3.1.2 Matrix Server Administration Guide

Chapter 7: Configure PSFS Filesystems 98

I/O buffering, allowing disk transfers to occur directly in application

buffers. In database server terms, this means the I/O will only be buffered

in the address space of the database server processes. For example, in the

case of Oracle9i, I/O will be buffered in the SGA or PGA. This eliminates

the “double-buffering” overhead associated with traditional filesystems.

Buffering directly in database server buffers also improves CPU

utilization because I/O buffers do not need to be copied from Kernel

space to database server buffers. Also, filesystem file data operations are

not serialized, allowing multiple reads and writes at the same time to the

same file from multiple processes. This allows applications to manage

their own file data coherency (e.g., databases) to operate more efficiently.

(The coherency of metadata, or structural, operations continues to be

managed by the PSFS filesystem.)

To take advantage of the DB Optimized performance optimization, an

application’s read or write buffer argument to the read or write system

call must be page-aligned and must be at least a multiple of 512 bytes in

length. Additionally, the target file address (the offset from the beginning

of the file where the I/O will start) must also be a multiple of 512 bytes. If

a transfer does not meet these three requirements, it will be slower.

Applications such as databases that support the use of raw partitions

always follow these constraints.

Unaligned I/Os from applications that support Database Operations are

still allowed, but will be slower. Examples of Database Operations

applications are tools used to back up, copy, and compress database files.

These tools may sometimes issue I/O operations that are not aligned

properly for this performance mount option, but will nonetheless operate

correctly.

The DB Optimized option controls only the way in which database files

are accessed for reads and writes; it does not affect the data itself. You can

switch between the Std. File Optimized and DB Optimized options when

mounting and then remounting a filesystem.

Uses for Filesystems Mounted with DB Optimized

Filesystems mounted with DB Optimized should be used only for

database objects (such as data files, transaction logs, the Oracle OCMS