Re: Oracle 8.1.7 can only use the first 15th indexes?

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Tue, 20 Jan 2004 23:19:25 -0800
Message-ID: <F001.005DDB11.20040120231925@fatcity.com>

drop table t1;

create table t1
nologging
pctfree 50
pctused 50
as select

 1 n01,
 1 n02,
 1 n03,
 1 n04,
 1 n05,
 1 n06,
 1 n07,
 1 n08,
 1 n09,
 1 n10,
 1 n11,
 1 n12,
 1 n13,
 1 n14,
 1 n15,

rownum n16,
lpad(rownum,10) v1
from all_objects
;

create index i01 on t1(n01);
create index i02 on t1(n02);
create index i03 on t1(n03);
create index i04 on t1(n04);
create index i05 on t1(n05);
create index i06 on t1(n06);
create index i07 on t1(n07);
create index i08 on t1(n08);
create index i09 on t1(n09);
create index i10 on t1(n10);
create index i11 on t1(n11);
create index i12 on t1(n12);
create index i13 on t1(n13);
create index i14 on t1(n14);
create index i15 on t1(n15);
create index i16 on t1(n16);

analyze table t1 estimate statistics;

set autotrace traceonly explain;

select v1 from t1 where n16 = 99;

set autotrace off

The execution path uses I16 on my system.

It would be possible to produced test cases that failed to use the 16th index, of course, and some of them could look quite convincingly as if the 16th index should be used. But it only takes one counter-example ...

(I assume the report intended to say the first 15 indexes on a specific table, 'cos the data dictionary alone has rather more than 15 indexes).

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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  who can answer the questions, but the
  person who can question the answers -- T. Schick Jr

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Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Wednesday, January 21, 2004 6:19 AM

> Hello again,
>
> I've just been reading a report for one of our systems and it says that
Oracle 8.1.7 will only use the first 15 indexes created. Any index created after the 15th will be ignored unless specified via a hint. Is this correct? I haven't heard of this before.
>
>
> TIA,
>
> Leng.
>
> ----------------------------------------------------------
> Leng Kaing
> Email: leng.kaing_at_team.telstra.com
> Phone: +61-3-9203-7589
> Mobile: +61-417-371-348
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Kaing, Leng
> INET: Leng.Kaing_at_team.telstra.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

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Received on Wed Jan 21 2004 - 01:19:25 CST