Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

speeds up system reads by accessing the system buffer cache and avoiding disk
I/O when searching for information.
Having data at the cache level improves database performance in the following
ways:
■ For read operations, Cached Quick I/O caches database blocks in the system
buffer cache, which can reduce the number of physical I/O operations and
therefore improve read performance.
■ For write operations, Cached Quick I/O uses a direct-write, copy-behind
technique to preserve its buffer copy of the data. After the direct I/O is
scheduled and while it is waiting for the completion of the I/O, the file system
updates its buffer to reflect the changed data being written out. For online
transaction processing, Cached Quick I/O achieves better than raw device
performance in database throughput on large platforms with very large
physical memories.
■ For sequential table scans, Cached Quick I/O can significantly reduce the query
response time because of the read-ahead algorithm used by Veritas File System.
If a user needs to read the same range in the file while the data is still in cache,
the system is likely to return an immediate cache hit rather than scan for data
on the disk.
How to set up Cached Quick I/O
To set up and use Cached Quick I/O, you should do the following in the order in
which they are listed:
■ Enable Cached Quick I/O on the underlying file systems used for your database.
■ Exercise the system in your production environment to generate file I/O
statistics.
■ Collect the file I/O statistics while the files are in use.
■ Analyze the file I/O statistics to determine which files benefit from Cached
Quick I/O.
■ Disable Cached Quick I/O on files that do not benefit from caching.
Enabling Cached Quick I/O on a file system
Cached Quick I/O depends on Veritas Quick I/O running as an underlying system
enhancement in order to function correctly. Follow the procedures listed here to
ensure that you have the correct setup to use Cached Quick I/O successfully.
103Using Veritas Cached Quick I/O
Enabling Cached Quick I/O on a file system