What's your db_file_multiblock_read_count set at, or are you using system stats? From the absence of cpu costs in the explain plan I'd say no. Without the index access, the order by requires a sort, which could put the cost of a "scan + sort" higher than the index access by unique index. A 10053 trace might be interesting and may help explain things, provided the two plans ARE actually different. At 08:10 PM 8/12/2004, you wrote: >I thought > >'set autotrace on' was already correct? It was just 'explain plan for' that >could be inaccurate? >I'll check the trace tomorrow. I think you are right about the full table >scan vs. the index scan. > >I did a unique scan and retrieved 1 record. The index is 1 block. So it >should be two LIOs. One to read the index block and 1 to read the record in >the table. Wierd that an 'order by' would coax oracle to do the right plan. > >The table fits inside one 1 MB extent. Any idea how to calculate how many >expected LIOs for a full table scan? If I do: >1 MB / 8192 block size I get 125, which is just about double my 63 LIOs? Regards Wolfgang Breitling Centrex Consulting Corporation http://www.centrexcc.com ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request@xxxxxxxxxxxxx put 'unsubscribe' in the subject line. -- Archives are at //www.freelists.org/archives/oracle-l/ FAQ is at //www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------