Rollback Segment Usage 100%
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Thread: Rollback Segment Usage 100%

  1. #1
    Join Date
    Sep 2000
    Posts
    362
    Hi,
    From the Enterprise Manager I notoced that the usage of my rollback segment is 100%.

    Does this mean that I have to increase the rollback segment size ??

    Thanks
    Anurag

  2. #2
    Join Date
    Apr 2000
    Location
    Edison, NJ
    Posts
    759
    Check for rbs contention first.

  3. #3
    Join Date
    Jan 2001
    Posts
    126
    Hi,

    Set OPTIMAL value. This will shrink the rbs after use.

    Check for header waits as a % of total gets. If it is more than 1% you need more rollback segments.

    Baliga

  4. #4
    Join Date
    Feb 2001
    Posts
    49
    Hi

    If rollback contention is there, add some more rollback segment.

    Set the optsize for all the rollback segment.

    HTH
    I love dba job

  5. #5
    Join Date
    Sep 2000
    Posts
    362
    Hi,
    I see that there is no contention for the rollback segments.But I must tell you that there are 2 rollback segments having extent sizes of 56K each and having 348 and 330 extents respectively.

    I think such a high number of extents will have an impact on performance.

    What should I do do fix this and also how do I determine the optimal size of the rollback segments.

    I know that you have to set a low optimal value for small transactions and high for high transactions. But shouldnt I increase the rollback segment size and set the optimal to the current usage as thats the maximum it has been used.

    Please suggest.

    Thanks
    Anurag

  6. #6
    Join Date
    Apr 2000
    Location
    Edison, NJ
    Posts
    759
    Set optimal value to avg(hwmsize). Set the initial=next for the ts at half the optimal value. Extent allocation for rbs is CPU intensive, small extent size will affect performance/response time.

  7. #7
    Join Date
    Oct 2000
    Posts
    211
    Hi,
    check your transaction size. And assign 4 or 5 transacions per rollback segment. Say, your transaction is 50K. For 4 transactions, you need to assign an initial of 200k, make next also 200k and normally optimal is set to twice the initial.
    HTH
    manjunath

  8. #8
    Join Date
    Sep 2000
    Posts
    362
    Hi,
    How Do I calculate my transaction size and high water mark for the rollback segments. I am using Enterprise manager version 2.2 an it shows me the Used % and not the high water mark as it used to show in the previous versions.

    Thanks
    Anurag

  9. #9
    Join Date
    Apr 2000
    Location
    Edison, NJ
    Posts
    759
    Do a select hwmsize from v$rollstat

  10. #10
    Join Date
    Sep 2000
    Posts
    362
    Thanks everybody,

    Is there any specific reason for setting the optimal size at avg(hwmsize) . My optimal value comes out to be 20 MB. This means that my initial and next should be 10 MB each as opposed to the initial=next=56KB.

    what is the best approach to do this as it is not allowed to change the initial extent once it is set. Should I create 2 more rollback segments with the above values and bring them online and finally drop the older ones.

    Please suggest.

    Thanks
    Anurag

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