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DB_WRITER_PROCESSES

原创 Linux操作系统 作者:mambo_shen 时间:2010-07-30 14:01:27 0 删除 编辑

DB_WRITER_PROCESSES = 2 * number of CPU cores

IO快到有空置的時間, 那麼加dbwr便有作用了
Multiple DBWR processes is preferred over the use of I/O slaves. I/O slaves should only be used if multiple DBWR processes cannot be configured.
It is DBWR’s responsibility to make free buffers available by writing modified blocks to the datafiles.

SELECT   event,
           total_waits,
           time_waited,
           average_wait
    FROM   v$system_event
   WHERE      event LIKE 'db file %'
           OR event = 'free buffer waits'
           OR event = 'write complete waits'
ORDER BY   time_waited DESC
/

                                 TOTAL    TIME   AVG
EVENT                    WAITS  WAITED  WAIT
----------------------- ------ ------- -----
free buffer waits       194278 4488038 23.10
db file sequential read 588805 2900049  4.93
db file parallel write   34667  119035  3.43
db file scattered read   19283   10242  0.53
write complete waits       175    5481 31.32
db file single write       378    1261  3.34

Firstly, the operating system and database instance must be configured to make non-blocking I/O (asynchronous I/O) available to DBWR.
Secondly, the datafiles must be spread over enough disks, controllers and I/O busses to ensure that there are no hot spots in the I/O subsystem.
This I/O tuning typically involves the use of striping, and commonly involves the use of raw datafiles also.

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