Hi Niall,
IMO if the service is load balanced, the size of SGA do not depend on the
number of nodes.
Only when service distribution read very different data (buffer cache) or
run different code (shared pool) you may need to increase the SGA when
removing one node.
I've no confidence at all in the advisors. Use them only when people wants
me to give a number, it's still better than a random function...
Regards,
Franck.
On Thu, Oct 6, 2016 at 3:52 PM Niall Litchfield <niall.litchfield@xxxxxxxxx>
wrote:
A colleague asked me a question yesterday to which I don't really have a
good answer; so I thought I'd crowdsource it.
Given a RAC database of N instances each with an SGA of M gb in size. When
changing the instance count N how, if at all, do you modify the value of M?
What metrics do you look at, and what is the rationale behind that.
I'm aware that "let it run for a while and use the memory advisors" is an
approach - I can't say I have a lot of confidence in the memory advisors
from past experience.
--
Niall Litchfield
Oracle DBA
http://www.orawin.info
