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6 Replies Latest reply: Nov 15, 2012 9:39 AM by vlethakula RSS

General Question for Learning

927578 Newbie
Currently Being Moderated
Hi,

Can anyone pls explain me.. When DBWR writes the data from DB Buffer Cache to Data Files ? what i'm thinking is if user COMMIT the transaction. is this right ? Pls Correct me if i'm wrong if possible pls explain me...
  • 1. Re: General Question for Learning
    sb92075 Guru
    Currently Being Moderated
    924575 wrote:
    Hi,

    Can anyone pls explain me.. When DBWR writes the data from DB Buffer Cache to Data Files ? what i'm thinking is if user COMMIT the transaction. is this right ? Pls Correct me if i'm wrong if possible pls explain me..
    what happens when session does DML that exceeds total RAM?

    when does datafile get changed?
  • 2. Re: General Question for Learning
    927578 Newbie
    Currently Being Moderated
    sb92075 wrote:
    924575 wrote:
    Hi,

    Can anyone pls explain me.. When DBWR writes the data from DB Buffer Cache to Data Files ? what i'm thinking is if user COMMIT the transaction. is this right ? Pls Correct me if i'm wrong if possible pls explain me..
    what happens when session does DML that exceeds total RAM?

    when does datafile get changed?
    Thanks for your question also ;).

    Can anyone pls answer this 3 question ? so that we can learn ?
  • 3. Re: General Question for Learning
    PavanKumar Guru
    Currently Being Moderated
    Hi,

    Please refer to Oracle docs
    http://docs.oracle.com/cd/E14072_01/server.112/e10713/process.htm#CNCPT1250
    http://docs.oracle.com/cd/E14072_01/server.112/e10820/bgprocesses.htm

    HTH

    - Pavan Kumar N
  • 4. Re: General Question for Learning
    jgarry Guru
    Currently Being Moderated
    You might find this informative, especially if you try it yourself: http://arup.blogspot.com/2010/12/100-things-you-probably-didnt-know.html
  • 5. Re: General Question for Learning
    vlethakula Expert
    Currently Being Moderated
    Your datafiles can contain uncomiited and commited data.

    When you issue a commit, message COMMIT COMPLETE would be displayed that means those changes are written to redolog files from log buffer cache(you are safe these changes are written from memory to files. As files are permanent storage)
    it is not necessary that those changes are written by dbwr from block buffer cache to datafiles;

    DBWR is lazy process ,it invokes
    upon checkpoint
    buffer cahce needs space
  • 6. Re: General Question for Learning
    927578 Newbie
    Currently Being Moderated
    vlethakula wrote:
    Your datafiles can contain uncomiited and commited data.

    When you issue a commit, message COMMIT COMPLETE would be displayed that means those changes are written to redolog files from log buffer cache(you are safe these changes are written from memory to files. As files are permanent storage)
    it is not necessary that those changes are written by dbwr from block buffer cache to datafiles;

    DBWR is lazy process ,it invokes
    upon checkpoint
    buffer cahce needs space
    Thank you vlethakula

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