diff --git a/cpp/src/db/DBImpl.cpp b/cpp/src/db/DBImpl.cpp
index e39942d35d776c2ed0b706af75245a9ab7d3d933..c7ee986c96373afb600faa456cf0b0f9acd1e573 100644
--- a/cpp/src/db/DBImpl.cpp
+++ b/cpp/src/db/DBImpl.cpp
@@ -600,6 +600,7 @@ void DBImpl::BackgroundCompaction(std::set<std::string> table_ids) {
     int ttl = 1;
     if (options_.mode == "cluster") {
         ttl = meta::D_SEC;
+        ENGINE_LOG_DEBUG << "Server mode is cluster. Clean up files with ttl = " << std::to_string(ttl) << "seconds.";
     }
     meta_ptr_->CleanUpFilesWithTTL(ttl);
 }
diff --git a/cpp/src/db/MySQLConnectionPool.h b/cpp/src/db/MySQLConnectionPool.h
index 98b7f6789527b3a9e8945e522bf45b233abf2de3..ebb2c5eb54e6966f660138e798e3fb53dc1a0a25 100644
--- a/cpp/src/db/MySQLConnectionPool.h
+++ b/cpp/src/db/MySQLConnectionPool.h
@@ -56,7 +56,7 @@ public:
 //        ENGINE_LOG_DEBUG << "conns_in_use_ in release: " << conns_in_use_ << std::endl;
         --conns_in_use_;
         if (conns_in_use_ < 0) {
-            ENGINE_LOG_ERROR << "MySQLConnetionPool::release: conns_in_use_ is less than zero.  conns_in_use_ = " << conns_in_use_ << std::endl;
+            ENGINE_LOG_WARNING << "MySQLConnetionPool::release: conns_in_use_ is less than zero.  conns_in_use_ = " << conns_in_use_ << std::endl;
         }
     }
 
diff --git a/cpp/src/db/MySQLMetaImpl.cpp b/cpp/src/db/MySQLMetaImpl.cpp
index 116636be764930181ae4efb7b2fafde0234935f2..40ff30b88af4a7c60ac9e8e385e01f7e3f6dead4 100644
--- a/cpp/src/db/MySQLMetaImpl.cpp
+++ b/cpp/src/db/MySQLMetaImpl.cpp
@@ -448,9 +448,10 @@ namespace meta {
                 Query deleteTableFilesQuery = connectionPtr->query();
                 //
                 deleteTableFilesQuery << "UPDATE TableFiles " <<
-                                      "SET state = " << std::to_string(TableSchema::TO_DELETE) << ", " <<
+                                      "SET file_type = " << std::to_string(TableSchema::TO_DELETE) << ", " <<
                                       "updated_time = " << std::to_string(utils::GetMicroSecTimeStamp()) << " " <<
-                                      "WHERE table_id = " << quote << table_id << ";";
+                                      "WHERE table_id = " << quote << table_id << " AND " <<
+                                      "file_type <> " << std::to_string(TableSchema::TO_DELETE) << ";";
 
                 if (!deleteTableFilesQuery.exec()) {
                     ENGINE_LOG_ERROR << "QUERY ERROR WHEN DELETING TABLE FILES";
diff --git a/cpp/src/server/DBWrapper.cpp b/cpp/src/server/DBWrapper.cpp
index c38c5d8843345ac54b8f84997fd33b8649106721..6ad308a8d6cbbedb5addab20d1ed87f27f55f810 100644
--- a/cpp/src/server/DBWrapper.cpp
+++ b/cpp/src/server/DBWrapper.cpp
@@ -23,7 +23,9 @@ DBWrapper::DBWrapper() {
     if(index_size > 0) {//ensure larger than zero, unit is MB
         opt.index_trigger_size = (size_t)index_size * engine::ONE_MB;
     }
-    opt.mode = config.GetValue(CONFIG_CLUSTER_MODE, "single");
+    ConfigNode& serverConfig = ServerConfig::GetInstance().GetConfig(CONFIG_SERVER);
+    opt.mode = serverConfig.GetValue(CONFIG_CLUSTER_MODE, "single");
+//    std::cout << "mode = " << opt.mode << std::endl;
 
     CommonUtil::CreateDirectory(opt.meta.path);