RE: Does Oracle have a Sense of Humour?

wuff. That's not funny. That's the fact that optimizer never knows all the facts. Sometimes I would like Oracle to stop overoptimizing and revert to the old good rules approach...

BTW, it may be merely a bug. I found quite a good article on that issue:

Doc ID: Note:244040.1

Recommended Performance Patches
for Oracle E-Business Suite

https://metalink.oracle.com/metalink/plsql/f?p=130:14:4167759382313069588::::p14_database_id,p14_docid,p14_show_header,p14_show_help,p14_black_frame,p14_font:NOT,244040.1,1,1,1,helvetica

-----Original Message-----

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of jaromir nemec Sent: 7. júní 2006 08:34
To: oracle-l_at_freelists.org
Subject: Does Oracle have a Sense of Humour?

Hello,

I can't help posting this topic even it is not really a core theme of this list. I hope at least some may find this useful of just funny.

SQL> select * from t where d_id in (1111,1112,1113,1114,1115); . . . . .
9 rows selected.
Elapsed: 00:00:55.31

Well not really best response time, but wait there is an index on the table ...

SQL> select /*+ INDEX(t) */ * from t where d_id in (1111,1112,1113,1114,1115);
. . . .
9 rows selected.
Elapsed: 00:00:00.23

Excellent! But actually I need only one particular column of the table ...

SQL> select /*+ INDEX(t) */ x_id from t where d_id in (1111,1112,1113,1114,1115);
. . . .
9 rows selected.
Elapsed: 00:00:21.67

Upps!

The script to build the table is bellow. You can find more discussion under http://www.db-nemec.com/SenseofHumour.html In a OLTP configured DB you may need to add some members to the IN list to see the effect.

Regards,

Jaromir

• the script --- create table t (d_id number, x_id number, y number, pad char(100));
• stuff out histogram (with 255 different values)

insert into t
select
mod(rownum-1,255),
rownum, rownum,'x'
from dual
connect by level <= 5000000; --

• and fill the table with approx. 1 records per dim. key

insert into t
select
1000+trunc(DBMS_RANDOM.VALUE(0,1)* 5000000), rownum, rownum,'x'
from dual
connect by level <= 5000000;

--

commit;

--

create index t_idx on t(d_id);
create index t_idx2 on t(x_id,y,d_id);

--

begin
dbms_stats.gather_table_stats(ownname=>user, tabname=>'t',   method_opt=>'for all columns size 254', cascade => true,   estimate_percent => 10);
end;
/

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http://www.freelists.org/webpage/oracle-l Received on Wed Jun 07 2006 - 04:08:19 CDT