Oracle 23c New Features for DBA'sMy old good friend has a question, am not sure whether I have cleared when we discussed but here I made this attempt.
“What is the difference between undo,flashback log, redo log files.”
First Flashback log vs. Redo log
1) Flashback logs and redo log files are similar in nature
2) LGWR writes to redo log files
3) RVWR writes to flashback logs
3) Redolog files are archived but flashback logs are reused
4) Flashback log file sizes are exactly or equal to the size of the redo buffer, unlike the redo log files (custom size)
5) Redo log files are used for rollforward the changes, but flashback logs are rollbacking the changes
6) * IMPORTANT * Flashbacklogs are alone not sufficient to do the flashback operation, redologs (archive) covering the flashback period must be available, since the previous images of the blocks contains in archives. (covering the whole time period between oldest_flashback_time column value and the time of failure)
Second, Flashback log vs. undo
1) Undo data is at transaction level
2) Flashback log covers the undo data at the block level
3) Undo does not record ddl operations where the flashback log does
4) UNDO data is used to backward changes at the transaction level while flashback logs are used to backward changes at the database level
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