文档解释
ORA-55567: The _highthreshold_undoretention value should be at least string based on the current undo retention settings.
Cause: The _highthreshold_undoretention value was not greater than or equal to the UNDO_RETENTION setting and the low threshold value used for tuning undo retention.
Action: Reissue the SQL statement with a higher value.
：
ORA-55567错误指名了在当前undo retention设置下，_highthreshold_undoretention值必须是一个字符串。
官方解释
常见案例
一般处理方法及步骤
1.使用ALTER SYSTEM语句来设置_highthreshold_undoretention值：
ALTER SYSTEM SET “_highthreshold_undoretention” = ’15 minutes’;
2.重新启动实例，以使更改生效：
SHUTDOWN IMMEDIATE;
STARTUP;
