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ORA-01581:

attempt to use rollback segment (string) new extent (string) which is being allocated
Cause: Undo generated to extend a rollback segment run out of current undo block space and is attempting to write into the new extent which has not been completely allocated.
Action: The rollback segment extending will be rollbacked by the system, no more extension will be possible untill the next extent is freed up by rolling back or committing other transactions.