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Oracle Tips by Burleson |
Oracle
and Bandwidth Saturation
A sub-optimal disk configuration can make even a
well-tuned Oracle RAC database slow to a crawl. An Oracle clustered
environment has multiple database instances all sharing the same set
of data files. MetaLink Note: 62172.1 notes that the top remedy for
increasing DBWRthroughput is
increasing the speed of the device.
This example from an AWR
report from $ORACLE_HOME/rdbms/admin/awrrpt.sqlshows an I/O bound database:
Top 5 Timed Events
~~~~~~~~~~~~~~~~~~ % Total
Event Waits Time (s) Ela Time
-------------------------- --------- ----------- --------
db file sequential read 2,598 7,146
48.54
db file scattered read 25,519 3,246
22.04
library cache load lock 673 1,363
9.26
CPU time 1,154 7.83
log file parallel write 19,157 837
5.68
Since most DBAs are too busy to run disk
performance scripts on every node of a large RAC cluster, they can
look to the web for examples of scripts. Another source is Mike Ault’s
book Oracle Disk I/O Tuning
(2004, Rampant TechPress), which also provides a plethora of scripts
and examples.
For the vast majority of non-scientific systems,
the primary bottleneck is disk I/O. Back in the days before RAID and
giant db_cache_size,
the DBA had to manually load balance the disk I/O sub-system to
relieve contention on the disks and the disk controllers. The next
section explores this topic.
The above book excerpt is from:
Oracle RAC & Tuning with
Solid State Disk
Expert Secrets for High
Performance Clustered Grid Computing
ISBN
0-9761573-5-7
Donald K. Burleson & Mike Ault
http://www.rampant-books.com/book_2005_2_rac_ssd_tuning.htm
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