Question: I want
to use two servers to failover to each other and I want to
size the servers such that the databases will work when a
failover occurs. What parameters do I need to set and
how do I manage a back-and-forth database failover. I
am using Data Guard physical standby.
Answer: The physical standby
database requires that both instances already exist on both
servers, so the SGA RAM is already allocated in case if
failover. If one of the servers failed and one of the
failover databases became a primary, you would see a spike
in CPU usage as new connections were directed to the new
instance. You might also see a PGA RAM shortage which
manifests itself as a spike in disk sorts and a decrease in
The most common error when DBA's set up a failover server
that is also an active database is that they forget to set
the OS parameter MAXUPROC to allow for the increase in
system processes. (This advice only applies to system
that use dedicated connections, and it does not apply to
system with connection pooling (shared servers, MTS)).
Normally, a DBA will make allowances for enough CPU to
support two instances and you can check the CPU runqueue
values as compared to the cpu_count. Remember, a
failover condition is rare and it does not make sense to
deliberately over-allocate server resources for an event
that is not likely to happen.
Today's servers have a Mean Time Between Failures (MTBF)
that is expressed in decades and a Mean Time To Recovery
(MTTR) that is expressed in hours, so the tradeoff is such
that a few hours of slow response time every ten years is
better than spending thousands of dollars in extra CPU's and
will not be used.
Oracle Training from Don Burleson
The best on site
training classes" are just a phone call away! You can get personalized Oracle training by Donald Burleson, right at your shop!
Burleson is the American Team
documentation was created as a support and Oracle training reference for use by our
DBA performance tuning consulting professionals.
Feel free to ask questions on our
considering using the services of an Oracle support expert should
independently investigate their credentials and experience, and not rely on
advertisements and self-proclaimed expertise. All legitimate Oracle experts
Oracle technology is changing and we
strive to update our BC Oracle support information. If you find an error
or have a suggestion for improving our content, we would appreciate your
and include the URL for the page.
Copyright © 1996 - 2016
All rights reserved by
is the registered trademark of Oracle Corporation.