Understanding Buffered I/O and Direct I/O

The Essbase Kernel uses buffered I/O (input/output) by default, but direct I/O is available on the operating systems and file systems that Essbase supports, with the exception of Linux. See the Oracle Hyperion Enterprise Performance Management System Certification Matrix (http://www.oracle.com/technology/software/products/ias/files/fusion_certification.html).

Buffered I/O uses the file system buffer cache.

Direct I/O bypasses the file system buffer cache and is able to perform asynchronous, overlapped I/Os. The following benefits are provided:

If you set a database to use direct I/O, Essbase attempts to use direct I/O the next time the database is started. If direct I/O is not available on your platform when the database is started, Essbase uses buffered I/O, which is the default. However, Essbase will store the I/O access mode selection in the security file and attempts to use that I/O access mode each time the database is started.

Note:

Cache memory locking can only be used if direct I/O is used. You also must use direct I/O if you want to use an operating system's no-wait (asynchronous) I/O.