Confusion On Log_buffer Allocation
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Thread: Confusion On Log_buffer Allocation

  1. #1
    Join Date
    Feb 2005
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    3

    Question Confusion On Log_buffer Allocation

    Oracle 9.2.0.1 on AIX 5.3

    Most of my databases are very small. When the databases were 8.1.7 on AIX 4.3.3, I had determined that 76K was the smallest value that would be allocated for the log_buffers (even if I set it lower, I got 76K) and therefore that is what I set most of the databases to.

    Now that I have migrated to 9i on AIX 5.3, I notice that the log_buffer is actually showing 258K on these systems (via v$sgastat). Therefore, I assume that the 258K is now the minimum allocation for the new operating system.

    I then started playing with the values. If I set the log_buffer parm to anything <= 128K, I get 258K. From that point on, whatever value I set the log_buffer to, I actually get a value much larger that whatever I specified - usually about 130K-140K larger (130K gives 261K, 160K gives 300K 250K gives 388K)).

    Can anyone explain this?

    Thanks,
    Sheila

  2. #2
    Join Date
    May 2000
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    ATLANTA, GA, USA
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    Minimum log buffer size is platform dependent and also oracle release. It is quite natural you will see different values in different platforms.

    Tamil

  3. #3
    Join Date
    Feb 2005
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    3
    I was not really surprised to see the minimum size increase when we went to the new operating system - I knew that this value was very dependent on the OS.

    If I specify <= 128K, I get the apparent minimum of 256K (no problem here). What I am confused about is: If I specify anything > 128K, I actually get a value much larger (anywhere from 130K-140K larger).

    Why would the *real* value be this much larger than the specified parm?

    Sheila

  4. #4
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    What is the value set for log_parallelism?

    Tamil

  5. #5
    Join Date
    Feb 2005
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    3
    log_parallelism is defaulting to 1.

    Sheila

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