Re: Mutating (SQL) execution plan!?...is that possible...stranges t thing I have every seen
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: john.kanagaraj@xxxxxxx
- Date: Thu, 10 Mar 2005 11:27:52 -0700
John Kanagaraj wrote:
> Chris,
>
>
>>>>I have the feeling you are setting yourself up for the=3D20 bind=20
>>>>variable peeking trap and appear to be falling into it.
>
>
> I am NOT a fan of using hidden parameters, but just be aware of the hidden
> parameter '_optim_peek_user_binds' (which is set to TRUE by default and
> enables bind peeking), that when set to FALSE in this case would take care
> of your "problem". Histograms *are* a useful tool when used appropriately,
> and can be a great help (and also a hindrance as you have seen).
>
While that is correct, you would already be at at least two layers of
band-aids. First using cursor_sharing=force to patch up the application
not using bind variables correctly ( being written in perl there is
really no excuse for that ) and then use an underscore parameter to
patch up the bind variable peeking trap because of the histogram created
by the broad "for all indexed columns ...". There are too many broad
assumptions at work here.
I hate to point it out because it could delay or avoid fixing the real
problem, but another possible workaround would be to use
cursor_sharing=similar - and that is at least a documented parameter.
--
Regards
Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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