VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 8

Quick I/O for Databases

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 file system 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

Caching for Quick I/O files can be enabled online when the database is running. You enable caching in two

steps:

Step 1. Set the qio_cache_enable parameter of vxtunefs to enable caching on a file system.

Step 2. Enable the Cached Quick I/O feature for specific files using the qioadmin command.

NOTE Quick I/O must be enabled on the file system for Cached Quick I/O to operate.

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.

You can make this setting persistent across mounts by adding a file system entry in the file

/etc/vx/tunefstab. For example:

/dev/vx/dsk/datadg/database01 qio_cache_enable=1

/dev/vx/dsk/datadg/database02 qio_cache_enable=1

For information on how to add tuning parameters, see the tunefstab (4) manual page.

Enabling Cached Quick I/O for Individual Files

There are several ways to enable caching for a Quick I/O file. Use the following syntax to enable caching on an

individual file: