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Two questions about stored outlines

August 29, 2009

Out of a discussion with a colleague at work I had two questions to answer:

  1. Can a stored outline change a query – e.g. the FROM or WHERE clauses?

  2. If a stored outline hints the query to use a function-based index, and a user doesn’t have execute privilege on the function, what happens if the user runs the query?

1. Can a stored outline change a query?

The answer was simple to find – no, stored outlines only comprise hints; if the hint doesn’t make sense for a particular query, the optimiser ignores the hint just as it does if you add the hint directly to the query. For example:


SQL> CONN SYS AS SYSDBA

SQL> ALTER SYSTEM SET USE_STORED_OUTLINES = TRUE;

SQL> GRANT CREATE ANY OUTLINE TO SCOTT;

SQL> CONN SCOTT

SQL> CREATE OUTLINE testoutline1 ON
SELECT * FROM EMP WHERE EMPNO = :1;

SQL> CREATE OUTLINE testoutline2 ON
SELECT * FROM DEPT WHERE DEPTNO = :1;

SQL> CONN SYS AS SYSDBA

–swap the outlines
SQL> UPDATE OUTLN.ol$hints
SET ol_name =
CASE ol_name
WHEN ‘TESTOUTLINE1′ THEN ‘TESTOUTLINE2′
WHEN ‘TESTOUTLINE2′ THEN ‘TESTOUTLINE1′
END
WHERE ol_name IN (‘TESTOUTLINE1′,’TESTOUTLINE2′);

SQL> CONN SCOTT

SQL> SELECT * FROM EMP WHERE EMPNO = :1;

SELECT STATEMENT
TABLE ACCESS BY INDEX ROWID (EMP)
INDEX UNIQUE SCAN (PK_EMP)

2. What if a user doesn’t have execute privilege on a function used in a function-based index, but the stored outline tells them to use the index?

The scenario is where a table has an index on a column and a function. A stored outline could tell the optimiser to use this index, but a particular user doesn’t have execute privilege on the function; will the the optimiser still allow the user to query the table using the index? It should, since you shouldn’t need to execute the function to do a range scan on the first column, ignoring the function-based portion of the index.


SQL> CONN SCOTT

SQL> CREATE TABLE SCOTT.testtable
(c1 NUMBER NOT NULL
,c2 NUMBER NOT NULL
);

SQL> GRANT SELECT ON SCOTT.testtable TO LARRY;

SQL> CREATE OR REPLACE
FUNCTION SCOTT.testfunction (i NUMBER)
RETURN NUMBER DETERMINISTIC IS
BEGIN
RETURN I * 3.14159;
END;

–note: don’t grant execute on testfunction to LARRY

SQL> CREATE INDEX SCOTT.testindex
ON SCOTT.testtable (c1, SCOTT.testfunction(c2));

SQL> CONN LARRY

SQL> SELECT * FROM SCOTT.testtable
WHERE c1 = TO_NUMBER(:1);

SELECT STATEMENT
TABLE ACCESS FULL (TESTTABLE)

SQL> CREATE OUTLINE testoutline3 ON
SELECT * FROM SCOTT.testtable x
WHERE c1 = TO_NUMBER(:1)
AND SCOTT.testfunction(c2) = TO_NUMBER(:2);

SQL> CREATE OUTLINE testoutline4 ON
SELECT * FROM SCOTT.testtable x
WHERE c1 = TO_NUMBER(:1);

SQL> CONN SYS

–swap the outlines
SQL> UPDATE OUTLN.ol$hints
SET ol_name =
CASE ol_name
WHEN ‘TESTOUTLINE3′ THEN ‘TESTOUTLINE4′
WHEN ‘TESTOUTLINE4′ THEN ‘TESTOUTLINE3′
END
WHERE ol_name IN (‘TESTOUTLINE3′,’TESTOUTLINE4′);

SQL> CONN LARRY

SQL> SELECT * FROM SCOTT.testtable
WHERE c1 = TO_NUMBER(:1);

SELECT STATEMENT
TABLE ACCESS BY INDEX ROWID (TESTTABLE)
INDEX RANGE SCAN (TESTINDEX)

The answer is yes – just as Larry could have hinted his query to use the index, and it would have worked just as well (using the non-function-based part of the index), it works just the same if stored outlines are used instead. The use of stored outlines is compatible with indexes on function-based indexes and will not muck around with queries run by users who don’t have all the privileges on the functions used by those indexes.

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