rman 备份尽量使用 backup database plus archivelog
backup database archivelog all delete input; 当前日志不会切换及备份
RMAN archivelog backup
Yesterday I encountered a problem with a RMAN backup. There were no backups of archivelogs, only datafile backups and archivelogs. So I investigated the issue and found the following backup script:
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Looks good at the first glance but what it does is not what I wanted it to do. The “redundancy” is configured to be 1. So what happens is this, first the database is being backued up and right after it the archivelogs are being backed up to. But only those archivelogs that existed at the time the backup command started. No archivelogs that were created during the database backup are being backed up. So the archivelog backups become obsolete immediately and are deleted by the following “delete obsolete” command.
The thing is, the script should look like this:
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Minor change with a major impact.
Let’s see what happens in both cases
Case 1
Check what sequences are in the online logs and generate some more:
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At that point we have archivelogs until sequnce 18. Now we start the RMAN backup:
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We see, that all archivelogs until and including sequence 18 are being backed up. No sign of sequence 19 or any sequence beyond that.
Case 2
Again, we check the sequences in the online logs. There is no change to what we had ad the beginning of Case-1-Backup. That’s why I create some more archivelogs.
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Now we start the backup with the slightly modified command:
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Looks different now. We have a logswitch at the very beginning of the backup. Then all the archivelogs that exists at that point are being backed up. Then there is the database backup. And finally another logswitch is done and all the logs that were created during the database backup are being backed up too.
That is, what I really want.
Conclusion
The effect of the “plus archivelog” syntax is completely different from the combined “backup” command for different file types. So be very careful which option you use and most important: check your backup strategy by doing test restores on a regular basis.