DB_WRITER_PROCESSES or DBWR_IO_SLAVES?
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Thread: DB_WRITER_PROCESSES or DBWR_IO_SLAVES?

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  1. #1
    Join Date
    Dec 2001
    Location
    Tel-Aviv,Israel
    Posts
    233

    DB_WRITER_PROCESSES or DBWR_IO_SLAVES?

    Hi folks,

    We have a very write intensive application (a lot of insert operations) and the most popular wait event we encountered is "free buffer wait".
    The parameter db_writer_processes was initially set to 4 (against 4 CPUs until yesterday).
    Actually,after some observations we made,we didn't see a difference between multiple DBWRs and one DBWR regarding the wait event "free buffer wait" and we still get a huge amount of
    this wait.
    Now the parameter db_writer_process = 1.

    What do you recommend from your experience : multiple DBWRs or working with io slaves (dbwr_io_slaves)?

    Following some details:
    Server - Linux 2.6.9-42.ELsmp i386 athlon
    CPUs - 8 (was increased yesterday from 4)
    Physical Memory (RAM) - 32GB
    Database version - 10.2.0.3.0

    Following the init*.ora parameters:

    Code:
    bilminer.__db_cache_size=956301312
    bilminer.__java_pool_size=16777216
    bilminer.__large_pool_size=16777216
    bilminer.__shared_pool_size=251658240
    bilminer.__streams_pool_size=0
    *.audit_file_dest='/b4bdb/app01/oracle/admin/bilminer/adump'
    *.background_dump_dest='/b4bdb/app01/oracle/admin/bilminer/bdump'
    *.compatible='10.2.0.3.0'
    *.control_files='/b4bdb/or01/bilminer/control01.ctl','/b4bdb/or02/bilminer/control02.ctl'
    *.core_dump_dest='/b4bdb/app01/oracle/admin/bilminer/cdump'
    *.db_block_checksum='FALSE'
    *.db_block_size=16384
    *.db_domain=''
    *.db_file_multiblock_read_count=64
    *.db_name='bilminer'
    *.db_writer_processes=1 # changed by roee 26/5/2007 was 4
    *.disk_asynch_io=FALSE
    *.dispatchers='(PROTOCOL=TCP) (SERVICE=bilminerXDB)'
    *.fast_start_parallel_rollback='FALSE'
    *.job_queue_processes=10
    *.log_archive_dest='/b4bdb/oa01/bilminer'
    *.log_archive_format='%t_%r_%s.arc'
    *.log_archive_max_processes=1
    *.open_cursors=500
    *.optimizer_index_caching=90
    *.optimizer_index_cost_adj=10
    *.pga_aggregate_target=827326464
    *.processes=2000
    *.remote_login_passwordfile='EXCLUSIVE'
    *.remote_os_authent=true
    *.sga_max_size=1258291200
    *.sga_target=1258291200
    *.undo_management='AUTO'
    *.undo_retention=21600
    *.undo_tablespace='UNDOTBS1'
    *.user_dump_dest='/b4bdb/app01/oracle/admin/bilminer/udump'
    *._optim_peek_user_binds=FALSE
    *.log_checkpoint_interval=999999999
    *.log_checkpoint_timeout=0
    Thanks in advance,
    Nir

  2. #2
    Join Date
    Jun 2000
    Location
    Madrid, Spain
    Posts
    7,447
    Hi

    If you are using Linux you can enable Asynch IO or Direct IO to achieve better write performance

    Also, isnt your db_file_multiblock_read_count too high?

  3. #3
    Join Date
    Dec 2001
    Location
    Tel-Aviv,Israel
    Posts
    233
    Hi pando,

    Thanks a lot for your advice!

    Regarding to DB_FILE_MULTIBLOCK_READ_COUNT - You are right.
    I'll check it tomorrow. This is an OLTP environment and not a DSS environment.
    Thanks for this remark also.

    Best regards,
    Nir

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