If a log switch has not occurred for a long time and the database has not crashed, then there is little to worry about. If the database does crash, you really do not need to worry too much either since the transactions will be in the online redo logs. Even if a log switch does not occur, a checkpoint will occur frequently, forcing the DBWn process to write changed blocks back to disk.
If you committed your transaction and the instance fails, a record of your transaction will be in the online redo logs. A commit is not complete until the transaction and the commit are written to the online redo logs. When you start the instance, SMON will replay the transactions not yet written to disk and handle them appropriately.
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