What are active and inactive online redo log files?
What are active and inactive online redo log files?
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Log writer (LGWR) writes redo entries to online redo log files (groups) in a circular manner. The online redo log file that LGWR is currently writing to is called the current online redo log file. When the current online redo log file is full, a log switch occurs and LGWR starts writing to the next available online redo log file. When the last available online redo log file is full, LGWR returns to the first online redo log file and starts writing to it, starting the cycle again. A filled online redo log file is available to LGWR for reuse only after the online redo log file has been archived (if the database is running in ARCHIVELOG mode) and the corresponding checkpoint has been performed, i.e., changes recorded in the online redo log file have been written to data files.
Filled online redo log files that have not been archived and whose contents have not been written to data files are called active online redo log files, and they are required for instance recovery. On the other hand, filled online redo log files that have been archived and whose contents have been written to data files are called inactive online redo log files, and they are not required for instance recovery.
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