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Home -> Community -> Usenet -> c.d.o.server -> Re: Cache Hit Ratio from system views
>>>>>>>>
>>>>>>>> High BCHR is always better than low - provided everything else
>>>>>>>> being equal. If BCHR is useless for the stated reasons, no other
>>>>>>>> indicator would be useful.
>>>>>>>
>>>>>>> This I'm afraid is where you're fundamentally incorrect.
>>>>>>>
>>>>>>> A high BCHR can mean your database is on life support, struggling to
>>>>>>> cope with exessive LIOs due to inefficient SQL with users staring at
>>>>>>> an hourglass rather than returned data.
>>>>>>>
>>>>>>> A BCHR that has increased can mean your database has suddenly hit
>>>>>>> significant performance issues. Or it can mean things have improved.
>>>>>>> Or it can mean response times remain unaffected.
>>>>>>>
>>>>>>> A BCHR that has reduced can mean your database has suddenly hit
>>>>>>> significant performance issues. Or it can mean things have improved
>>>>>>> (yes, improved because that crippling transaction that was
>>>>>>> previously performing poorly due to massively exessive LIOs has been
>>>>>>> fixed, reducing the overall BCHR) . Or it can mean response times
>>>>>>> remain unaffected.
>>>>>>>
>>>>>>> Not much of an indicator is it ?
>>>>>>>
>>>>>>> But saying that a BCHR is *always* better than a low is just plain
>>>>>>> wrong wrong wrong ...
>>>>>>>
>>>>>>
>>>>>> Didn't I repeatedly say "provided everything else being equal"?
>>>>>>
>>>>>
>>>>> And how precisely do you determine that everything else indeed is
>>>>> equal ? Most databases don't exactly remain equal ...
>>>>>
>>>> >>>> No, they do not. That's why you do not look at BCHR alone, as I have >>>> said before. >>> >>> So what else do you look at in conjunction with the BCHR ? >>> >>> Interestingly, you never answer any of the questions and you never give >>> any examples of why you consider the BCHR to be such a fantastic >>> indicator. And yes, I have read *all* your contributions to this >>> discussion ... >>> >>> So how about you at least attempt to justify your claim that the BCHR is >>> "a very meaningful indicator". How do you actually use the BCHR in a >>> meaningful manner ? So you look at the BCHR and ..., and what ? >>> >>> And when do you look at these other "whatevers" in conjunction with the >>> BCHR ? When the BCHR increases, what else do you check ? And when the >>> BCHR decreases, what else do you check and how do these checks differ >>> from when the BCHR increases ? And when the BCHR remains the same, what >>> else do you check and how do these checks differ from when the BCHR >>> increases or decreases ? >>> >>> Remember, it's your claim that the BCHR is "a very meaningful >>> indicator", well show us ? >>> >>> If you can .... >>> >>>>
>>>> >>>> Try asking yourself the same questions about any other indicators you >>>> consider meaningful. The question here is not how to determine if >>>> everything else is equal. It is about whether BCHR means anything if >>>> everything else is equal. >>> >>> Please, if everything else is equal, how can the BCHR change ? How can a >>> high BCHR always be better than a low BCHR, everything being equal when >>> having a higher BCHR can only mean things are not equal by definition, >>> else the BCHR would be the same ? Right ? >>> >>> Can you please explain how this is possible, having a higher BCHR with >>> everything being equal, at least attempt some kinda description of what >>> "everything else" means, at least attempt to justify this somewhat >>> bizarre claim ... >>> >>> If you can ... >>> >>> Again I go back to my initial set of questions. If your BCHR were to >>> increase from (say) 95% to (say) 99.9%, if this very meaningful >>> indicator were to change in this manner, what else do you check to >>> ensure that things are really better, that the higher BCHR is actually a >>> good thing, that all these mysterious "things" are indeed equal ? >>> >>> And why wouldn't you need to check these other indicators when the BCHR >>> decreases ? >>> >>> And why wouldn't you need to check these things if the BCHR remains the >>> same ? >>> >>> If you can't answer these rather basic questions is a vaguely meaningful >>> manner, then ummmm, game over I think. >>> >>> Go on, answer these questions, dare ya !! >>> >>> If you can ... >>> >>> Cheers >>> >>> Richard >> > > Hey Bob, your best contribution to this whole discussion to date ... > > Cheers > > Richard
Coming from someone who can't read, I am not exactly flattered. Received on Thu Aug 30 2007 - 22:49:30 CDT
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