mysqliに変えました。
エラーメッセージが変化したので、mysqliの効果はあったようですが、
うまくいっていません。

MySQLへの接続ができていないことは理解できるのですが、対応方法がわかりません。
よろしくお願いいたします。

次のメッセージは以下
019/10/13 09:38:39 [/******/admin/index.php] Fatal error(E_USER_ERROR): DB処理でエラーが発生しました。
SQL: [SET SESSION default_storage_engine = InnoDB]
MDB2 Error: connect failed
_doConnect: [Error message: unable to establish a connection]
[Native code: 0]
on [/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/SC_Query.php(1103)] from ::1
login_id = ()[vpv95gl73kurhvg19slr48jn86]
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/html/admin/index.php(23): require_once
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/html/admin/require.php(31): require_once
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/require_base.php(43): SC_SessionFactory_UseCookie->initSession
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/sessionfactory/SC_SessionFactory_UseCookie.php(53): session_start
(): SC_Helper_Session->sfSessRead
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊data/class/helper/SC_Helper_Session.php(71): SC_Query::getSingletonInstance
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/SC_Query.php(113): SC_Query->__construct
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/SC_Query.php(96): SC_DB_DBFactory_MYSQL->initObjQuery
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/db/dbfactory/SC_DB_DBFactory_MYSQL.php(376): SC_Query->exec
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/SC_Query.php(263): SC_Query->query
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊data/class/SC_Query.php(876): SC_Query->prepare
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/SC_Query.php(1032): SC_Query->error
/＊＊＊＊＊＊＊＊＊＊＊＊＊＊/data/class/SC_Query.php(1103): trigger_error
2019/10/13 09:38:45 [/******/html/index.php] Fatal error(E_USER_ERROR): DB処理でエラーが発生しました。