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  1. #1
    Join Date
    Nov 2004
    Posts
    143

    Question Unanswered: Long Checkpoints

    Hi,

    I am finding very long checkpoints in log file

    09:02:32 Checkpoint Completed: duration was 12 seconds.
    09:02:32 Checkpoint loguniq 393192, logpos 0xe61018
    09:06:20 Checkpoint Completed: duration was 8 seconds.
    09:06:20 Checkpoint loguniq 393197, logpos 0x10ce684
    09:07:41 Checkpoint Completed: duration was 5 seconds.
    09:07:41 Checkpoint loguniq 393199, logpos 0x1cc30a4
    09:12:02 Checkpoint Completed: duration was 8 seconds.
    09:12:02 Checkpoint loguniq 393202, logpos 0x159e5d0
    09:17:19 Checkpoint Completed: duration was 17 seconds.
    09:17:19 Checkpoint loguniq 393204, logpos 0x1455018
    09:22:26 Checkpoint Completed: duration was 3 seconds.
    09:22:26 Checkpoint loguniq 393206, logpos 0xc1a758
    09:27:38 Checkpoint Completed: duration was 8 seconds.
    09:27:38 Checkpoint loguniq 393208, logpos 0x92b4f0
    09:32:47 Checkpoint Completed: duration was 5 seconds.
    09:32:47 Checkpoint loguniq 393209, logpos 0x1349018
    09:37:55 Checkpoint Completed: duration was 2 seconds.
    09:37:55 Checkpoint loguniq 393211, logpos 0x5131c8
    09:42:17 Checkpoint Completed: duration was 12 seconds.
    09:42:17 Checkpoint loguniq 393211, logpos 0xd5b1b0
    09:44:17 Checkpoint Completed: duration was 10 seconds.
    09:44:17 Checkpoint loguniq 393211, logpos 0x15a315c
    09:45:51 Checkpoint Completed: duration was 9 seconds.
    09:45:51 Checkpoint loguniq 393212, logpos 0x8d534
    09:49:03 Checkpoint Completed: duration was 28 seconds.
    09:49:03 Checkpoint loguniq 393212, logpos 0x8de15c
    09:52:16 Checkpoint Completed: duration was 15 seconds.
    09:52:16 Checkpoint loguniq 393212, logpos 0x10f1018
    09:54:27 Checkpoint Completed: duration was 13 seconds.
    09:54:27 Checkpoint loguniq 393212, logpos 0x18d7484
    09:56:59 Checkpoint Completed: duration was 19 seconds.
    09:56:59 Checkpoint loguniq 393213, logpos 0x33560c
    09:59:47 Checkpoint Completed: duration was 20 seconds.
    09:59:47 Checkpoint loguniq 393213, logpos 0xc77038
    10:05:10 Checkpoint Completed: duration was 13 seconds.
    10:05:10 Checkpoint loguniq 393213, logpos 0x1010018

    Our onconfig parameters are
    LRUS 24 # Number of LRU queues
    LRU_MAX_DIRTY 25 # LRU percent dirty begin cleaning limit
    LRU_MIN_DIRTY 10 # LRU percent dirty end cleaning limit
    BUFFERS 80000
    CLEANERS 12

    We are running Informix Dynamic Server Version 7.31.FD5.

    This long checkpoints occurs normally when lot of users are logged in and also when some jobs are running during non business hours.

    Please suggest how to bring down the checkpoint duration.

    Thanks in advance.

    Nitin

  2. #2
    Join Date
    Apr 2003
    Location
    Phoenix, AZ
    Posts
    177
    First off, drop your LRU_MAX_DIRTY to 2 and LRU_MIN_DIRTY to 0. You want to start cleaning as soon as the buffers start to accumulate and never stop until you have no more to clean. Beyond that, you may have other issues such as where the logs files are located vs. the dbspaces.

    Also, all the dirty buffers may be for one dbspace?

    Your length between checkpoint seems to be a little (or a lot) too short. What's your checkpoint interval?
    Fred Prose

  3. #3
    Join Date
    Nov 2004
    Posts
    143
    Thanks Fred for replying. I will reduce the LRU_MAX_DIRTY and LRU_MIN_DIRTY. I have checked the activity on dbspaces. Disk read and writes are almost evenly distributed.
    How to identify the dirty buffers belong to which dbspace?
    My checkpoint interval is 300 secs.

  4. #4
    Join Date
    Jan 2005
    Posts
    30

    Smile identify the dirty buffers belong to which dbspace

    Use 'onstat -b' to identify the dirty buffers belong to which dbspace. Check the page address in the 'onstat -b' output. Page address are in 0xCCCPPPPP format; where CCC is chunk number and PPPPP is page offset to that chunk.

    Cheers!!
    Sanjit

  5. #5
    Join Date
    Nov 2004
    Posts
    143
    Hi Sanjit,

    I could not find page address in onstat -b output. There is pagenum in the output.

  6. #6
    Join Date
    Jan 2005
    Posts
    30

    pagenum & page address are same thing

    I’m sorry! It’s called pagenum in ‘onstat –b’ output. Though pagenum and page address both are same things.

    Sanjit

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