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Oracle CPU Constrained Database
Oracle Tips by Burleson Consulting |
In Oracle, the
majority of wait time is spent waiting in I/O or performing
computations. As we have stressed, CPU enqueues can be
observed when the CPU run queue exceeds the number of CPUs on the
database server, and this can be seen by looking at the “r” column
in the
vmstat
UNIX/Linux utility or within the
Windows performance manager.
If the system is
already optimized, having CPU time as a top wait event is a positive
because the addition of faster CPUs or more CPUs will relieve the
bottleneck.
However, high CPU
usage is also indicative of excessive logical I/O (consistent
gets ) against the data buffers which might indicate the need
for SQL tuning or shared pool and library cache tuning. High CPU
usage will be reported as a top 5 timed even in any AWR report as
shown below:
Top 5
Timed Events
%
Total
Event Waits Time (s) Ela
Time
---------------------------------- ------------ -----------
--------
CPU
time 4,851 4,042 55.76
db
file sequential read 1,968 1,997
27.55
log
file sync 299,097 369 5.08
db
file scattered read 53,031 330
4.55
log
file parallel write 302,680 190 2.62
SEE CODE DEPOT FOR FULL SCRIPTS
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This is an excerpt from my latest book "Oracle
Tuning: The Definitive Reference".
You can buy it direct from the publisher for 30%-off and get
instant access to the code depot of Oracle tuning scripts: |
http://www.rampant-books.com/book_2005_1_awr_proactive_tuning.htm
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