VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Chapter 4, Using VERITAS Cached Quick I/O
Prerelease 8 September 2005, 8:54am Understanding Cached Quick I/O
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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 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.
Overview of How to Set Up Cached Quick I/O
To set up and use Cached Quick I/O:
1. Enable Cached Quick I/O on the underlying file systems used for your database.
2. Exercise the system in your production environment to generate file I/O statistics.
3. Collect the file I/O statistics while the files are in use.
4. Analyze the file I/O statistics to determine which files benefit from Cached Quick I/O.
5. Disable Cached Quick I/O on files that do not benefit from caching.
The rest of this chapter discusses how to set up Cached Quick I/O in more detail.