Oracle Internals Notes

_filesystemio_options

The _filesystemio_options parameter was introduced in Oracle version 8.1.7 to control the use of program selectable direct I/O and asynchronous I/O against file system based database files. The following table shows the values that can be used when setting this parameter.

Buffered I/O Direct I/O

Synchronous I/O none directIO

Asynchronous I/O asynch setall

	Buffered I/O	Direct I/O
Synchronous I/O	`none`	`directIO`
Asynchronous I/O	`asynch`	`setall`

Databases that use a combination of say raw log files and raw tempfiles with file system based datafiles may wish to use kernelized asynchronous I/O against the raw files, but to avoid inefficient threaded asynchronous I/O against the datafiles. This can be done by allowing disk_asynch_io to default to TRUE, but setting _filesystemio_options to either none or directIO. Similarly, the parameter may need to be set to either directIO or setall to avoid buffered I/O against file systems that support direct I/O but do not provide a direct I/O mount option. The default value for this parameter is asynch, regardless of the disk_asynch_io parameter setting.