RE: Q about Oracle Optimizer

From: Mohammad Rafiq <rafiq9857_at_hotmail.com>
Date: Sat, 18 Aug 2001 06:34:13 -0700
Message-ID: <F001.003701A5.20010818064031@fatcity.com>

IMHO,Problem in this situation is that ,in 7.3.4 ,if I am not wrong ,thier optimizer must be RULE as default and after migration if optimizer is not explicitly set as RULE , default optimizer in 8.1.6 is CHOOSE. This is the reason their objects never analyzed in 7.3.4 or now in 8.1.6. If optimizer is set explicitly as RULE in initSID.ora will automatically resolve their problem...
Besides just going to CHOOSE and analyzing objects will not resolve all performance issues as it depends on application code, which was tuned/written keeping in mind RULE based optimizer and such codes must be checked and modified to get the best result under CHOOSE....

MOHAMMAD RAFIQ Reply-To: ORACLE-L_at_fatcity.com
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: Sat, 18 Aug 2001 05:45:19 -0800

That's true provided you're not using any of the new features introduced in 8.0, and later versions, that automatically cause the CBO to be used (e.g. partitioning, degree or instances > 1, IOT, etc...)

When in doubt, I always check metalink note: 66484.1.

HTH,

• Anita
  • Jon Walthour <jonw_at_fuse.net> wrote:
    > Volker:
    >
    > If optimizer_mode = 'choose', then the optimizer
    > chooses between
    > cost-based optimization and rule-based optimization
    > based on whether or
    > not statistics are present. In your case, since they
    > aren't it's using
    > rule-based.
    >
    > -----Original Message-----
    > Volker
    > Sent: Thursday, August 16, 2001 4:46 AM
    > To: Multiple recipients of list ORACLE-L
    >
    >
    > Hi list,
    >
    > a quick question about oracle optimizer.
    >
    > a customer has database migrated from 7.3.4 to 8.1.6
    > on AIX. Data was
    > transfered via full exp/imp. After migration the
    > performance of the new
    > database is very poor. I looked at the parameters
    > and saw that no object
    > is analyzed. So now me question:
    >
    > What does oracle optimizer do, if there are no
    > statistics on all
    > objects. Optimizer level is choose.
    >
    > Volker Schön
    > E-Mail: mailto:v.schoen_at_inplan.de
    > http://www.inplan.de
    >
    >
    > --
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    > INET: v.schoen_at_inplan.de
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Author: Mohammad Rafiq
  INET: rafiq9857_at_hotmail.com

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Received on Sat Aug 18 2001 - 08:34:13 CDT