checkpoint
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Thread: checkpoint

  1. #1
    Join Date
    Jun 2002
    Posts
    62
    Does Checkpoint occur at log switch?
    Regards,
    Jack

  2. #2
    Join Date
    Sep 2001
    Location
    Düsseldorf, Germany.
    Posts
    588
    According to oracle checkpotints occures primiraily when (While database working normally)

    1. When a logswitch occures
    2. based on the parameter value LOG_CHECKPOINT_INTERVAL
    3. based on the parameter value LOG_CHECKPOINT_TIMEOUT


    HTH

    Sameer

  3. #3
    Join Date
    Jun 2000
    Location
    Madrid, Spain
    Posts
    7,447
    4. FAST_START_IO_TARGET
    5. LOG_FILE_SIZE

  4. #4
    Join Date
    Jun 2002
    Posts
    62
    Pando,

    Could you say a bit more abt LOG_FILE_SIZE? I read in Sybex book that checkpoint occurs when 90% of smallest logfile is full.
    Regards,
    Jack

  5. #5
    Join Date
    Jun 2000
    Location
    Madrid, Spain
    Posts
    7,447
    well incremental checkpoints is based on 2, 3, 4 and 5 we described, actually it is based on the minimum value of those 4 events

    if you look v$instance_recovery you will a couple of columns which says ACTUAL_REDO_BLKS and TARGET_REDO_BLKS and ACTUAL_REDO_BLKS is always less than TARGET_REDO_BLKS, when it is bigger checkpoints occurs, the TARGET_REDO_BLKS is the minimum of 4 events, if letīs say I have


    LOG_CHECKPOINT_INTERVAL very BIG say 1000000
    LOG_CHECKPOINT_TIMEOUT big as well such as 1800
    and
    FAST_START_IO_TARGET = 0

    then you will see different values in v$instance_recovery but the TARGET will be LOG_FILE_SIZE_REDO_BLKS since most probably (I am assumming here) it will have the smallest value compare with other 3 (well actually FAST_START_IO_TARGET will show NULL since itīs disabled by setting it to 0) and in this case incremental checkpoint will base its redo block address calculation on log file size. If you take this TARGET_REDO_BLKS value and do some calculation you will actually see it is 90% of the smallest redo log file size (here the Sybex book is taking about)

    If you mix three parameters (specially the time interval, I cant track it!) and the file size then itīs harder to track it by looking v$instance_recovery but at the end of the day it is Oracle that is doing the calculations




  6. #6
    Join Date
    Jun 2002
    Posts
    62
    Pando, thanks a lot for your promt response.
    Regards,
    Jack

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