3.0.4から3.1へのアップグレード中，次のようなメッセージが出てきました．どのように対策をしたら良いかご教示ください．
mod_data
データベースの読み込み中にエラーが発生しました。
Debug info:Can't find file: './performance_schema/session_variables.frm' (errno: 13 - Permission denied)
SHOW VARIABLES LIKE 'innodb_file_per_table'
[array (
)]
Error code: dmlreadexception
Stack trace:
- line 474 of /lib/dml/moodle_database.php: dml_read_exception thrown
- line 1088 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
- line 1527 of /lib/dml/moodle_database.php: call to mysqli_native_moodle_database->get_records_sql()
- line 332 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->get_record_sql()
- line 308 of /lib/ddl/mysql_sql_generator.php: call to mysqli_native_moodle_database->is_compressed_row_format_supported()
- line 542 of /lib/ddl/database_manager.php: call to mysql_sql_generator->getAddFieldSQL()
- line 74 of /mod/data/db/upgrade.php: call to database_manager->add_field()
- line 726 of /lib/upgradelib.php: call to xmldb_data_upgrade()
- line 432 of /lib/upgradelib.php: call to upgrade_plugins_modules()
- line 1742 of /lib/upgradelib.php: call to upgrade_plugins()
- line 677 of /admin/index.php: call to upgrade_noncore()