diff --git a/common/dbconnector.cpp b/common/dbconnector.cpp
index d4969c458..d5b08eeba 100644
--- a/common/dbconnector.cpp
+++ b/common/dbconnector.cpp
@@ -6,6 +6,7 @@
 #include <system_error>
 #include <fstream>
 #include "json.hpp"
+#include "logger.h"
 
 #include "common/dbconnector.h"
 #include "common/redisreply.h"
@@ -17,8 +18,14 @@ namespace swss {
 
 void SonicDBConfig::initialize(const string &file)
 {
+
+    SWSS_LOG_ENTER();
+
     if (m_init)
+    {
+        SWSS_LOG_ERROR("SonicDBConfig already initialized");
         throw runtime_error("SonicDBConfig already initialized");
+    }
 
     ifstream i(file);
     if (i.good())
@@ -47,48 +54,55 @@ void SonicDBConfig::initialize(const string &file)
         }
         catch (domain_error& e)
         {
+            SWSS_LOG_ERROR("key doesn't exist in json object, NULL value has no iterator >> %s\n", e.what());
             throw runtime_error("key doesn't exist in json object, NULL value has no iterator >> " + string(e.what()));
         }
         catch (exception &e)
         {
+            SWSS_LOG_ERROR("Sonic database config file syntax error >> %s\n", e.what());
             throw runtime_error("Sonic database config file syntax error >> " + string(e.what()));
         }
     }
+    else
+    {
+        SWSS_LOG_ERROR("Sonic database config file doesn't exist at %s\n", file.c_str());
+        throw runtime_error("Sonic database config file doesn't exist at " + file);
+    }
 }
 
 string SonicDBConfig::getDbInst(const string &dbName)
 {
     if (!m_init)
         initialize();
-    return m_db_info[dbName].first;
+    return m_db_info.at(dbName).first;
 }
 
 int SonicDBConfig::getDbId(const string &dbName)
 {
     if (!m_init)
         initialize();
-    return m_db_info[dbName].second;
+    return m_db_info.at(dbName).second;
 }
 
 string SonicDBConfig::getDbSock(const string &dbName)
 {
     if (!m_init)
         initialize();
-    return m_inst_info[getDbInst(dbName)].first;
+    return m_inst_info.at(getDbInst(dbName)).first;
 }
 
 string SonicDBConfig::getDbHostname(const string &dbName)
 {
     if (!m_init)
         initialize();
-    return m_inst_info[getDbInst(dbName)].second.first;
+    return m_inst_info.at(getDbInst(dbName)).second.first;
 }
 
 int SonicDBConfig::getDbPort(const string &dbName)
 {
     if (!m_init)
         initialize();
-    return m_inst_info[getDbInst(dbName)].second.second;
+    return m_inst_info.at(getDbInst(dbName)).second.second;
 }
 
 constexpr const char *SonicDBConfig::DEFAULT_SONIC_DB_CONFIG_FILE;
diff --git a/tests/redis_multi_db_ut.cpp b/tests/redis_multi_db_ut.cpp
index 69029b276..9698526ee 100644
--- a/tests/redis_multi_db_ut.cpp
+++ b/tests/redis_multi_db_ut.cpp
@@ -13,13 +13,56 @@ using json = nlohmann::json;
 TEST(DBConnector, multi_db_test)
 {
     string file = "./tests/redis_multi_db_ut_config/database_config.json";
+    string nonexisting_file = "./tests/redis_multi_db_ut_config/database_config_nonexisting.json";
+
     // by default , init should be false
     cout<<"Default : isInit = "<<SonicDBConfig::isInit()<<endl;
-    EXPECT_EQ(SonicDBConfig::isInit(), false);
+    EXPECT_FALSE(SonicDBConfig::isInit());
+
+
+    // load nonexisting file, should throw exception with NO file existing
+    try
+    {
+        cout<<"INIT: loading nonexisting db config file"<<endl;
+        SonicDBConfig::initialize(nonexisting_file);
+    }
+    catch (exception &e)
+    {
+        EXPECT_TRUE(strstr(e.what(), "Sonic database config file doesn't exist"));
+    }
+    EXPECT_FALSE(SonicDBConfig::isInit());
+
     // load local config file, init should be true
     SonicDBConfig::initialize(file);
-    cout<<"INIT : load local db config file, isInit = "<<SonicDBConfig::isInit()<<endl;
-    EXPECT_EQ(SonicDBConfig::isInit(), true);
+    cout<<"INIT: load local db config file, isInit = "<<SonicDBConfig::isInit()<<endl;
+    EXPECT_TRUE(SonicDBConfig::isInit());
+
+    // load local config file again, should throw exception with init already done
+    try
+    {
+        cout<<"INIT: loading local config file again"<<endl;
+        SonicDBConfig::initialize(file);
+    }
+    catch (exception &e)
+    {
+        EXPECT_TRUE(strstr(e.what(), "SonicDBConfig already initialized"));
+    }
+
+    //Invalid DB name input
+    cout<<"GET: invalid dbname input for getDbInst()"<<endl;
+    EXPECT_THROW(SonicDBConfig::getDbInst("INVALID_DBNAME"), out_of_range);
+
+    cout<<"GET: invalid dbname input for getDbId()"<<endl;
+    EXPECT_THROW(SonicDBConfig::getDbId("INVALID_DBNAME"), out_of_range);
+
+    cout<<"GET: invalid dbname input for getDbSock()"<<endl;
+    EXPECT_THROW(SonicDBConfig::getDbSock("INVALID_DBNAME"), out_of_range);
+
+    cout<<"GET: invalid dbname input for getDbHostname()"<<endl;
+    EXPECT_THROW(SonicDBConfig::getDbHostname("INVALID_DBNAME"), out_of_range);
+
+    cout<<"GET: invalid dbname input for getDbPort()"<<endl;
+    EXPECT_THROW(SonicDBConfig::getDbPort("INVALID_DBNAME"), out_of_range);
 
     // parse config file
     ifstream i(file);