diff --git a/common/db.go b/common/db.go
index 27a07dc..a9c315d 100644
--- a/common/db.go
+++ b/common/db.go
@@ -44,12 +44,6 @@ func (m *DB) Must() *DB {
 	return &DB{DB: db}
 }
 
-// NoMust unset must flag, don't panic when error occur
-func (m *DB) NoMust() *DB {
-	db := m.InstanceSet("ivy.must", false)
-	return &DB{DB: db}
-}
-
 // ToSQLDB get the sql.DB
 func (m *DB) ToSQLDB() *sql.DB {
 	d, err := m.DB.DB()
diff --git a/common/types.go b/common/types.go
index f95daf7..7577db0 100644
--- a/common/types.go
+++ b/common/types.go
@@ -13,10 +13,6 @@ import (
 	"github.com/go-redis/redis/v8"
 )
 
-func GetDriver() string {
-	return Config.Store.Driver
-}
-
 var rdb *redis.Client
 var once sync.Once
 
diff --git a/common/types_test.go b/common/types_test.go
index 7890c6c..8aea076 100644
--- a/common/types_test.go
+++ b/common/types_test.go
@@ -24,8 +24,6 @@ func testSql(t *testing.T) {
 	db := DbGet(Config.Store.GetDBConf())
 	err := func() (rerr error) {
 		defer dtmimp.P2E(&rerr)
-		dbr := db.NoMust().Exec("select a")
-		assert.NotEqual(t, nil, dbr.Error)
 		db.Must().Exec("select a")
 		return nil
 	}()
diff --git a/conf.sample.yml b/conf.sample.yml
index 79a9fe2..c6b12ba 100644
--- a/conf.sample.yml
+++ b/conf.sample.yml
@@ -1,33 +1,41 @@
-# Store:
+# Store: # specify which engine to store trans status
+#   Driver: 'boltdb' # default store engine
+
 #   Driver: 'redis'
 #   Host: 'localhost'
 #   User: ''
 #   Password: ''
 #   Port: 6379
 
-# driver: 'postgres'
-# host: 'localhost'
-# user: 'postgres'
-# password: 'mysecretpassword'
-# port: '5432'
+#   Driver: 'mysql'
+#   Host: 'localhost'
+#   User: 'root'
+#   Password: ''
+#   Port: 3306
+
+#   Driver: 'postgres'
+#   Host: 'localhost'
+#   User: 'postgres'
+#   Password: 'mysecretpassword'
+#   Port: '5432'
+
+### following connection config is for only Driver postgres/mysql
+#   MaxOpenConns: 500
+#   MaxIdleConns: 500
+#   ConnMaxLifeTime 5 # default value is 5 (minutes)
 
-# MaxOpenConns: 499
-# max_idle_conns: 'dbmaxidleconns'
-# conn_max_life_time: 'dbconnmaxlifetime'
 # MicroService:
 #   Driver: 'dtm-driver-gozero' # name of the driver to handle register/discover
 #   Target: 'etcd://localhost:2379/dtmservice' # register dtm server to this url
 #   EndPoint: 'localhost:36790'
 
-# MicroService:
-#   Driver: 'dtm-driver-protocol1'
-
 # the unit of following configurations is second
 
 # TransCronInterval: 3 # the interval to poll unfinished global transaction for every dtm process
 # TimeoutToFail: 35 # timeout for XA, TCC to fail. saga's timeout default to infinite, which can be overwritten in saga options
 # RetryInterval: 10 # the subtrans branch will be retried after this interval
 
+### db config of examples
 ExamplesDB:
   Driver: 'mysql'
   Host: 'localhost'