Overheads of  Automatic SGA.

Hello
What are peformance overheads of turning on Automatic SGA(SGA_TARGET > 0 ) feature in 10gR2(10.2.0.3)? We are migrating our OLAP database to 10g on Linux and would like to know the impacts before we do that..
How frequently Oracle performs the resize operations and how much latencies it introduces to the response time?
How do you monitor the latencies introduced by SGA resize operations? i.e. what event user session will wait ( if waits ) if resize operations are under progress?
How buggy/stable this feature is ?

user4529833 wrote:
Hello
What are peformance overheads of turning on Automatic SGA(SGA_TARGET > 0 ) feature in 10gR2(10.2.0.3)? We are migrating our OLAP database to 10g on Linux and would like to know the impacts before we do that..
How frequently Oracle performs the resize operations and how much latencies it introduces to the response time?
How do you monitor the latencies introduced by SGA resize operations? i.e. what event user session will wait ( if waits ) if resize operations are under progress?
How buggy/stable this feature is ?As with all self-managing systems, there is an overhead. It is in two specific areas - monitoring and logging of the load and adjusting the parameters dynamically. You do pose an interesting question as to which metrics are available to monitor the management process. I have not dug into it, so I can not answer the question - yet. I'm just responding to highlight that it has an impact at other times as well.
Flip side - what are the performance overheads and performance losses associated with the DBA tuning (or, more likely not tuning) the SGA & PGA manually per the various workflow requirements. This is the case that the auto tuning was likely designed to tackle.
I highly doubt that the feature will be better than a crack DBA team adjusting the pools manually based on real and known workload. But I don't run into many situations where an entire crack DBA team can be assigned to proactively manage DB performance 24x7. (Thus, the feature becomes useful in spite of overhead.)

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