diff --git a/cpp/src/db/DBImpl.cpp b/cpp/src/db/DBImpl.cpp
index 09a7c72201..c6365bc38b 100644
--- a/cpp/src/db/DBImpl.cpp
+++ b/cpp/src/db/DBImpl.cpp
@@ -229,7 +229,6 @@ void DBImpl::BackgroundTimerTask() {
     Status status;
     server::SystemInfo::GetInstance().Init();
     while (true) {
-        if (!bg_error_.ok()) break;
         if (shutting_down_.load(std::memory_order_acquire)){
             for(auto& iter : compact_thread_results_) {
                 iter.wait();
@@ -392,7 +391,7 @@ void DBImpl::BackgroundCompaction(std::set<std::string> table_ids) {
     for (auto& table_id : table_ids) {
         status = BackgroundMergeFiles(table_id);
         if (!status.ok()) {
-            bg_error_ = status;
+            ENGINE_LOG_ERROR << "Merge files for table " << table_id << " failed: " << status.ToString();
             return;
         }
     }
@@ -498,7 +497,7 @@ void DBImpl::BackgroundBuildIndex() {
         /* ENGINE_LOG_DEBUG << "Buiding index for " << file.location; */
         status = BuildIndex(file);
         if (!status.ok()) {
-            bg_error_ = status;
+            ENGINE_LOG_ERROR << "Building index for " << file.id_ << " failed: " << status.ToString();
             return;
         }
 
diff --git a/cpp/src/db/DBImpl.h b/cpp/src/db/DBImpl.h
index 5601f1a33b..012a445ef1 100644
--- a/cpp/src/db/DBImpl.h
+++ b/cpp/src/db/DBImpl.h
@@ -114,10 +114,8 @@ class DBImpl : public DB {
     BuildIndex(const meta::TableFileSchema &);
 
  private:
-
     const Options options_;
 
-    Status bg_error_;
     std::atomic<bool> shutting_down_;
 
     std::thread bg_timer_thread_;
diff --git a/cpp/src/db/ExecutionEngineImpl.cpp b/cpp/src/db/ExecutionEngineImpl.cpp
index 64aabb3777..ead97dfe38 100644
--- a/cpp/src/db/ExecutionEngineImpl.cpp
+++ b/cpp/src/db/ExecutionEngineImpl.cpp
@@ -37,14 +37,17 @@ VecIndexPtr ExecutionEngineImpl::CreatetVecIndex(EngineType type) {
     std::shared_ptr<VecIndex> index;
     switch (type) {
         case EngineType::FAISS_IDMAP: {
+            ENGINE_LOG_DEBUG << "Build Index: IDMAP";
             index = GetVecIndexFactory(IndexType::FAISS_IDMAP);
             break;
         }
         case EngineType::FAISS_IVFFLAT_GPU: {
+            ENGINE_LOG_DEBUG << "Build Index: IVFMIX";
             index = GetVecIndexFactory(IndexType::FAISS_IVFFLAT_MIX);
             break;
         }
         case EngineType::FAISS_IVFFLAT_CPU: {
+            ENGINE_LOG_DEBUG << "Build Index: IVFCPU";
             index = GetVecIndexFactory(IndexType::FAISS_IVFFLAT_CPU);
             break;
         }
@@ -135,6 +138,7 @@ ExecutionEngineImpl::BuildIndex(const std::string &location) {
 
     auto from_index = std::dynamic_pointer_cast<BFIndex>(index_);
     auto to_index = CreatetVecIndex(build_type);
+    ENGINE_LOG_DEBUG << "Build Params: [gpu_id]  " << gpu_num;
     to_index->BuildAll(Count(),
                        from_index->GetRawVectors(),
                        from_index->GetRawIds(),
@@ -148,6 +152,7 @@ Status ExecutionEngineImpl::Search(long n,
                                    long k,
                                    float *distances,
                                    long *labels) const {
+    ENGINE_LOG_DEBUG << "Search Params: [k]  " << k << " [nprobe] " << nprobe_;
     index_->Search(n, data, distances, labels, Config::object{{"k", k}, {"nprobe", nprobe_}});
     return Status::OK();
 }
@@ -169,7 +174,7 @@ Status ExecutionEngineImpl::Init() {
         }
         case EngineType::FAISS_IVFFLAT_CPU: {
             ConfigNode engine_config = config.GetConfig(CONFIG_ENGINE);
-            nprobe_ = engine_config.GetInt32Value(CONFIG_NPROBE, 1000);
+            nprobe_ = engine_config.GetInt32Value(CONFIG_NPROBE, 1);
             break;
         }
     }