(Re): Really Wierd Query tuning issue

From: ryan gaffuri <ryan.gaffuri_at_comcast.net>
Date: Thu, 12 Aug 2004 22:10:02 -0400
Message-ID: <009901c480da$a4e01030$350a5444@ryan2le36ofjce>

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_at_centrexcc.com> To: <oracle-l_at_freelists.org> 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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Received on Thu Aug 12 2004 - 21:05:47 CDT