Oracle RAC databases have more than one instance using the same set of resources, and a resource may be requested by more than one instance. Resource sharing is well managed by Global Cache Services (GCS) and Global Enqueue Services (GES). However, in some cases, the resource management operations could run into a deadlock situation and the entire database may hang because of serialization issues. Sometimes, software bugs also cause database-hang issues, and these situations almost always require the intervention of Oracle Support in the form of a service request.
Database-hang issues can be placed in the following categories:
Overall instance/database performance
Query performance ...