I had been following the thread "Varying plans on different nodes" (but may not have read all the emails in that thread) The question I quote below seems to have come up a few times :
Could you please explain how to get two sets of system stats in one database at a given time? AFAIK this is not possible because system stats are stored in a single table (sys.aux_stats$) and in it there is no mention of instance ID.
I would think that an RAC environment _CAN_ comprise of two dissimilar servers in terms of Hardware Resources -- CPU and Memory.In fact one of the premises of RAC is that you could run one service -- say "HR" --
on one node and another service -- say "Financials" -- on the other node, both sharing the same database. The idea being that the two services don't necessarily need the same Hardware Resources and do not have much Block Pinging but must share the same database. If so, youcould size a smaller server for the HR service and a larger one for the Financials service.
Wouldn't CPU (and even, quite possible, I/O response time as seen by the DB Instance -- the lighter instance makes fewer I/O calls and with OS buffering the I/O calls are possibly faster on this instance) be *different* on the two nodes ? The bean counters would want you to justify why you want 8 CPUs for the HR users who are a much lighter load . You might say "IF the Financials server goes down, we want the HR server to be able to take the load of the Financials Users". Management might say "IF the Financials server goes down, we reduce or stop the HR users and control the Financials users to only critical users / reports for the few hours it takes to bring up that server, but let's not waste 4 CPUs lying idle on the HR server for 3 years just because the Financials Server might go down for 2 to 4 hours once in those 3 years. RAC does give us *continuous* uptime , we do not HAVE to have *the same performance level* always -- we can afford reduced performance for 2 to 4 hours in 3 years as long as we still have 100% uptime. Let's just buy 4 CPUs for the HR server and 8 CPUs for the Financials Server." Wouldn't it be logical to have differently sized servers running different services even if in the same RAC Cluster ? Then wouldn't System Statistics be different between the instances ? Hemant K Chitale http://hemantoracledba.blogspot.com"First they ignore you, then they laugh at you, then they fight you, then you win" !" Mohandas Gandhi Quotes : http://www.brainyquote.com/quotes/authors/m/mohandas_gandhi.html