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Thread: LMT for RBS?

  1. #1
    Join Date
    Sep 2001
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    Guys,

    Is there any advantage for using Locally Managed Tablespace for Rollback Segments?

    Thanks
    The Maverick
    Oracle Certified DBA - 8i

  2. #2
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    LMTs are the way forward! In Oracle9i they are the default:

    "When you do not explicitly specify the type of extent management for a permanent non-SYSTEM tablespace that you are creating, the default is locally managed."

    http://download-west.oracle.com/otnd...aces.htm#19132

    They certainly make life easier!

    The Oracle9i documentation implies that dictionary managed tablespaces will be deprecated in future versions. Can't find the quote at the moment.

    In addition, Automatic Free Space Management looks set to be the default in a future version. Once again, implied, not stated! No doubt freelists will be deprecated in Oracle12i
    Tim...
    OCP DBA 7.3, 8, 8i, 9i, 10g, 11g
    OCA PL/SQL Developer
    Oracle ACE Director
    My website: oracle-base.com
    My blog: oracle-base.com/blog

  3. #3
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    I've just re-read the question and realised I've not really answered it

    Yes, you should use them for RBS.

    If you use the uniform size option you will reduce the likelyhood of fragmentation if a segment expands and shrinks.

    The fact that they don't reference the dictionary for extent management means that the cost of expansions and shrinks is reduced. I'm not suggesting you size these segments incorrectly though.
    Tim...
    OCP DBA 7.3, 8, 8i, 9i, 10g, 11g
    OCA PL/SQL Developer
    Oracle ACE Director
    My website: oracle-base.com
    My blog: oracle-base.com/blog

  4. #4
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    Thanks for the advice Tim.

    using LMT for my RBS means that i cant specify storage parameters for my RBS right? but what if i get an error such as "SNAPSHOT TOO OLD" how can i resolve this? Can RBS on LMTs can prevent such an error?

    Thanks =)

    The Maverick
    Oracle Certified DBA - 8i

  5. #5
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    LMTs are not the answer. This error is caused because Oracle cannot maintain a read-consistency. You need to have bigger rollback segments, or have more of them:

    http://otn.oracle.com/docs/products/...cnsis.htm#2599

    Good luck!
    Tim...
    OCP DBA 7.3, 8, 8i, 9i, 10g, 11g
    OCA PL/SQL Developer
    Oracle ACE Director
    My website: oracle-base.com
    My blog: oracle-base.com/blog

  6. #6
    Join Date
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    Thanks again Tim!

    In conclusion, using LMT for my RBS gives Oracle the reponsibility of allocating and deallating of extents of rbs as well as managing the optimal size of my rbs right?
    and as long as i have enough rbs and rbs that is big enough i wont be encountering such problems like "SNAPSHOT TOO OLD" (Please correct me if im wrong)

    BTW, how can i set the SYSTEM TABLESPACE to LMT during CREATE DATABASE? what's the correct syntax of the command? i cant seem to find one =)

    Thanks !
    The Maverick
    Oracle Certified DBA - 8i

  7. #7
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    System tablespace cannot be LMT. It MUST be dictionary managed, same in Oracle 9i.
    Once you have eliminated all of the impossible,
    whatever remains however improbable,
    must be true.

  8. #8
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    Wink oracle commercial


    this reads like some crazy Oracle commercial.
    good stuff.

    - magnus

    "Enterprise? Why Enterprise?" <-- car rental commercial

  9. #9
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    if I remember right there are some bugs in 8.1.5 and 8.1.6 use LMT for RBS

  10. #10
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    Re: oracle commercial

    Originally posted by jgmagnus

    this reads like some crazy Oracle commercial.
    good stuff.

    - magnus

    "Enterprise? Why Enterprise?" <-- car rental commercial
    Come today and get not 1, not 2, but 3 extra extents per rollback segment!

    This offer is subject to age and status. Terms and conditions apply
    Tim...
    OCP DBA 7.3, 8, 8i, 9i, 10g, 11g
    OCA PL/SQL Developer
    Oracle ACE Director
    My website: oracle-base.com
    My blog: oracle-base.com/blog

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