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archivelogmode

Posted on 2014-04-04
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Last Modified: 2014-04-08
By default online redologs are recorded in flashback recovery area.

Then what is the purpose of setting database to archivelog mode.
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Question by:tonydba
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slightwv (䄆 Netminder) earned 500 total points
ID: 39978199
As online redo logs fill up they are archived off in archive log mode.

This is necessary for point in time recovery.

If they are not archived off, the online redo logs are overwritten when it is their turn again.
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by:David
ID: 39978299
Oracle has Concept material to help if you need this in-depth.  High level, data modification statements (DML) in Oracle are copied into a redo log.  When the statement is committed, the change is written into the physical datafile, and copied into one or more archive logs -- presuming the database instance is running in archivelog mode.

As slight points out, the redo mechanism is round-robin.  There is no long-term retention, except for the archive logs.

Also, by allowing multiple archivelog destinations, including to other hosts, Oracle provides redundancy.  Loss from a single backup medium is no longer catastrophic.
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by:Alexander Eßer [Alex140181]
ID: 39978875
Loss from a single backup medium is no longer catastrophic.
As long as your Oracle DB runs with archivelog mode = on ;-)
This is/should be the default setting within productive environments. TEST, DEV and most other DB instances can be used without archivelog mode turned on.
At least this is how I/we used to work ;-)
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by:David
ID: 39979071
Tony, we may have strayed from your question.  The "point" of archivelog mode is to enable the recovery of one's database to a system change event (SCN) or point in time. All data manipulation is recorded,  then replicated to provide multiple backups.  Archivelog mode is required for flashback.  Example, a user mistakenly drops a table.  With flashback enabled, the restoration of that table is quick and simple.

Many decision support / data warehouse systems, on the other hand, may not need to recover at will.  They might restore to a full backup point, then apply incremental changes -- or to re-run the extract/data/load (ETL) jobs that feed into the database.  It may be more practical to repeat a data import than to archive everything.

Does that help?
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Author Closing Comment

by:tonydba
ID: 39986477
Thank you...
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