Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

time that I/O spends on the disk, and the queueing time is how long it waits for
all of the other I/Os ahead of it. At the volume level or the file system level, there
is no queueing, so vxstat and qiostat do not show queueing time.
For example, if you send 100 I/Os at the same time and each takes 10 milliseconds,
the disk reports an average of 10 milliseconds of service and 490 milliseconds of
queueing time. The vxstat, odmstat, and qiostat report an average of 500
milliseconds service time.
About tuning Oracle databases
To achieve optimal performance on your Oracle database, the database needs to
be tuned to work with VxFS. There are a number of Oracle parameters that you
can tune to improve your Oracle database performance.
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 Oracle9, set DISK_ASYNCH_IOto TRUEin
init.ora.
Tuning for performance
About tuning Oracle databases
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