Archive Generation in RAC environment.

Question

Gems,
I have one doubt it was not able to solve from my mind i.e.
As per my knowledge,
1) Every instance has its own thread so Thread is instance specific. My questions are, How the SCN will be maintained in ARCHIVES? will thread 1 & thread2 contains the same SCN?
2) If i have primary database with two nodes, and standby as single stand alone, How it will apply the archives on standby? I monitored ALERT log file of standby, Mostly it applies first thread 1 sequence, then thread2 sequence then thread1 sequence and then thread 2 sequence and so on.. Let me know if my assumption is wrong.
3) If i cloned from RAC to NON-RAC then, If in case if i performed SCN based recovery as
run
set until scn 10000;
restore database;
recover database;
then scn *10000* will contain in both the archives or only in one archives? or it contains only in one sequence? Please explain me.
Appriciated for the right answers, If you are unable to understand let me know, I will try to clear up more clearly.
Thanks

Answer 1

Hi,
first of all there are 2 kinds of SCNs. A "global" SCN and a local SCN per instance. Since 10g the SCNs are advanced with a mechanism called BoC (Broadcast on Commit).
Each time the LGWR writes to the redo log, LGWR sends a message to update the global SCN in all instances and to update the local SCN in all active instances.
1.) So each RedoLog entry knows the global SCN. So even though you have multiple instances, the SCN is unique (and in order).
2.) That depends on how the redlogs were written. If e.g. one instance did not write redologs for a while, it could be that 2 logs from instance 1 are needed before the log from instance 2 is needed. But in gerenall it will be "parts of redolog 1 then parts of redolog 2" etc.
3.) Yes you can, since the (global) SCNs are unique and will be used.
Regards
Sebastian