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| Re: Archivelog backup and Incremental backup [message #685320 is a reply to message #685318] |
Wed, 08 December 2021 06:22   |
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Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille
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Senior Member
Account Moderator |
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Quoting the doc.
Quote:To back up the database while it is open, or to be able to perform complete or point-in-time media recovery, you must enable the archiving of redo log files.
Information in the redo log files are "archived" into the archived log files. Kind of transactional log.
So, as long as you need an online backup , you need the archived logs too.
Quote:
A database backup, together with online and archived redo log files, guarantees that you can recover all committed transactions in the event of an operating system or disk failure.
If you keep an archived log, you can use a backup taken while the database is open and in normal system use.
You can keep a standby database current with its original database by continuously applying the original archived redo logs to the standby.
[Updated on: Wed, 08 December 2021 06:29] Report message to a moderator |
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| Re: Archivelog backup and Incremental backup [message #685324 is a reply to message #685318] |
Wed, 08 December 2021 09:02 |
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EdStevens
Messages: 1376
Registered: September 2013
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Senior Member |
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BalajiDBA wrote on Tue, 07 December 2021 22:57Hi,
Could someone please explain me why we take archive log backup when we have incremental backup everyday using RMAN in Oracle.
Regards,
Balaji
OK, suppose you take your incremental backup at 01:00 (one o'clock in the morning). Now suppose your database crashes at 09:00 (nine o'clock in the morning). How are you going to recover the transactions that occurred between 01:00 and 09:00? Your backup from 01:00 isn't going to reflect that activity.
And to add to it, the online backup isn't consistent to a given point-in-time, SCN. Data files are being modified even as they are being backed up. Suppose the backup process starts reading data file #1. Let's say it reads the first 50 blocks into a buffer, then starts writing them to the backup piece. But even as it is writing to the backup, some of those blocks get modified by DML going on in some other process. Those changes will not be in the backup, but they will be in the online redo logs and eventually written to the archive logs.
So, you tell me, why do we have archivelogs? Now, if they are needed for database recovery, where will you be if the archivelogs themselves are lost? Now, why do you suppose we might want backups of them as well?
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