rollback_segments
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Thread: rollback_segments

  1. #1
    Join Date
    Apr 2001
    Posts
    151
    Hi all,

    I just noticed that no rollback_segment specified in my ini.ora file. Does that mean next time when db startup, all rollback_segment won't be online (execept system rbs)?
    I have startup DB several times already, and everytime rbs are all online. - confused now.

    thanks in advance
    Elin@trend

  2. #2
    Join Date
    Oct 2000
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    Dallas:TX:USA
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    if the rollback segments are PUBLIC then they will come online. Only for PRIVATE rollbacks you need to list them in the init file.

    - Rajeev
    Rajeev Suri

  3. #3
    Join Date
    Mar 2000
    Location
    CA
    Posts
    317
    When the RBS are created as default like now in 8 version RBS01 .. RBS20 are created by default, and if you are using the same, then you dont have to specify in your INIT.ora .

    Probably that's what is happening.
    Thanks
    Kishore Kumar

  4. #4
    Join Date
    Dec 2000
    Location
    Ljubljana, Slovenia
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    If you don't have any rollback segs specified in your init.ora, Oracle will calculate the number of RB segments it needs based on the following formula: number_of_RB_to_put_online = TRANSACTIONS/
    TRANSACTIONS_PER_ROLLBACK_SEGMENT. If you have this number of RB segments created it will bring all online. If you have more than this number of RB segments it will left the others in offline mode.
    Jurij Modic
    ASCII a stupid question, get a stupid ANSI
    24 hours in a day .... 24 beer in a case .... coincidence?

  5. #5
    Join Date
    Dec 2000
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    Ljubljana, Slovenia
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    Originally posted by rsuri
    if the rollback segments are PUBLIC then they will come online. Only for PRIVATE rollbacks you need to list them in the init file.
    AFAIK public and private RB segments are relevant only in Paralel Server environment. In normal configuration they behave exactly the same and the type of RB segment does not have any influence in the decision if system will bring the RB online or not.
    Jurij Modic
    ASCII a stupid question, get a stupid ANSI
    24 hours in a day .... 24 beer in a case .... coincidence?

  6. #6
    Join Date
    Apr 2001
    Posts
    151
    When rollblck_segments rbs_01 created,

    CREATE ROLLBACK SEGMENT rbs_01
    TABLESPACE
    STORAGE (INITIAL 10k NEXT 10k MINEXTENTS 2);

    how to make it public or priv. during creation of rbs

    20 rbs of my are public- if I don't specific when creating them, they are public. and acoording the formula, some will be online automatically. CORRECT!
    Elin@trend

  7. #7
    Join Date
    Feb 2001
    Posts
    203
    I am not sure about the formula, But when you are creating the rollback segments you have to specify the PUBLIC in
    create syntax,

    Other whys the rollback segment will be created as private.
    (On my knowledge).
    sree

  8. #8
    Join Date
    May 2001
    Location
    Delhi
    Posts
    341

    Rollbacks

    Hi Jmodic,

    You are saying that :

    If you don't have any rollback segs specified in your init.ora, Oracle will calculate the number of RB segments it needs based on the following formula: number_of_RB_to_put_online = TRANSACTIONS/
    TRANSACTIONS_PER_ROLLBACK_SEGMENT

    From where Oracle is going to get both the parameters.

    Pls. elaborate.
    --------------------------
    The Time has come ....

  9. #9
    Join Date
    Dec 2000
    Location
    Ljubljana, Slovenia
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    4,439
    Those are initialisation parameters. You might have them specified in the initSID.ora. If you don't specify them there oracle will assign some default values to them during startup. To check what values have been assigned to them in your instance, run the following:

    SELECT name, value FROM v$parameter
    WHERE UPPER(name) IN ('TRANSACTIONS', 'TRANSACTIONS_PER_ROLLBACK_SEGMENT');

    HTH,
    Jurij Modic
    ASCII a stupid question, get a stupid ANSI
    24 hours in a day .... 24 beer in a case .... coincidence?

  10. #10
    Join Date
    Mar 2000
    Location
    Chennai.Tamilnadu.India.
    Posts
    658

    Investigated

    Dear Jmodic, 10th May 2001 16:34 hrs chennai

    As you have said fine i queried the v$parameter it shows as follows.

    NAME VALUE
    ---------------------------------------------------------------- ------
    transactions 75
    transactions_per_rollback_segment 5

    So i should have 15 RBS ? but my query reads as follows

    SQL> select * from v$rollname;

    USN NAME
    ---------- ---------------------
    0 SYSTEM
    1 RBS0
    2 RBS1
    3 RBS2
    4 RBS3
    5 RBS4
    6 RBS5
    7 RBS6

    Note :In My init.ora RBS related parameters has been disabled.

    # If using private rollback segments, place lines of the following
    # form in each of your instance-specific init.ora files:
    #rollback_segments = ( RBS0, RBS1, RBS2, RBS3, RBS4, RBS5, RBS6 )

    # If using public rollback segments, define how many
    # rollback segments each instance will pick up, using the formula
    # # of rollback segments = transactions / transactions_per_rollback_segment
    # In this example each instance will grab 40/5 = 8
    # transactions = 40
    # transactions_per_rollback_segment = 5

    Cheers

    Padmam
    Attitude:Attack every problem with enthusiasam ...as if your survival depends upon it

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