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Thread: just for the info sake.

  1. #11
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    dbafreak read Oracle Concepts, it's all explained there
    Go to index and search for instance recovery

  2. #12
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    The real why would and might be debatable but consider it as a THEOREM.

    No but ok here goes.....

    The first step of recovery from an instance or disk failure is to roll forward, or reapply all of the changes recorded in the redo log to the datafiles. Because rollback data is also recorded in the redo log, rolling forward also regenerates the corresponding rollback segments. This is called cache recovery.

    Rolling forward proceeds through as many redo log files as necessary to bring the database forward in time. Rolling forward usually includes online redo log files and may include archived redo log files.

    After roll forward, the data blocks contain all committed changes. They may also contain uncommitted changes that were either saved to the datafiles before the failure, or were recorded in the redo log and introduced during roll forward.


    Rollback segments record database actions that should be undone during certain database operations. In database recovery, rollback segments undo the effects of uncommitted transactions previously applied by the rolling forward phase.

    After the roll forward, any changes that were not committed must be undone. After redo log files have reapplied all changes made to the database, then the corresponding rollback segments are used. Rollback segments are used to identify and undo transactions that were never committed, yet were either saved to the datafiles before the failure, or were applied to the database during the roll forward. This process is called rolling back or transaction recovery.

    TARRY SAY: Thus the rolling bckwd first and forward later will defeat the purpose to attain transactional consistency.Something which is a matter of life and death by organizations.
    Tarry Singh
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  3. #13
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    Pando's right!
    The concepts is a very good read! A real eye opener.
    I read it every now and then to refresh my funda's(Fundamentals) during my exam preps..

    But it's good to have Q's like these coming up they prompt you to look into the book from the practical viewpoint.

    Tarry Singh
    Tarry Singh
    I'm a JOLE(JavaOracleLinuxEnthusiast)
    TarryBlogging
    --- Everything was meant to be---

  4. #14
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    Thanks for the explaination TARRY. I feel we are missing something here.

    When you said : "Thus the rolling bckwd first and forward later will defeat the purpose to attain transactional consistency.Something which is a matter of life and death by organizations"

    I didn't mean the "order" of the processes....I never questioned on the ordering.

    My fundamental question was "Why Rollback after Rollforward? Why not stop at the Rollforward point?? Why not retain the uncommitted data??"

    The very motive behind this interrogation is -- If uncommitted data was available before the failure, why not still retain the uncommitted after the recovery? Why rollback?? Why doesn't Oracle stop after Roll Forward??

    Hope I've made myself clear.

    Maybe I am missing something very trivial here. I would appreciate if TARRY or anyone can shed some light on this.

    Pando: I'm sure server concepts has a lot a knowledge in it (perhaps almost everything we discuss here). This is an interactive forum and makes it 100 times better than mere reading......my personal opinion.

    [Edited by dbafreak on 03-20-2002 at 12:24 AM]

  5. #15
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    the thing is what are explained is almost exactly same as ceoncepts guide, it wont take you more than 2 minutes go to technet, click con documentation link then click on 8i then concept guide then index and look for instance recovery

  6. #16
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    Originally posted by pando
    the thing is what are explained is almost exactly same as ceoncepts guide, it wont take you more than 2 minutes go to technet, click con documentation link then click on 8i then concept guide then index and look for instance recovery
    Sure Pando. As I menioned earlier, IMHO it makes a world of difference between "interacting" and "reading".

    Also -- "Interacting" saves time. For EXAMPLE -- Take the case of this very question I have asked in my previous reply to this post. Is there an easy way to find the answer in the concepts manual? NO! But here, there is; someone who has the knowledge will share it. Do you see any problems with my thinking here:-)

    Besides, I don't see any reason for you get uneasy about it. Its been a healthy and enjoyable discussion between me and TARRY. Take it easy Pando. There's lots more to it than we think.

    [Edited by dbafreak on 03-20-2002 at 03:08 AM]

  7. #17
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    what you are doing is ask for people look information for you.... I dont mind or care but I just see too many questions lately where people are just too lazy to just spend 5 minutes and find out themselves

    mind you, did you try to find out yourself before ask?

  8. #18
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    Originally posted by pando
    what you are doing is ask for people look information for you.... I dont mind or care but I just see too many questions lately where people are just too lazy to just spend 5 minutes and find out themselves

    It is still members' own choice. isn't it :-) C'mon Pando, I don't have to say this: No-one is asking anyone to go to concepts giude, do research and study and let the answer know. When we post questions here - we believe someone who knows the answer already will post the reply.

    Originally posted by pando
    mind you, did you try to find out yourself before ask? [/B]
    No. I didn't. Somehow I don't feel I should for this question. I have the liberty to ask, I ask. If someone knows the answer and feels like replying he will. If someone feels to go through the concepts manual, dig the answer and then reply - he still will. All these are individual interests. Why does it bother anyone like you in anyway....REALLY FAIL TO UNDERSTAND.

    Can someone please advise Pando to mind his own business!?!

    PS: Remember Pando, you are only a moderator for this forum. It doesn't qualify you to interfere in one's own interests. Besides, questions like I've posted only fosters for a better growth of the board. It will never disspiate adverse effects. Does anyone dis-agree with me (moderators?)

    [Edited by dbafreak on 03-20-2002 at 03:48 AM]

  9. #19
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    well if this is the way you use to learn the stuffs I am afraid itīs not the best if you rely on other people answering for you

  10. #20
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    Well dbafreak I think your fame will go before you then ... be yourself, I think is not a good idea to use others to answer things you don't want to find. All people will be bored of you quickly

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