diff --git a/cpp/conf/log_config.conf b/cpp/conf/log_config.conf
index 80710b570e92c5b4cb8418204f448261ceb5082c..79a3965719934f329932320efbb81dd8673deeaf 100644
--- a/cpp/conf/log_config.conf
+++ b/cpp/conf/log_config.conf
@@ -20,8 +20,8 @@
     TO_STANDARD_OUTPUT      =   false
 ## Error logs
 * ERROR:
-    ENABLED                 =   false
+    ENABLED                 =   true
     FILENAME                =   "/tmp/milvus/logs/milvus-%datetime{%H:%m}-error.log"
 * FATAL:
-    ENABLED                 =   false
+    ENABLED                 =   true
     FILENAME                =   "/tmp/milvus/logs/milvus-%datetime{%H:%m}-fatal.log"
\ No newline at end of file
diff --git a/cpp/conf/server_config.yaml b/cpp/conf/server_config.yaml
index bcf9d2116dfd58a06fa24a340a71342e0197a1b2..33858c9455edde95eb961b82d469f5a87f458014 100644
--- a/cpp/conf/server_config.yaml
+++ b/cpp/conf/server_config.yaml
@@ -1,15 +1,15 @@
 server_config:
   address: 0.0.0.0
-  port: 19530                 # the port milvus listen to, default: 19530, range: 1025 ~ 65534
+  port: 19531               # the port milvus listen to, default: 19530, range: 1025 ~ 65534
   gpu_index: 0                # the gpu milvus use, default: 0, range: 0 ~ gpu number - 1
-  mode: single                # milvus deployment type: single, cluster
+  mode: cluster                # milvus deployment type: single, cluster
 
 db_config:
   db_path: /tmp/milvus             # milvus data storage path
   #URI format: dialect://username:password@host:port/database
   #All parts except dialect are optional, but you MUST include the delimiters
   #Currently supports mysql or sqlite
-  db_backend_url: dialect://username:password@host:port/database # meta database uri
+  db_backend_url: mysql://root:1234@:/test # meta database uri
   index_building_threshold: 1024   # index building trigger threshold, default: 1024, unit: MB
 
 metric_config:
diff --git a/cpp/src/db/MySQLConnectionPool.h b/cpp/src/db/MySQLConnectionPool.h
index ebb2c5eb54e6966f660138e798e3fb53dc1a0a25..8a240102dce5184c5ea53407e65c06624de7666e 100644
--- a/cpp/src/db/MySQLConnectionPool.h
+++ b/cpp/src/db/MySQLConnectionPool.h
@@ -54,10 +54,12 @@ public:
     void release(const mysqlpp::Connection* pc) override {
         mysqlpp::ConnectionPool::release(pc);
 //        ENGINE_LOG_DEBUG << "conns_in_use_ in release: " << conns_in_use_ << std::endl;
-        --conns_in_use_;
-        if (conns_in_use_ < 0) {
+        if (conns_in_use_ <= 0) {
             ENGINE_LOG_WARNING << "MySQLConnetionPool::release: conns_in_use_ is less than zero.  conns_in_use_ = " << conns_in_use_ << std::endl;
         }
+        else {
+            --conns_in_use_;
+        }
     }
 
     void set_max_idle_time(int max_idle) {