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Donald K. Burleson

Oracle Tips

Oracle Log Buffer

Oracle creates redo logs for all update operations.  In case of disk failure, the redo logs are used to roll forward, since they contain the after image of all row changes.                             

First, the after images are written to the log buffer area of RAM.  The LGWR background process then transfers the images to Oracle online redo log files. In the last step, the ARCH background process writes the online redo log files to the archived redo log file system, where they are available to recover the database in the event of disk failure. 

However, some shops avoid this overhead by using triple-mirrored disks and running their databases in NOARCHIVELOG mode.  These shops believe the high redundancy is sufficient protection from a disk crash, and they deliberately reject the ability to roll the database forward, in return for faster performance.

The above text is an excerpt from "Creating a Self Tuning Oracle Database", by Rampant TechPress.  It is only $9.95 and all scripts in this tips can be immediately downloaded.


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