServerError SERVER_INVALID_NPROBE = ToGlobalServerErrorCode(113);
+
 
 constexpr ServerError SERVER_LICENSE_FILE_NOT_EXIST = ToGlobalServerErrorCode(500);
 constexpr ServerError SERVER_LICENSE_VALIDATION_FAIL = ToGlobalServerErrorCode(501);
diff --git a/cpp/unittest/db/db_tests.cpp b/cpp/unittest/db/db_tests.cpp
index 229484b1cd..8b36d2efbd 100644
--- a/cpp/unittest/db/db_tests.cpp
+++ b/cpp/unittest/db/db_tests.cpp
@@ -8,6 +8,7 @@
 #include "db/DBImpl.h"
 #include "db/meta/MetaConsts.h"
 #include "db/Factories.h"
+#include "cache/CpuCacheMgr.h"
 
 #include <gtest/gtest.h>
 #include <easylogging++.h>
@@ -128,7 +129,7 @@ TEST_F(DBTest, DB_TEST) {
             prev_count = count;
 
             START_TIMER;
-            stat = db_->Query(TABLE_NAME, k, qb, qxb.data(), results);
+            stat = db_->Query(TABLE_NAME, k, qb, 10, qxb.data(), results);
             ss << "Search " << j << " With Size " << count/engine::meta::M << " M";
             STOP_TIMER(ss.str());
 
@@ -211,7 +212,7 @@ TEST_F(DBTest, SEARCH_TEST) {
 
     {
         engine::QueryResults results;
-        stat = db_->Query(TABLE_NAME, k, nq, xq.data(), results);
+        stat = db_->Query(TABLE_NAME, k, nq, 10, xq.data(), results);
         ASSERT_STATS(stat);
     }
 
@@ -219,13 +220,46 @@ TEST_F(DBTest, SEARCH_TEST) {
         engine::meta::DatesT dates;
         std::vector<std::string> file_ids = {"4", "5", "6"};
         engine::QueryResults results;
-        stat = db_->Query(TABLE_NAME, file_ids, k, nq, xq.data(), dates, results);
+        stat = db_->Query(TABLE_NAME, file_ids, k, nq, 10, xq.data(), dates, results);
         ASSERT_STATS(stat);
     }
 
     // TODO(linxj): add groundTruth assert
 };
 
+TEST_F(DBTest, PRELOADTABLE_TEST) {
+    engine::meta::TableSchema table_info = BuildTableSchema();
+    engine::Status stat = db_->CreateTable(table_info);
+
+    engine::meta::TableSchema table_info_get;
+    table_info_get.table_id_ = TABLE_NAME;
+    stat = db_->DescribeTable(table_info_get);
+    ASSERT_STATS(stat);
+    ASSERT_EQ(table_info_get.dimension_, TABLE_DIM);
+
+    engine::IDNumbers vector_ids;
+    engine::IDNumbers target_ids;
+
+    int64_t nb = 100000;
+    std::vector<float> xb;
+    BuildVectors(nb, xb);
+
+    int loop = 5;
+
+    for (auto i=0; i<loop; ++i) {
+        db_->InsertVectors(TABLE_NAME, nb, xb.data(), target_ids);
+        ASSERT_EQ(target_ids.size(), nb);
+    }
+    db_->BuildIndex(TABLE_NAME);
+
+    int64_t prev_cache_usage = cache::CpuCacheMgr::GetInstance()->CacheUsage();
+    stat = db_->PreloadTable(TABLE_NAME);
+    ASSERT_STATS(stat);
+    int64_t cur_cache_usage = cache::CpuCacheMgr::GetInstance()->CacheUsage();
+    ASSERT_TRUE(prev_cache_usage < cur_cache_usage);
+
+}
+
 TEST_F(DBTest2, ARHIVE_DISK_CHECK) {
 
     engine::meta::TableSchema table_info = BuildTableSchema();
@@ -309,4 +343,4 @@ TEST_F(DBTest2, DELETE_TEST) {
 
