Oracle 参数 DBWR_IO_SLAVES 官方解释，作用，如何配置最优化建议

本站中文解释

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DBWR_IO_SLAVES参数控制数据库操作进程(DBWR)使用的文件I/O从进程数量。当系统出现磁盘I/O性能瓶颈，建议将该参数值设置大一点，以提高磁盘I/O的吞吐量。

默认情况下，DBWR_IO_SLAVES的值为0，表示不开启从进程，只有主进程。如果确实有I/O性能缓慢的情况出现，可以适当调整该参数。

正确设置DBWR_IO_SLAVES参数的方法是：

1、使用SQL或者SQL*Plus查看I/O使用的情况，比如可以使用V$SESSTAT和V$SYSSTAT视图，查看I/O操作的耗时和I/O调用次数；

2、如果耗时较高和调用次数较多，则适当调大DBWR_IO_SLAVES参数值，比如从0->2；

3、注意，调大DBWR_IO_SLAVES参数值有可能会降低系统性能，要根据实际情况来选择合适的值，并且需要经过一段时间的性能测试才能确定最佳参数值；

4、最终选择完成后，用alter system命令即可更新数据库参数。

官方英文解释

DBWR_IO_SLAVES specifies the number of I/O server processes used by the DBW0 process.

DBWR_IO_SLAVES is relevant only on systems with only one database writer process (DBW0). The DBW0 process and its server processes always write to disk. By default, the value is 0 and I/O server processes are not used.

If you set DBWR_IO_SLAVES to a nonzero value, the number of I/O server processes used by the ARCH and LGWR processes is set to 4. However, the number of I/O server processes used by Recovery Manager is set to 4 only if asynchronous I/O is disabled (either your platform does not support asynchronous I/O or disk_asynch_io is set to false).

Typically, I/O server processes are used to simulate asynchronous I/O on platforms that do not support asynchronous I/O or that implement it inefficiently. However, you can use I/O server processes even when asynchronous I/O is being used. In that case the I/O server processes will use asynchronous I/O.

I/O server processes are also useful in database environments with very large I/O throughput, even if asynchronous I/O is enabled.

See Also:

• “BACKUP_TAPE_IO_SLAVES”

• Oracle Database
  Performance Tuning Guide for more information about this parameter