buffer cache hit ratio. LIO vs PIO - Page 4
DBAsupport.com Forums - Powered by vBulletin
Page 4 of 4 FirstFirst ... 234
Results 31 to 40 of 40

Thread: buffer cache hit ratio. LIO vs PIO

  1. #31
    Join Date
    Nov 2002
    Location
    Geneva Switzerland
    Posts
    3,142
    Originally posted by slimdave
    Ah that's true, but of all the statistics available I think that tuning the buffer cache hit ratio is the issue that has been unjustifiably force-fed down the throats of so many unwitting DBA's.
    So it's cheaper AND better to avoid these training courses

  2. #32
    Join Date
    Nov 2002
    Location
    Geneva Switzerland
    Posts
    3,142
    Originally posted by jodie
    Interestingly, v$db_cache_advice is available in 8i, but you can't turn cache advice on, so the important columns are empty!
    Thanks for that, I was doubting my sanity again.

    (Is that good marketing? Advertising the next release in the SYS.V$ views?)

  3. #33
    Join Date
    Sep 2001
    Location
    Ohio
    Posts
    334
    Originally posted by DaPi
    Thanks for that, I was doubting my sanity again.
    No Problem... I thought I was crazy, too! That's why I posted... to see if I was missing something.

  4. #34
    Join Date
    Dec 2002
    Location
    Bangalore ( India )
    Posts
    2,434
    Originally posted by slimdave
    Cache hit ratio is meaningless on it's own, right?
    bingo !!
    funky...

    "I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."

    "Ego is the worst thing many have, try to overcome it & you will be the best, if not good, person on this earth"

  5. #35
    Join Date
    Nov 2002
    Location
    Geneva Switzerland
    Posts
    3,142
    Originally posted by slimdave
    . . . . of all the statistics available I think that tuning the buffer cache hit ratio is the issue that has been unjustifiably force-fed down the throats of so many unwitting DBA's.
    I've been thinking about this, and I wonder if it is a result of students wanting "instant gratification" or a "silver bullet" or a "black or white answer". Or the teachers/writers finding it easier to give the answer.

    The logic might run:
    1) If you could only get one statistic from your db, which would you choose? I guess I would choose the hit ratio.
    2) So the hit ratio is the best.
    3) We want nothing but the best.
    4) We will only tune the hit ratio.

    (Obviously you get the same kind of nonsense if you choose another statistic.)

  6. #36
    Join Date
    Feb 2003
    Location
    Leeds, UK
    Posts
    367
    I've been thinking about this, and I wonder if it is a result of students wanting "instant gratification" or a "silver bullet" or a "black or white answer". Or the teachers/writers finding it easier to give the answer.
    I know what you mean. If you give people a set of metrics that should always be >= x on any type of Oracle database and this paves the way for "tricks and tips" on how to make sure you are hitting x or above and how you can ensure that you continue to do so. People like these kind of books and courses (and I admit I used to be one a couple of years ago). You think that for a small fee you will know everything you need to make any database run efficiently! Each new tuning book seems to be the same as the last e.g. a collection of "hot" SQL scripts, and a cottage industry in born. This seems to be changing now though, what with Milsap and Holt's new book. I reckon I've learnt more from reading that than I have from reading most of the big Oracle Press books combined!

  7. #37
    Join Date
    Oct 2002
    Posts
    182
    I went to Oracle Technology Day yesterday and throughout the whole seminar I kept hearing:

    "Check your cache hit ratio"
    "You can monitor your buffer cache hit ratio"
    "This allows you to easily tune your db according to your buffer cache hit ratio"

    Even Oracle tries to pound this into everyone's heads.
    Maybe they can't think of any other power words besides those ...
    - Cookies

  8. #38
    Join Date
    Jun 2000
    Location
    Madrid, Spain
    Posts
    7,448
    I will be glad if 10g's automatic tuning is based on hit ratio... will keep my job LOL

  9. #39
    Join Date
    Aug 2002
    Location
    Colorado Springs
    Posts
    5,253
    Originally posted by DaPi
    (Obviously you get the same kind of nonsense if you choose another statistic.)
    What if you chose volume of PIO's, or duration of PIO waits? I think I'd be happier with that.
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
    Washington, DC

    Oracle ACE

  10. #40
    Join Date
    Nov 2002
    Location
    Geneva Switzerland
    Posts
    3,142
    Originally posted by slimdave
    What if you chose volume of PIO's, or duration of PIO waits? I think I'd be happier with that.
    Yes, better - but still silly to focus on just one statistic.

    If you blindly minimise PIO you might end up back where we started with Millsap's LIO/PIO ratio of 99.99999999 . . . .
    I can't say I've ever seen that in my Oracle applications - but I did have a problem with Rdb under VMS: version 1 would thrash the disks for 5 minutes then the CPU would go to 100% and stay there for days (I'd cancel it on Monday morning); I could rewrite it as version 2, which would churn the disks for 30 minutes an then give the result (I think the optimiser was sensitive to litterary style!).
    I suspect that version 2 did more PIO, but I had neither the tools nor the expertise to prove it.

    There is no silver bullet. Over and out.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  



Click Here to Expand Forum to Full Width