Asynch I/O And DB_writer_processes

[st2000]

Environment: Oracle 8.1.7 on IBM RS/6000 AIX 4.3.3 (2 Processes)

I was reading on metalink that Synchronous IO does not work on Filesystems (atleast HP) and only on raw disks and alternate to that is to have Asynchronous I/O or having multiple db_writer_processes. I also read that db_writer_processes > 1 along with Asynch I/O will not work fine together.Today I changed my db_writer_processes to 2 from 1, and I can see that few batch jobs went screaming low by 30mts vs 2-3 hrs. Should I shut off my asynchronous I/O then? Am I risking anything? Is it true that Asynch I/O works better on Raw disks compared to Filesystems?

Thanks, ST2000

[Calvin_Qiu]

Wrong, in most of Unix system, such as Solaris, Asynchronous I/O does not work on file systems and only on raw devices. You can enable Asynchronous I/O or configure DBWR_WRITER_PROCESSES or DBWR_IO_SLAVE to simulate Asynchronous I/O. If you use the DBWR_IO_SLAVE parameter, only one DBWR process is used, regardless of the setting of the DBWR_WRITER_PROCESSES parameter.

AIX versions 4 and higher support Asynchronous I/O (AIO) for database files created both on file system partitions and on raw devices.

Please refer to Oracle 9i R2 Administrator's Reference for Unix for more information.