Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Quick I/O for Databases
Cached Quick I/O For Databases
Chapter 11 157
Cached Quick I/O For Databases
32-bit applications (such as 32-bit databases) can use a maximum of only 4 GB of memory because of the
32-bit address limitation. The Cached Quick I/O feature improves database performance on machines with
sufficient memory by also using the file system cache to store data.
For read operations through the Quick I/O interface, data is cached in the system buffer cache, so subsequent
reads of the same data can access this cached copy and avoid doing disk I/O. To maintain the correct data in
its buffer for write operations, Cached Quick I/O keeps the buffer cache in sync with the data written to disk.
With 64-bit applications, for which limited memory is not a critical problem, using the filesystem cache still
provides performance benefits by using the read-ahead functionality. Because of the read-ahead
functionality, sequential table scans will benefit the most from using Cached Quick I/O by significantly
reducing the query response time.
To use this feature, set the qio_cache_enable system parameter with the vxtunefs utility, and use the
qioadmin command to turn the per-file cache advisory on or off. See the vxtunefs(1M) and
qioadmin(1) man pages for more information.
Enabling Cached Quick I/O
You can enable caching for Quick I/O files online when the database is running as follows:
1. Set the qio_cache_enable parameter of vxtunefs to enable caching on a file system.
2. Enable the Cached Quick I/O feature for specific files using the qioadmin command.
NOTE You must enable Quick I/O on the file system to enable Cached Quick I/O.
Enabling Cached Quick I/O for File Systems
Caching is initially disabled on a file system. You enable Cached Quick I/O for a file system by setting the
qio_cache_enable option of the vxtunefs command after the file system is mounted. For example, to
enable Cached Quick I/O for the file system /database01, enter:
# vxtunefs -s -o qio_cache_enable=1 /database01
where /database01 is a VxFS file system containing the Quick I/O files.
NOTE This command enables caching for all the Quick I/O files on this file system.