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Thread: LRU List

  1. 09-12-2007, 05:24 AM #1
    malru
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    LRU List

    Hi,

    Given below is the Oracle saying Oracle Database buffer management,

    [The buffers in the cache are organized in two lists: the write list and the least recently used (LRU) list. The write list holds dirty buffers, which contain data that has been modified but has not yet been written to disk. The LRU list holds free buffers, pinned buffers, and dirty buffers that have not yet been moved to the write list. Free buffers do not contain any useful data and are available for use. Pinned buffers are currently being accessed.

    If the user process finds a dirty buffer as it searches the LRU list, it moves that buffer to the write list and continues to search. When the process finds a free buffer, it reads the data block from disk into the buffer and moves the buffer to the MRU end of the LRU list.

    If an Oracle user process searches the threshold limit of buffers without finding a free buffer, the process stops searching the LRU list and signals the DBW0 background process to write some of the dirty buffers to disk.]

    I have some doubts based on this,please clear it,

    1) Where the threshold limit for searching free buffers is set? How can i get value for this threshold limit?
    2) Is Write List nothing but MRU List?
    3) How long the pinned block will be in cache whether till the transaction completion or session completion?

    Thanks...
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  2. 09-12-2007, 11:37 AM #2
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    PAVB
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    lots of questions, huh?
    Let me pick up one of them.

    2- No, it is not. MRU stands for Most Recent Used (end of the LRU list).
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
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  3. 09-12-2007, 06:12 PM #3
    Sharma
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    #3. Pinned blocks are the blocks which are currently being read (they are only for the duration of time). Once the read is completed, they will move to MRU.
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  4. 09-13-2007, 02:16 AM #4
    hrishy
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    Hi

    1)The only person i know who can answer that question is Oracle and i think the algorithm for that changes between versions

    3)Its very dificult to tell how long it might stay there till you shut down the database also

    regards
    Hrishy
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  5. 09-13-2007, 04:55 AM #5
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    abhaysk
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    Quote Originally Posted by PAVB
    lots of questions, huh?
    Let me pick up one of them.

    2- No, it is not. MRU stands for Most Recent Used (end of the LRU list).
    pick easiest one.. ?
    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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  6. 09-13-2007, 07:15 AM #6
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    PAVB
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    Quote Originally Posted by abhaysk
    pick easiest one.. ?
    yup... you know, the early bird picks the easiest one
    Pablo (Paul) Berzukov

    Author of Understanding Database Administration available at amazon and other bookstores.

    Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
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  7. 09-13-2007, 07:18 AM #7
    hrishy
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    PAVB
    i thought that was the toughest question among all the three

    regards
    Hrishy
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