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  1. #1
    Join Date
    Apr 2004
    Location
    zxczxczxc
    Posts
    52

    Unanswered: Cleaners During Check pointing

    Hi,
    I am running informix 9.30.FC2W8 on HP UX. I have allocated 50 Cleaners for 50 LRUS but During the Check point only 2 or 3 Cleaners are active. Can any body explain why is it so.


    Bye.
    zxczxczc

  2. #2
    Join Date
    Apr 2003
    Location
    Phoenix, AZ
    Posts
    177
    Depends upon how many dbspaces you have and how many dirty pages need to be written to different dbspaces. If all your dirty pages need to be written to only two or three dbspaces, that's all you will see active.
    Fred Prose

  3. #3
    Join Date
    May 2004
    Posts
    45
    pathri,

    At checkpoint time the page cleaners are assigned a chunk number to write dirty pages to. The cleaners will search all the lru queues for pages that belong to the chunk for that cleaner. Once the page cleaner has found all the pages for a chunk, the cleaners will write out the pages to the chunk.

    What is most likely happening is that a lot of your dirty pages belong to 2 or 3 chunks. If you want to get your other page cleaners involved in cleaning, check which tables the dirty row belong to and move those tables to another dbspace/chunk that is not hit during checkpoint time.
    Keith Brownlow
    ServerMetrics DB Monitoring (www.servermetrics.com)

  4. #4
    Join Date
    Apr 2004
    Location
    zxczxczxc
    Posts
    52

    Cleaners During Check pointing

    Hi,
    Thanks a lot for the information.

    Bye.
    zxczxczc

  5. #5
    Join Date
    Oct 2003
    Posts
    706
    As far as I know, no attempt is ever made to assign more than one cleaner to the same area, because of course all that will happen is that they'll conflict with each other and slow each other down with (pointless...) locking, unnecessary disk-seeks and what-not.

    The processes already employ asynchronous I/O, which means that they dispatch the disk-operation and continue without waiting for it to complete. So they run very efficiently.
    ChimneySweep(R): fast, automatic
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