Reference cursor gets lost in XMLType.createxml

Question

I am calling a function that returns a reference cursor, and I am using XMLType.createxml to convert the results to XML, e.g.

select XMLType.createxml(package_name.storedProcName('PARAM1', 'PARAM2', 'PARAM3')) as sresult from dual;

However, I have found this to have an unwelcome side-effect. It seems that the cursor used to retrieve the data for the XMLType is never closed. After calling the function many times using this technique, I always run into the following error:

ORA-01000: maximum open cursors exceeded

I do not have a handle to the cursor, thus I cannot manually close it. Also, we are using pooled connections, so there is no connection reset where these cursors can be automatically released. What can be done about this?

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Here is my Oracle version (as returned from v$version):

Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi
PL/SQL Release 10.2.0.5.0 - Production                          
CORE    10.2.0.5.0  Production                                      
TNS for HPUX: Version 10.2.0.5.0 - Production                   
NLSRTL Version 10.2.0.5.0 - Production

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(For those interested, here is a link to my previous question related to XMLType.)

Answer 1

There seems to be a bug, you should open a service request to Oracle support. I'll post a test case that reproduces your finding in 9i and 11.2.0.3:

SQL> SHOW parameter open_cursors

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
open_cursors                         integer     600

SQL> CREATE OR REPLACE FUNCTION ret_cursor RETURN SYS_REFCURSOR IS
  2     l SYS_REFCURSOR;
  3  BEGIN
  4     OPEN l FOR
  5        SELECT * FROM dual;
  6     RETURN l;
  7  END;
  8  /

Function created

XMLType will not close cursors correctly when called with the above function, whereas it works well with static SQL:

SQL> /* Works as expected with static cursor */
  2  DECLARE
  3     l XMLTYPE;
  4  BEGIN
  5     FOR i IN 1 .. 1e4 LOOP
  6        SELECT xmltype.createXML(CURSOR(SELECT * FROM DUAL)) INTO l FROM dual;
  7     END LOOP;
  8  END;
  9  /      

PL/SQL procedure successfully completed

SQL> /* Fails with call to dynamic cursor */
SQL> DECLARE
  2     l XMLTYPE;
  3  BEGIN
  4     FOR i IN 1 .. 1e4 LOOP
  5        SELECT xmltype.createXML(ret_cursor) INTO l FROM dual;
  6     END LOOP;
  7  END;
  8  /
DECLARE
*
ERROR at line 1:
ORA-01000: maximum open cursors exceeded
ORA-06512: at "APPS.RET_CURSOR", line 4
ORA-06512: at line 5

You should be able to use a wrapper function to prevent the ORA-01000 from happening (tested on 9iR2, 11gR2):

SQL> CREATE OR REPLACE FUNCTION wrap_xml(p SYS_REFCURSOR) RETURN XMLTYPE IS
  2     l XMLTYPE;
  3  BEGIN
  4     l := xmltype.CreateXML(p);
  5     IF p%ISOPEN THEN
  6        CLOSE p;
  7     END IF;
  8     RETURN l;
  9  END;
 10  /

Function created

SQL> DECLARE
  2     l XMLTYPE;
  3  BEGIN
  4     FOR i IN 1 .. 1e4 LOOP
  5        l := wrap_xml(ret_cursor); -- a SELECT FROM dual will still fail here
  6                                   -- on 9i but not on 11g 
  7     END LOOP;
  8  END;
  9  /

PL/SQL procedure successfully completed