storage/tsdb/tsdb.go
func (a adapter) Appender() (storage.Appender, error) {
	return appender{a: a.db.Appender()}, nil
}
func (a adapter) Appender() (storage.Appender, error) {
	return appender{a: a.db.Appender()}, nil
}
// Appender returns a new appender against the storage.