想要做执行计划的用户名是sess，错误是这样的：
SQL> conn sess/sess
Connected.
SQL> set autotrace on; 
SP2-0613: Unable to verify PLAN_TABLE format or existence
SP2-0611: Error enabling EXPLAIN report


解决方法：
1.登陆sysdba，执行脚本plustrce.sql
SQL> conn / as sysdba
Connected.
SQL> @?/sqlplus/admin/plustrce.sql

2.将角色plustrace赋给用户
SQL> grant plustrace to sess;

Grant succeeded.

3.登陆当前用户，执行脚本utlxplan.sql
SQL> conn sess/sess
Connected.
SQL> @?/rdbms/admin/utlxplan.sql

Table created.

之后，再想要做执行计划就没有错误提示了
SQL> set  autotrace traceonly;
SQL>

参考metalink  doc ID 116091.1 SET AUTOTRACE ON fails with SP2-0613 SP2-0611 SP2-0618 SP2- 0612