Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

For example, consider a system configured with 12GB of physical memory, an
operating system using 1GB, and a total Oracle size of 3.5GB. Unless you have
other applications running on your system, the remaining 7.5GB of memory is
unused. If you enable Cached Quick I/O, these remaining 7.5GB become available
for caching database files.
Note: You cannot allocate specific amounts of the available memory to Cached
Quick I/O. When enabled, Cached Quick I/O takes advantage of available memory.
Cached Quick I/O is not beneficial for all files in a database. Turning on caching
for all database files can degrade performance due to extra memory management
overhead (double buffer copying). You must use file I/O statistics to determine
which individual database files benefit from caching, and then enable or disable
Cached Quick I/O for individual files.
If you understand the applications that generate load on your database and how
this load changes at different times during the day, you can use Cached Quick I/O
to maximize performance. By enabling or disabling Cached Quick I/O on a per-file
basis at different times during the day, you are using Cached Quick I/O to
dynamically tune the performance of a database.
For example, files that store historical data are not generally used during normal
business hours in a transaction processing environment. Reports that make use
of this historical data are generally run during off-peak hours when interactive
database use is at a minimum. During normal business hours, you can disable
Cached Quick I/O for database files that store historical data in order to maximize
memory available to other user applications. Then, during off-peak hours, you
can enable Cached Quick I/O on the same files when they are used for report
generation. This will provide extra memory resources to the database server
without changing any database configuration parameters. Enabling file system
read-ahead in this manner and buffering read data can provide great performance
benefits, especially in large sequential scans.
You can automate the enabling and disabling of Cached Quick I/O on a per-file
basis using scripts, allowing the same job that produces reports to tune the file
system behavior and make the best use of system resources. You can specify
different sets of files for different jobs to maximize file system and database
performance.
How Cached Quick I/O improves database performance
Enabling Cached Quick I/O on suitable Quick I/O files improves database
performance by using the file system buffer cache to store data. This data storage
Using Veritas Cached Quick I/O
About Cached Quick I/O
102