Oracle 9i and Undo Segments Startup No#
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  1. #1
    Join Date
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    Oracle 9i and Undo Segments Startup No#

    Did a search prior to posting, ran across some older threads I didn't think needed resurfacing, so I'm posting a new one.

    I'm interested in discussing the way in which Oracle allocates initial and additional Undo segments. I've found on Metalink the following.

    Note: 135090.1 Managing Rollback/Undo Segments

    1. When creating an UNDO tablespace, these are automatically created:
    * n undo segments (based on SESSIONS parameter value)
    * named as _SYSSMUn$
    * owned by PUBLIC (usable for OPS configuration)
    * not manually manageable

    In the Oracle 9.2 documentation:

    When the instance starts up, it brings online a number of rollback segments as determined by either of the following:

    The ROLLBACK_SEGMENTS initialization parameter
    The TRANSACTIONS and TRANSACTIONS_PER_ROLLBACK_SEGMENT initialization parameters (Anyway, this only releates to PUBLIC rollabck segments anyway)

    I have the parameters

    SESSIONS = 170
    TRANSACTIONS = 187
    TRANSACTIONS_PER_ROLLBACK_SEGMENT = 5

    And yet 10 Rollback segments were onlined *scratches head*. I'm not sure how 9.2.0. arrived at on-lining 10 segments.

    Undo Segment 1 Onlined
    Undo Segment 2 Onlined
    Undo Segment 3 Onlined
    Undo Segment 4 Onlined
    Undo Segment 5 Onlined
    Undo Segment 6 Onlined
    Undo Segment 7 Onlined
    Undo Segment 8 Onlined
    Undo Segment 9 Onlined
    Undo Segment 10 Onlined


    Also, I found the followig information for when additional UNDO segments are onlined (Metalink: Rowena Serna)

    "It will online them as needed in this matter:
    * Any new txn created will attempt to bind to an undo segment with NO current active txns
    * When all online undo segments have active txns, then offlined undos will be onlined
    * If all offlined undo segs have been onlined, then more undo segs
    will be dynamically created.
    * When no more undo segs can be created (not enough space in the
    tablespace) then existing segments will allow multiple active
    txns "

    Any comments about the onlining of segments welcomed...

    Cheers,
    OCP 8i, 9i DBA
    Brisbane Australia

  2. #2
    Join Date
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    Re: Oracle 9i and Undo Segments Startup No#

    Originally posted by grjohnson

    And yet 10 Rollback segments were onlined *scratches head*. I'm not sure how 9.2.0. arrived at on-lining 10 segments.

    Undo Segment 1 Onlined
    Undo Segment 2 Onlined
    Undo Segment 3 Onlined
    Undo Segment 4 Onlined
    Undo Segment 5 Onlined
    Undo Segment 6 Onlined
    Undo Segment 7 Onlined
    Undo Segment 8 Onlined
    Undo Segment 9 Onlined
    Undo Segment 10 Onlined
    I think that initial creation of 10 undo segments is by default...
    It doesn't matter how big or small ur database is or what values you have set in
    SESSIONS = 170
    TRANSACTIONS = 187
    TRANSACTIONS_PER_ROLLBACK_SEGMENT = 5
    After the initial creation of 10 undo segments it proceeds further creation depending upon the values you mention in the init parameter file.

    Shout if i'm wrong
    Amar
    "There is a difference between knowing the path and walking the path."

    Amar's Blog  Get Firefox!

  3. #3
    Join Date
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    Re: Re: Oracle 9i and Undo Segments Startup No#

    Originally posted by adewri
    I think that initial creation of 10 undo segments is by default...

    Shout if i'm wrong
    defualt is 11
    funky...

    "I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."

    "Ego is the worst thing many have, try to overcome it & you will be the best, if not good, person on this earth"

  4. #4
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    ok, 10 + 1 for system....
    Amar
    "There is a difference between knowing the path and walking the path."

    Amar's Blog  Get Firefox!

  5. #5
    Join Date
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    Originally posted by adewri
    ok, 10 + 1 for system....
    thas correct.
    funky...

    "I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."

    "Ego is the worst thing many have, try to overcome it & you will be the best, if not good, person on this earth"

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