What are the changes in memory requirements from moving from single instance to RAC?
If you are keeping the workload requirements per instance the same, then about 10% more buffer cache and 15% more shared pool is needed. The additional memory requirement is due to data structures for coherency management. The values are heuristic and are mostly upper bounds. Actual esource usage can be monitored by querying current and maximum columns for the gcs resource/locks and ges resource/locks entries in V$RESOURCE_LIMIT. But in general, please take into consideration that memory requirements per instance are reduced when the same user population is distributed over multiple nodes.
