RAC 10g - Undo full istance off

Question

Hi,
I have Oracle Rac 10g environment with 2 istances in Solaris 10 SPARC.
For testing high availability, I have shutdown one istance and I have executed the performance test.
The undo datafile of instance off was filled, while the instance was running the other half, why?
Best Regards
Francesco Maisano

Answer 1

Hi Francesco,
Each instance in the RAC system can only use one undo tablespace at a time. In other words, instances cannot share undo tablespaces. Each instance in the cluster, being an independent transaction-processing environment, maintains its own UNDO area for undo management.
The undo tablespace cannot be shared among the instances at the same time. Only once an undo tablespace is released by an instance, it can be assigned to another instance. However, all instances can read blocks from any or all undo tablespaces for the purpose of constructing read-consistency images.
Switching Undo Tablespaces
You can switch from using one undo tablespace to another. Because the UNDO_TABLESPACE initialization parameter is a dynamic parameter, the ALTER SYSTEM SET statement can be used to assign a new undo tablespace.
If the parameter value for UNDO TABLESPACE is set to '' (two single quotes), then the current undo tablespace is switched out and the next available undo tablespace is switched in.
The database is online while the switch operation is performed, and user transactions can be executed while this command is being executed. When the switch operation completes successfully, all transactions started after the switch operation began are assigned to transaction tables in the new undo tablespace.
The switch operation does not wait for transactions in the old undo tablespace to commit. If there are any pending transactions in the old undo tablespace, the old undo tablespace enters into a PENDING OFFLINE mode (status). In this mode, existing transactions can continue to execute, but undo records for new user transactions cannot be stored in this undo tablespace.
An undo tablespace can exist in this PENDING OFFLINE mode, even after the switch operation completes successfully. A PENDING OFFLINE undo tablespace cannot be used by another instance, nor can it be dropped. Eventually, after all active transactions have committed, the undo tablespace automatically goes from the PENDING OFFLINE mode to the OFFLINE mode. From then on, the undo tablespace is available for other instances.
In another post I put the GV$ .. to you identify the cause of UNDO is full. (e.g Which transactions are on TBS UNDO full)
How undo Space Allocation Works
http://arjudba.blogspot.com/2008/04/how-undo-space-allocation-works.html
Regards,
Levi Pereira