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Re: OCP Question (Perf Tuning)

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Tue, 06 Jan 2004 14:14:34 -0800
Message-ID: <F001.005DBE10.20040106141434@fatcity.com>

A bigger error in option (d) is that it leaves open the ambiguity of whether the rows
should, or should not, be part of the answer to the join.

Oracle's choice of join could be affected by adding 1000000 rows to the table that should be included in the join, but remain unchanged if you add 1000000 rows that
should not be included in the join.

Frankly it's an appallingly bad question, and I think your assumption about the wrong answer you are required to give is correct.

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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> Jonathan noted that
> > > Nope. The answer is b). In the FIRST_ROWS mode, optimizer
> > prefers NL
> > > to
> > all other
> > > methos despite the price.
> > >
> >
> > Unless the alternative is a full tablescan on the inner
> > table - in which case merge or hash joins can be
> > considered.
>
> For some reason hash joins were excluded from the question. I can't
> speculate as to what, other than oversight or limiting the answers to 4,
the
> reason for this might be.
>
>
> I suspect the answer *wanted* is b) the focus being that FIRST_ROWS
favours
> index scans and NL joins. ISTM that d) ought to be ruled out as it refers
to
> rows not blocks but as usual I am probably wrong.
>
> Niall
>

-- 
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 Tue Jan 06 2004 - 16:14:34 CST

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