Re: Cache Hit Ratio from system views

On Aug 28, 2:42 pm, "Bob Jones" <em..._at_me.not> wrote:
> <fitzjarr..._at_cox.net> wrote in message
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> news:1188326738.313962.176280_at_19g2000hsx.googlegroups.com...
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> > On Aug 28, 12:14 pm, "Bob Jones" <em..._at_me.not> wrote:
> >> "Richard Foote" <richard.fo..._at_nospam.bigpond.com> wrote in message
>
> >>news:FyAAi.26736$4A1.1866_at_news-server.bigpond.net.au...
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> >> > "Bob Jones" <em..._at_me.not> wrote in message
> >> >news:eEnAi.234$ZA5.106_at_nlpi068.nbdc.sbc.com...
>
> >> >> "Richard Foote" <richard.fo..._at_nospam.bigpond.com> wrote in message
> >> >>news:OGWyi.24448$4A1.10071_at_news-server.bigpond.net.au...
> >> >>> "Bob Jones" <em..._at_me.not> wrote in message
> >> >>>news:aBuyi.50201$YL5.11519_at_newssvr29.news.prodigy.net...
>
> >> >>>> "Richard Foote" <richard.fo..._at_nospam.bigpond.com> wrote in message
> >> >>>>news:fgixi.22091$4A1.5979_at_news-server.bigpond.net.au...
>
> >> >>>>> "Bob Jones" <em..._at_me.not> wrote in message
> >> >>>>>news:eB8xi.1326$i75.244_at_newssvr19.news.prodigy.net...
> >> >>>>>>>> Why is BHCR meaningless? The answer should be short and simple.
> >> >>>>>>>> I
> >> >>>>>>>> want
> >> >>>>>>>> to hear your opinion.
>
> >> >>>>>>> One can not prove a negative.
> >> >>>>>>> Where is your proof BCHR is a reliable indicator of GOOD
> >> >>>>>>> performance?
>
> >> >>>>>> BCHR alone does not tell you about overall performance. It simply
> >> >>>>>> tell you the disk I/O percentage. It is an indicator, a very
> >> >>>>>> meaningful one.
>
> >> >>>>> If your "disk I/O percentage" is really really high, what does that
> >> >>>>> actually indicate ? Does it indicate all is well with the database
> >> >>>>> or
> >> >>>>> does it indicate all might not be well ? If you have SQL nasties
> >> >>>>> that
> >> >>>>> use index scans inappropriately or incorrectly loop through full
> >> >>>>> scans
> >> >>>>> of cached tables again and again and again, you might have users
> >> >>>>> experiencing extremely poor response times. Or you might have users
> >> >>>>> that are happy with their instant response times. You can't really
> >> >>>>> tell and so it doesn't really give you much of an indicator.
>
> >> >>>>> If your "disk I/O percentage" is really really low, what does that
> >> >>>>> actually indicate ? Does it indicate all is well with the database
> >> >>>>> or
> >> >>>>> does it indicate all might not be well ? It might indicate SQL
> >> >>>>> nasties
> >> >>>>> that use index scans inappropriately or incorrectly loop through
> >> >>>>> full
> >> >>>>> scans of tables (both large or small) and have users experiencing
> >> >>>>> extremely poor response times. Or you might have users that are
> >> >>>>> happy
> >> >>>>> with their instant response times as all their online transactions
> >> >>>>> run
> >> >>>>> instantaneously because the various large batch reports that are
> >> >>>>> running and causing all the high "disk I.O percentage" don't
> >> >>>>> directly
> >> >>>>> impact them at all. Just the BCHR ...
>
> >> >>>>> Sometimes when the BCHR changes from one level to another, it might
> >> >>>>> mean there's an issue. Sometimes it doesn't.
>
> >> >>>>> The one constant though is that when there are performance issues,
> >> >>>>> response times suffer for those folk/processes experiencing the
> >> >>>>> performance issues. That can happen if the BCHR is low or high. And
> >> >>>>> the actual cause of a performance issue needs to be investigated
> >> >>>>> whether the BCHR is high or low to determine an appropriate fix for
> >> >>>>> the issue.
>
> >> >>>>> Now if there are performance issues relating to excessive "disk I/O
> >> >>>>> percentage" bottlenecks for SQLs that are efficient either in terms
> >> >>>>> of
> >> >>>>> LIO counts or execution counts, then an increase in memory might be
> >> >>>>> a
> >> >>>>> reasonable cause of action. However, that requires looking at the
> >> >>>>> cause of the issue, not the possible symptoms.
>
> >> >>>>> Therefore the best indicator, the most meaningful one, is whether
> >> >>>>> response times are meeting business requirements or not. And if not
> >> >>>>> why not, regardless of the BCHR because a low or high BCHR may or
> >> >>>>> may
> >> >>>>> not be contributing to the problem. If response times do meet
> >> >>>>> business
> >> >>>>> requirements, then who really cares what the BCHR might be ?
>
> >> >>>> If that's the case, we don't really need to care about any
> >> >>>> indicator.
> >> >>>> Your argument is basically the same as others here. Please read my
> >> >>>> earlier postings.
>
> >> >>> Correct, we don't really need to care about any indicator that's as
> >> >>> ambigious as the BCHR.
>
> >> >>> However, response times is an idicator that isn't quite so ambigious
> >> >>> and
> >> >>> hence is something you should care about ...
>
> >> >> So you consider repsonse time a metric collected by system? Ok.
> >> >> What does 5 seconds response time tell you? What does 5 minutes
> >> >> response
> >> >> time tell you?
>
> >> > Are you seriously suggesting having a banking transaction resulting in
> >> > a
> >> > customer waiting for 5 minutes doesn't tell you anything about your
> >> > system
> >> > ?
>
> >> > Are you seriously suggesting that a BCHR that remains the same is a
> >> > better
> >> > and more "meaningful indicator" than a critical business response time
> >> > that varies from 5 seconds (telling me in answer to your question that
> >> > application users are happy) to 5 minutes (telling me users are not so
> >> > happy) ?
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> >> No, all I am suggesting is to go back and read the thread again. You will
> >> find yourself completely out of the loop.
>
> >> > Your "very meaningful indicator" hasn't budged at all (still sitting at
> >> > 99%) but the application has ground to halt ...
>
> >> > You remind me of someone who considered the health and well being of
> >> > the
> >> > Titanic to be based on the ratio of notes being played by the string
> >> > quartet, all things being equal !!
>
> >> Before trying to read my mind, please read the thread correctly first.
> >> Apparently some people here are debating with their ears blocked.- Hide
> >> quoted text -
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> >> - Show quoted text -
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> > One, anyway, named Bob Jones.
>
> > David Fitzjarrell
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> Mr. Fitzarrell, please tell me you are not older than 14. I will excuse you.- Hide quoted text -
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> - Show quoted text

I am much older than 14. You, however, debate like an 8-year-old. And I say that not to be rude, but to state the facts as I see them. You have been presented with evidence which negates your 'arguments' yet you persist in maintaining that your viewpoint is, basically, the only viewpoint worth considering. My six-year-old has presented more coherent arguments, sad to say.

David Fitzjarrell Received on Tue Aug 28 2007 - 14:47:46 CDT