Re: dictionary access via CBO without statistics

"Stephan Bressler" <stephan.bressler_at_siemens.com> wrote in message news:<b7lk8h$9s$1_at_news.mch.sbs.de>...
> I got 2 databases (8.1.7.4, solaris) on which accesses to dictionary objects
> (e.g. dba_extents) are made using cbo. I checked that no statistics are on
> any sys' tables and indexes using:
> select * from dba_tables where owner='SYS' and last_analyzed is not null
> select * from dba_indexes where owner='SYS' and last_analyzed is not
> null
>
> The execution plan shows costs and if a /*+ rule */ hint is used, the
> queries a much faster.
>
> optimizer_mode is choose.

I tested with set autotrace on and looked at v$sql. It always shows CHOOSE without COST information. I guess accessing data dictionary always shows CHOOSE unless it's hinted with /*+ rule */? Lack of COST may be a sign of rule-based, instead of cost-based. CHOOSE itself doesn't necessarily mean cost-based. If you see both CHOOSE and COST=somenumber, can you show your screen?

Yong Huang Received on Thu Apr 17 2003 - 11:59:03 CDT