在测试SQL 运行时统计特性时发现使用dbms_xplan.display_cursor 是出下面的错误

SQL>SELECT * FROM table(dbms_xplan.display_cursor(NULL,NULL, 'iostats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  9babjv8yq8ru3, child number 0
BEGIN DBMS_OUTPUT.GET_LINES(:LINES, :NUMLINES); END;
NOTE: cannot fetch plan for SQL_ID: 9babjv8yq8ru3, CHILD_NUMBER: 0
      Please verify value of SQL_ID and CHILD_NUMBER;
      It could also be that the plan is no longer in cursor cache (check v$sql_plan)

8 rows selected.
 

造成错误原因是SQLPLUS的环境变量 serveroutput 设置为了ON

SQL>show serveroutput
serveroutput ON SIZE 10000 FORMAT WORD_WRAPPED
SQL>set serveroutput OFF --关闭serveroutput
 

关闭后你应该可以看到

SQL>select /*+  gather_plan_statistics*/ count(*) from scott.DEPT;   
  COUNT(*)
----------
         4
1 row selected.
Elapsed: 00:00:00.00
SQL>SELECT * FROM table(dbms_xplan.display_cursor(NULL,NULL, 'iostats last'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  0hgxnuw37sbrx, child number 0
-------------------------------------
select /*+  gather_plan_statistics*/ count(*) from scott.DEPT
Plan hash value: 3051237957
--------------------------------------------------------------------------------------
| Id  | Operation        | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |         |      1 |        |      1 |00:00:00.01 |       1 |
|   1 |  SORT AGGREGATE  |         |      1 |      1 |      1 |00:00:00.01 |       1 |
|   2 |   INDEX FULL SCAN| PK_DEPT |      1 |      4 |      4 |00:00:00.01 |       1 |
--------------------------------------------------------------------------------------

14 rows selected.
Elapsed: 00:00:00.02