RE: optimizer_ ???

  • From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
  • To: "Peter Alteheld" <palteheld@xxxxxxxx>
  • Date: Tue, 26 Apr 2005 10:56:00 +0200

Peter

>How huge can the impact on the response time be=20
>by tweaking oic? Precisely: do you know of an=20
>example where you gain a response time reduction=20
>which is very impressive?

Be careful... OIC has no direct impact on the
response time, it only has an impact on the=20
generation of an execution plan where joins are
involved. Therefore, it wont be a problem to=20
show you examples where:

- tweaking OIC led to catastrophic performance
- tweaking OIC had no impact on performance=20
- tweaking OIC led to excellent performance

But all this examples won't do nothing else that=20
demonstrate that in some specific cases OIC had=20
bad/no/good impact on performance.

What does this means? It simply means that you=20
should carefully analyze your system. If you=20
see that the CBO tends to inappropriately choose=20
too few or too many nested loops, it can be=20
beneficial to tune it.


HTH
Chris


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