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Thread: Rollback Segment

  1. #1
    Join Date
    Nov 2000
    Posts
    157
    Hi Guys,

    I have a question on rollback segments.I hope so many of you are good enough to clarify this.Please give me a detail reply.I read some books but unfortunately I think i am not getting the core concept.

    I have a production database 24*7 (Oracle 734 on Windows NT 4.0 Patch 6a).I created another database on the same server whoose structure is as same as production(empty database) for some purposes.In production database i have 10 rbs EACH OF 1M AND ROLLBACK TABLESPACE IS 30M.But in the empty database :

    I created a tablespace :

    create tablespace rollback
    datafile '/rollback' size 500m autoextend on next 1m
    default storage (initial 160k,next 160k,minextents 1,maxextents unlimited,pctincrease 50);

    I created a rollback segment

    create rollback segment rbs2
    tablespace rollback
    storage(initial 30m,next 30m,minextents 2,maxextents 121);

    1.When i see from OEM the used space in rollback tablespace is 60m .Is it because of 2 minextents each of 30m?

    2.Is it good enough to cretae a one big rollback segment instead of few smaller ones?

    3.If not ,how many small RBS i have to create with what parameters cosidering my rollback tablespace.

    Thanks in advance
    Ravi

    ravi

  2. #2
    Join Date
    Mar 2001
    Posts
    45

    Exclamation

    1. Yes, Rollback segments should possess minimum 2 extents (Oracle recommends like that). that is the reason for 60M.

    2. It is always advisable to have 1 rollback segment for every four user transactions. So have more than 4 RBS atleast and if you feel ur env. may have long running bulk batch jobs, have one big RBS. Which you can particularly devote for thos jobs.

    3.Refer Rollback segment config. & tips - available in
    Oracle Metalink in detail.

    ---


    Thanx
    Ramesh.
    ______________________________
    There is nothing Impossible.
    Even Impossible says
    I M POSSIBLE

  3. #3
    Join Date
    Oct 2000
    Location
    Saskatoon, SK, Canada
    Posts
    3,925
    Befor eanswering to your questions, I'ld assume that you know the purpose of using the RBS. If not, I'ld suggest that you go through the following thread

    [url]http://www.dbasupport.com/forums/showthread.php?threadid=7838[/url]

    These would answer some of the other questions:

    [url]http://www.dbasupport.com/forums/showthread.php?threadid=7506[/url]

    Now on answering to some of the other questions; yes, you see the initial extent size of 30M and if the extents were to go up then you would see that total size on OEM.

    Though RBS can have concurrent user information, if the instance were to fail, then oracle would have to retrive the information from the RBS. But is depends on your shop. It is oracle's recomedation that you have a number of small RBS for the OLTP applications, since they perform small number of inserts, updates and deletes.

    I would always have minimum of 10 RBS.

    Sam
    Thanx
    Sam



    Life is a journey, not a destination!


  4. #4
    Join Date
    Nov 2000
    Posts
    157
    Thanks for your help and advices.

    Ravi
    ravi

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