!! Please do not post Off Topic to this List !!
Hi Christian,
Sorry, I'm not sure I share your opinion. CBO can decline hint only if the path is not
possible at
all.
It doesn't matter whether statistics exist or not. AFAIK that's the idea of hints.
As you can see earlier that path (N-L) is possible for the join.
Thanks,
Ed
> !! Please do not post Off Topic to this List !!
>
> Using hints don't force Oracle to use the path choosen
> when you write the query. Much more true in a join
> operation where Oracle has many choices. What you do
> is to restrict options. However Oracle have to look at
> the statistics for a final decision.
>
> Appart from what I said, are your statistics accurated
> ?. Try without aliases not only in the hint, also for
> the whole query. Are both tables indexed ?. Maybe is
> because of the cost of the unique scan of the index.
> The emp_id it is a sequence. If this is the case,
> maybe the clustering of the index is too high.
>
> Regards.
>
>
> --- "Shevtsov, Eduard" <[EMAIL PROTECTED]> wrote:
> > !! Please do not post Off Topic to this List !!Hi
> > List,
> >
> > did anybody notice that sometimes CBO ignores USE_NL
> > hint without ORDERED
> >
> > The following example was taken from oracle docs:
> >
> > SQL>
> > SQL>
> > SQL> select name, value
> > 2 from v$parameter
> > 3 where name = 'optimizer_mode';
> >
> > NAME
> > -----------------------------------
> > VALUE
> > -----------------------------------
> > optimizer_mode
> > CHOOSE
> >
> > SQL> desc employees
> > Name
> > --------------------
> > EMP_ID
> > MGR_ID
> > LAST_NAME
> > FIRST_NAME
> > HIREDATE
> > JOB
> > SALARY
> >
> > SQL> desc courses
> > Name
> > --------------------
> > CRS_ID
> > SHORT_NAME
> > DESCRIPTION
> > DAYS
> > DEV_ID
> > CAT_ID
> > LAST_UPDATE
> >
> > SQL> explain plan set statement_id = '37'
> > 2 for
> > 3 select /*+ ordered use_nl(e) */
> > 4 e.first_name
> > 5 , e.last_name
> > 6 , c.short_name
> > 7 from courses c, employees e
> > 8 where e.emp_id = c.dev_id
> > 9 ;
> >
> > Explained.
> >
> > SQL> @opt\explain_n
> > statement id: 37
> >
> > Query Plan
> > ------------------------------------------
> > SELECT STATEMENT Cost = 1022
> > NESTED LOOPS
> > TABLE ACCESS FULL COURSES
> > TABLE ACCESS BY INDEX ROWID EMPLOYEES
> > INDEX UNIQUE SCAN EMP_PK
> >
> > SQL> ed
> > Wrote file afiedt.buf
> >
> > 1 explain plan set statement_id = '38'
> > 2 for
> > 3 select /*+ use_nl(e) */
> > 4 e.first_name
> > 5 , e.last_name
> > 6 , c.short_name
> > 7 from courses c, employees e
> > 8* where e.emp_id = c.dev_id
> > SQL> /
> >
> > Explained.
> >
> > SQL> @opt\explain_n
> > statement id: 38
> >
> > Query Plan
> > -----------------------------------------
> > SELECT STATEMENT Cost = 84
> > HASH JOIN
> > TABLE ACCESS FULL COURSES
> > TABLE ACCESS FULL EMPLOYEES
> >
> >
> > QUESTION: why does the CBO ignore USE_NL without
> > ORDERED ?
> >
> >
> > Regards,
> > Ed
> > --
> > Please see the official ORACLE-L FAQ:
> > http://www.orafaq.com
> > --
> > Author: Shevtsov, Eduard
> > INET: [EMAIL PROTECTED]
> >
> > Fat City Network Services -- (858) 538-5051 FAX:
> > (858) 538-5051
> > San Diego, California -- Public Internet
> > access / Mailing Lists
> >
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>
> =====
> Eng. Christian Trassens
> Senior DBA
> Systems Engineer
> [EMAIL PROTECTED]
> [EMAIL PROTECTED]
> Phone : 541149816062
>
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> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Christian Trassens
> INET: [EMAIL PROTECTED]
>
> Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
> San Diego, California -- Public Internet access / Mailing Lists
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--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Shevtsov, Eduard
INET: [EMAIL PROTECTED]
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
San Diego, California -- Public Internet access / Mailing Lists
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