     db_->HasTable(TABLE_NAME, has_table);
     ASSERT_FALSE(has_table);
-};
+};
\ No newline at end of file
diff --git a/cpp/unittest/db/mem_test.cpp b/cpp/unittest/db/mem_test.cpp
index dc0b9aa77b..1976822e76 100644
--- a/cpp/unittest/db/mem_test.cpp
+++ b/cpp/unittest/db/mem_test.cpp
@@ -243,7 +243,7 @@ TEST_F(NewMemManagerTest, SERIAL_INSERT_SEARCH_TEST) {
     for (auto &pair : search_vectors) {
         auto &search = pair.second;
         engine::QueryResults results;
-        stat = db_->Query(TABLE_NAME, k, 1, search.data(), results);
+        stat = db_->Query(TABLE_NAME, k, 1, 10, search.data(), results);
         ASSERT_EQ(results[0][0].first, pair.first);
         ASSERT_LT(results[0][0].second, 0.00001);
     }
@@ -332,7 +332,7 @@ TEST_F(NewMemManagerTest, CONCURRENT_INSERT_SEARCH_TEST) {
             prev_count = count;
 
             START_TIMER;
-            stat = db_->Query(TABLE_NAME, k, qb, qxb.data(), results);
+            stat = db_->Query(TABLE_NAME, k, qb, 10, qxb.data(), results);
             ss << "Search " << j << " With Size " << count / engine::meta::M << " M";
             STOP_TIMER(ss.str());
 
diff --git a/cpp/unittest/db/mysql_db_test.cpp b/cpp/unittest/db/mysql_db_test.cpp
index 462721f186..78adf9f0f5 100644
--- a/cpp/unittest/db/mysql_db_test.cpp
+++ b/cpp/unittest/db/mysql_db_test.cpp
@@ -90,7 +90,7 @@ TEST_F(DISABLED_MySQLDBTest, DB_TEST) {
             prev_count = count;
 
             START_TIMER;
-            stat = db_->Query(TABLE_NAME, k, qb, qxb.data(), results);
+            stat = db_->Query(TABLE_NAME, k, qb, 10, qxb.data(), results);
             ss << "Search " << j << " With Size " << count/engine::meta::M << " M";
             STOP_TIMER(ss.str());
 
@@ -190,7 +190,7 @@ TEST_F(DISABLED_MySQLDBTest, SEARCH_TEST) {
     sleep(2); // wait until build index finish
 
     engine::QueryResults results;
-    stat = db_->Query(TABLE_NAME, k, nq, xq.data(), results);
+    stat = db_->Query(TABLE_NAME, k, nq, 10, xq.data(), results);
     ASSERT_STATS(stat);
 
     delete db_;
diff --git a/cpp/unittest/db/scheduler_test.cpp b/cpp/unittest/db/scheduler_test.cpp
index 01a7057e00..0937ef197a 100644
--- a/cpp/unittest/db/scheduler_test.cpp
+++ b/cpp/unittest/db/scheduler_test.cpp
@@ -38,7 +38,7 @@ TEST(DBSchedulerTest, TASK_QUEUE_TEST) {
     ASSERT_EQ(ptr, nullptr);
     ASSERT_TRUE(queue.Empty());
 
-    engine::SearchContextPtr context_ptr = std::make_shared<engine::SearchContext>(1, 1, nullptr);
+    engine::SearchContextPtr context_ptr = std::make_shared<engine::SearchContext>(1, 1, 10, nullptr);
     for(size_t i = 0; i < 10; i++) {
         auto file = CreateTabileFileStruct(i, "tbl");
         context_ptr->AddIndexFile(file);
@@ -69,7 +69,7 @@ TEST(DBSchedulerTest, SEARCH_SCHEDULER_TEST) {
         task_list.push_back(task_ptr);
     }
 
-    engine::SearchContextPtr context_ptr = std::make_shared<engine::SearchContext>(1, 1, nullptr);
+    engine::SearchContextPtr context_ptr = std::make_shared<engine::SearchContext>(1, 1, 10, nullptr);
     for(size_t i = 0; i < 20; i++) {
         auto file = CreateTabileFileStruct(i, "tbl");
         context_ptr->AddIndexFile(file);