need tips on dbwr_io_slaves ...
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Thread: need tips on dbwr_io_slaves ...

  1. #1
    Join Date
    Mar 2001
    Posts
    24

    Wink

    Hi.

    when I perform the following sql, it shows me lot of 'waits';

    here are the basic parameters and we are using unix on ibm (AIX)
    1G Memory and 4 CPU

    db_block_size = 8192
    db_block_buffers = 12000
    shared_pool_size = 46080000
    db_writer_processes = 2
    db_block_lru_latches = 2

    Would anyone agree to use dbwr_io_slaves instead? would the following helps?

    dbwr_io_slaves = 10
    db_writer_processes = 1


    Thx.

    ============================================
    OPS$MATTHEWC>
    1 select event, total_waits, average_wait from v$system_event
    2 where event in ('buffer busy wait', 'db file parallel write', 'write complete waits')
    OPS$MATTHEWC> /

    EVENT TOTAL_WAITS AVERAGE_WAIT
    ------------------------------ ----------- ------------
    db file parallel write 25324 250.058877

    1 row selected.

    OPS$MATTHEWC>
    ============================================

    db_block_size = 8192
    db_block_buffers = 12000
    shared_pool_size = 46080000
    db_writer_processes = 2
    db_block_lru_latches = 2
    matthewc

  2. #2
    Join Date
    Mar 2001
    Posts
    16
    Hello
    I don't think it's goona help because io_slaves are to share the work the got from the dbwr. instead more dbwrs are gonna help because they are gonna get and write directly. one dbwr is gonna pick up the same no of blocks at a time io_slaves are only to write that load faster.

  3. #3
    Join Date
    Apr 2000
    Location
    Edison, NJ
    Posts
    759
    You cannot use both dbwr_io_slaves and db_writer_processes. Which one to use depends on if your OS supports async or sync I/O, and which one performs better. Accordingly, you would set the appropriate value for the init.ora parameter, disk_async_io.

  4. #4
    Join Date
    Jan 2001
    Posts
    126
    Hi,

    AIX supports asynchronous IO. Configure sufficient AIO servers and run with disk_async_IO & one DB writer. It will give much better performance.

    Baliga

  5. #5
    Join Date
    Mar 2001
    Posts
    24
    Thx everyone.

    mbaliga. I have a question for U.
    How many db_block_lru_latches have U set for the 'one DB writer' ??
    Would it be better to give more lrulatches ??
    Thx
    matthewc

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