Extensible Optimizer and ORA03113 (endoffile on communication channel)

在测试通过extensible optimizer方法来解决table function的cardinality不准确的问题的时候 (关于什么是extensible optimizer以及如何设置可以参见这里) 居然遇到了ORA-03113的错误！

事情是这样的....

首先创建了一个table function...

CREATE OR REPLACE FUNCTION get_tab (p_cardinality IN INTEGER DEFAULT 1)
  RETURN t_tf_tab PIPELINED AS
BEGIN
  FOR i IN 1 .. 100 LOOP
    PIPE ROW (t_tf_row(i, 'Description for ' || i));
  END LOOP;

  RETURN;
END;
/

注意这个函数有个参数叫p_cardinality，这个参数的目的就是用来告诉extensible optimizer这个table function会返回多少条记录。注意到这个参数有个默认值为1，其实要强烈推荐不要给这个参数设置默认值。因为这个默认值在很大程度上会导致ORA-03113的错误，这个下面会提到。

创建了table function,现在来创建一个object type来实现ODCI中相关的接口函数....

CREATE OR REPLACE TYPE t_ptf_stats AS OBJECT (
  dummy INTEGER,
  
  STATIC FUNCTION ODCIGetInterfaces (
    p_interfaces OUT SYS.ODCIObjectList
  ) RETURN NUMBER,

  STATIC FUNCTION ODCIStatsTableFunction (
    p_function    IN  SYS.ODCIFuncInfo,
    p_stats       OUT SYS.ODCITabFuncStats,
    p_args        IN  SYS.ODCIArgDescList,
    p_cardinality IN INTEGER
  ) RETURN NUMBER
);
/

CREATE OR REPLACE TYPE BODY t_ptf_stats AS
  STATIC FUNCTION ODCIGetInterfaces (
    p_interfaces OUT SYS.ODCIObjectList
  ) RETURN NUMBER IS
  BEGIN
    p_interfaces := SYS.ODCIObjectList(
                      SYS.ODCIObject ('SYS', 'ODCISTATS2')
                    );
    RETURN ODCIConst.success;
  END ODCIGetInterfaces;

  STATIC FUNCTION ODCIStatsTableFunction (
                    p_function    IN  SYS.ODCIFuncInfo,
                    p_stats       OUT SYS.ODCITabFuncStats,
                    p_args        IN  SYS.ODCIArgDescList,
                    p_cardinality IN INTEGER
                  ) RETURN NUMBER IS
  BEGIN
    p_stats := SYS.ODCITabFuncStats(p_cardinality);  
    RETURN ODCIConst.success;
  END ODCIStatsTableFunction;
END;
/

注意函数ODCIStatsTableFunction中有一个自定义的参数，名为p_cardinality，这个名字必须跟上面定义的table function的参数名保持一致。ODCIStatsTableFunction的其他参数都是oracle预定义的参数，不能更改。

完成了这两步，接下来要把这个object type和刚才定义的table function关联起来，这样就可以通过这个object type来告诉CBO这个table function的cardinality该设置成多少。

ASSOCIATE STATISTICS WITH FUNCTIONS get_tab USING t_ptf_stats;

这里顺便提一下，如果要将table function和object type的关联解除，可以通过命令DISASSOCIATE STATISTICS FROM， 如下所示...

disassociate statistics from functions get_tab;

接下来就可以测试了。因为既然函数get_tab有个默认的参数值为1，那么可不可以不要设置这个参数呢？ （虽然get_tab实际上是返回100条数据）

SQL> select * from table(get_tab);

Execution Plan
----------------------------------------------------------
ERROR:
ORA-03113: end-of-file on communication channel


SP2-0612: Error generating AUTOTRACE EXPLAIN report

结果诡异的事情发生了！居然出现了end-of-file的错误，当前session被无情地关闭了！

搞了半天，最后发现当我设置了参数p_cardinality的时候，这个错误就消失了...

SQL> select * from table(get_tab(100));

Execution Plan
----------------------------------------------------------
Plan hash value: 3023735445

---------------------------------------------------------------------------------------------
| Id  | Operation                         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |         |   100 |   200 |    24   (0)| 00:00:01 |
|   1 |  COLLECTION ITERATOR PICKLER FETCH| GET_TAB |       |       |            |          |
---------------------------------------------------------------------------------------------

SQL> select * from table(get_tab(100000));

Execution Plan
----------------------------------------------------------
Plan hash value: 3023735445

---------------------------------------------------------------------------------------------
| Id  | Operation                         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |         |   100K|   195K|    25   (4)| 00:00:01 |
|   1 |  COLLECTION ITERATOR PICKLER FETCH| GET_TAB |       |       |            |          |
---------------------------------------------------------------------------------------------

SQL> select * from table(get_tab(10));

Execution Plan
----------------------------------------------------------
Plan hash value: 3023735445

---------------------------------------------------------------------------------------------
| Id  | Operation                         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |         |    10 |    20 |    24   (0)| 00:00:01 |
|   1 |  COLLECTION ITERATOR PICKLER FETCH| GET_TAB |       |       |            |          |
---------------------------------------------------------------------------------------------

SQL> select * from table(get_tab(1));

Execution Plan
----------------------------------------------------------
Plan hash value: 3023735445

---------------------------------------------------------------------------------------------
| Id  | Operation                         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |         |     1 |     2 |    24   (0)| 00:00:01 |
|   1 |  COLLECTION ITERATOR PICKLER FETCH| GET_TAB |       |       |            |          |
---------------------------------------------------------------------------------------------

所以在调用get_tab的时候必须给参数赋值，这个真的很奇怪！ 

另外还有个问题很奇怪，不能像如下这种方式调用get_tab, 

SQL> select * from table(get_table(p_cardinality=>100));

也就是不能指定参数名p_cardinality， 否则就会报出一个更加无厘头的错误....

SQL> select * from table(get_table(p_cardinality=>100));      
 select * from table(get_table(p_cardinality=>100))                                                       
                                            *                  
ERROR at line 1:                                              
ORA-00907: missing right parenthesis                                                                                        

哎，看来用extensible optimizer还是有风险的~~~