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ORA-01624:

log string needed for crash recovery of instance string (thread string)
Cause: A log cannot be dropped or cleared until the thread's checkpoint has advanced out of the log.
Action: If the database is not open, then open it. Crash recovery will advance the checkpoint. If the database is open force a global checkpoint. If the log is corrupted so that the database cannot be opened, it may be necessary to do incomplete recovery until cancel at this log.
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