Re: adaptive cursor sharing and bind peeking

  • From: Mohamed Houri <mohamed.houri@xxxxxxxxx>
  • To: Christian Antognini <Christian.Antognini@xxxxxxxxxxxx>
  • Date: Tue, 4 Jun 2013 08:37:13 +0200

Thanks very much

2013/6/4 Christian Antognini <Christian.Antognini@xxxxxxxxxxxx>

> Hi Mohamed
>
> > May be I have not understood clearly the original poster question.
> > For me the question was whether the CBO (for cursors that are bind aware)
> > will always peek at the passed bind variable and optimize it or not?
>
> The OP never asked whether a re-optimization was performed. Instead, he
> wanted to know whether bind peeking was taking place. So, the "and optimize
> it" part was added by you.
>
> > This is why I answered that even if the cursor is bind aware the CBO
> will not
> > always use the passed bind variable to optimize a new plan (child
> cursor).
>
> This is true. Optimization is not done every time. But, bind peeking is
> done every time.
>
> > Instead it will share the plan that has been optimized for the bind
> variable having the
> > same "range of selectitivity" as the passed bind variable
>
> To estimate the range of selectivity and select the best child cursor bind
> peeking must take place.
>
>
> In summary: To me it seems you are implying that "bind peeking" =
> "re-optimization". However, these are two completely different
> functionalities. Bind peeking might take place even though a
> re-optimization is not performed.
>
>
> HTH
> Chris Antognini
>
> Troubleshooting Oracle Performance, Apress 2008
> http://top.antognini.ch
>
>
>


-- 
Bien Respectueusement
Mohamed Houri


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