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Home -> Community -> Usenet -> c.d.o.server -> Re: ANALYZE Command
Just Visting wrote:
>
> In the past the cost based optimizer made some REAL BAD "choices".
> At which revision level of Oracle would you be 95% confident that the
> statement below is true & reliable?
>
> For which versions (older than 7.x.y.z?) would the rule-based
> optimizer typically yield better results than the cost optimizer?
> ======================================================
> On Fri, 02 Jul 1999 08:29:04 -0400, Kenneth C Stahl
> <BluesSax_at_Unforgettable.com> wrote:
>
> >The whole purpose of ANALYST TABLE ..... COMPUTE STATISTICS; is to provide
> >the programmer with information (although it is possible to glean
> >interesting information from the statistics columns). The purpose is to make
> >cost-based optimization work properly. Without the statistics all of your
> >sql will be optimized by the rule-based optimizer and that means that you
> >must be careful to tune the sql yourself and may necessitate multiple
> >attempts as you run the statement through EXPLAIN to look at the execution
> >path. Once you run statistics the cost-based optimizer will automatically
> >rearrange your sql to use the most efficient execution path within the scope
> >of the methods used by the cost-based optimizer. The cost-based optimizer
> >may still get things done the most optimal way possible because it can
> >select the wrong index or do other things that introduce inefficiencies into
> >the execution, but for most cases it will do the optimization better than
> >you can do it by hand.
> >
> >Ken
> >
> >Connor McDonald wrote:
> >
> >> flowerss_at_my-deja.com wrote:
> >> >
> >> > I've just started performance tuning a database
> >> > and I don't understand the logic of the ANALYZE
> >> > command. I ran the command; however, I don't
> >> > understand how to make use of it. Specifically,
> >> > the Endpoint_Number and Endpoint_Value Field?
> >>
> >
We decided that the cost method started paying dividends from 7.3.3 onwards...You still get the occasional SQL that needs some hints but on the whole, the optimiser decisions are sound --
"Some days you're the pigeon, and some days you're the statue." Received on Sat Jul 03 1999 - 04:59:53 CDT
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