Re: Parallel adaptive tuning!!

"Frank van Bortel" <frank.van.bortel_at_gmail.com> wrote in message news:dnudom$21k$1_at_news2.zwoll1.ov.home.nl...
>
> We do actually agree here,

        Glad to hear it - so please don't take
        the commentary below personally.
        This just happens to be a good point
        at which to air an opinion.

> but it's the choice of words:
> http://asktom.oracle.com/pls/ask/f?p=4950:8:11506770631431808713::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:8912905298920
>
> <quote>
> A hint "should be taken", if it is possible and sensible to take it
> </quote>
>
> So: a hint cannot be a directive (as you do acknowledge), as it can
> be out of context.
> Maybe I take the word directive too strong?
>

In principle I can agree that the problem is largely a choice of words and their meaning - but the word "hint" is a very bad choice, whereas the word "directive" is a much more accurate choice. If you can find a better word, I'll be happy to use it.

If you are not wearing any shoes, and I say to you

    Take off your shoes
Are you ignoring a hint, or unable to obey a meaningless directive ? The answer is pretty easy.

If I discover that you are driving to the local Kwik-E-Mart and say:

    When you drive down Thompson Street you must     take the 3rd right.
but your starting route doesn't take you anywhere near Thompson, are you ignoring a hint, or unable to obey a meaningless directive ? Slightly less obvious - because the sentence contains that implied instruction "Make sure your route takes you down Thompson Street" - but computers aren't really all that good at inferring what you meant to say.

My particular problem with the phrase "The optimizer can ignore hints" is that it should either be stated "your set of hints is incomplete" or "the optimizer cannot produce the execution path you want for that SQL statement". I don't approve of using hints casually - but when people decide to use them they need to know that they are not "hints" in the normal meaning of the word. Programmers are likely to spot when their hints are the equivalent of the shoes example - but they are less likely to spot the equivalent of the Thompson St. problem, so they should not be given the slightest opportunity to think that something isn't working because "it's only a hint".

-- 
Regards

Jonathan Lewis

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