Rollback to Undo in a RAC env. 2004-08-13 - By Daniel W. Fink
Interesting question. The docs don 't seem to address this particular
question. According to the RAC parameter section, UNDO_MANAGEMENT is not
required to be identical amongst all instances. Since each instance must
have their own undo segments (in AUM the undo tablespace), I would
theorize that it is possible to have the instances running in separate
modes. I would be concerned about 2 things (at least). First, how will
the auto undo instance perform read consistency with entries from a
manual rollback segment (of course, I 've never tested cr in a RAC
environment)? Second, what are the recovery implications?
In terms of known problems, avoid automatic undo in a high transaction
volume OLTP system. The basic process of UNDO generation and application
has not really changed, so you should not see performance problems. In
all the testing I have done or been exposed to, performance was never an
issue that could be tied to one type of undo management versus the other.
Regards,
Daniel
GUPTA, DEEPENDER wrote:
>Hi All,
>
>I am planning to covert the undo management from MANUAL to AUTO in a RAC
>environment with 2 nodes.
>
>My question is, do I need to shutdown both the instances for doing this or
>can I change this parameter for 1 instance at a time. Can oracle mount 2
>different instances with different UNDO management at a given point of time?
>
>Last time when I upgraded the compatible parameter to 9200 I tried it one by
>one first and I got the error message ORA-1105 (See ORA-1105.ora-code.com) as one instance was mounted
>with compatible parameter 817 and I was trying to mount the other one with
>compatible parameter 9200.
>
>Also pls advise if any type of performance problems has been observed with
>AUM.
>
>Regards
>
>
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