OCI-61903
failed to allocate string bytes from shared pool for flashback generation buffer after string tries
Cause
An ALTER DATABASE FLASHBACK ON command is being issued while the database was open. The command failed because it could not get enough contiguous memory it needed.
Action
Restart the instance in mount mode and retry the command. An ALTER DATABASE FLASHBACK ON command should always be able to get enough contiguous memory when the instance is in mount mode.