(Re): Really Wierd Query tuning issue
- From: "ryan gaffuri" <ryan.gaffuri@xxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 12 Aug 2004 22:10:02 -0400
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?
----- Original Message -----
From: "Wolfgang Breitling" <breitliw@xxxxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, August 12, 2004 9:51 PM
Subject: Re: Really Wierd Query tuning issue
> Can you post the tkprof output from your sql trace or the trace itself.
> With bind variables you can not entirely trust the explain plan (even
> without you can not always). Could it be possible that the optimizer
> mistakenly chose a full scan for the query without the order by, which
> ended up using 63 LIO rather than the much fewer the optimizer expected.
> But with the order by, it DID use the index to save on the sort.
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