VERITAS Storage Foundation 4.1 Oracle Administrator's Guide

Chapter 14, Tuning for Performance
Prerelease 8 September 2005, 8:55am Tuning Oracle Databases
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Tuning Oracle Databases
To achieve optimal performance on your Oracle database, the database needs to be tuned to work
with VxFS. This section describes some of the Oracle parameters that you can tune to improve your
Oracle database performance when using Quick I/O.
Sequential Table Scans
Quick I/O performs all I/O as direct I/O. In the case of single-threaded sequential scans (common in
decision support system (DSS) workloads), using buffered reads can yield better performance.
Because the file system detects these sequential reads and performs read-aheads, the next few
blocks that Oracle requests are readily available in the system buffer cache and are simply copied to
the Oracle system global area (SGA). Because access from memory is inherently faster than access
from disk, this achieves a significant reduction in response time.
To handle large sequential scans when using Quick I/O, use the Oracle parallel query process to
break the single large scan into multiple smaller scans. This is done by setting the Oracle
parameters PARALLEL_MAX_SERVERS, PARALLEL_MIN_SERVERS, and
SORT_AREA_SIZE suitably.
Note Consult the Oracle documentation for your system and version of Oracle, and use the
settings recommended for these parameters when provided.
Asynchronous I/O
Quick I/O and Oracle Disk Manager support kernel asynchronous I/O, which reduces CPU
utilization and improves transaction throughput. Enabling the following parameters lets Oracle take
advantage of asynchronous I/O and avoids having to configure multiple DBWR slaves:
◆ If you are using Quick I/O datafiles with Oracle8i, set DISK_ASYNCH_IO to TRUE in
init.ora.
◆ If you are using ODM on Oracle9i, you do not need to change any init.ora parameters.
Your Oracle Installation Guide provides detailed instructions on implementing asynchronous I/O
on your system.
Tuning Buffer Cache
The UNIX buffer cache plays an important role in performance when using HFS or JFS in buffered
I/O mode. When using Quick I/O, however, the database cache must be tuned as if raw devices are
being used. You can allocate more memory to the database buffer cache because Quick I/O