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тАО06-12-2002 09:49 PM
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тАО06-12-2002 10:12 PM
тАО06-12-2002 10:12 PM
SolutionImagine a database crash. You want to recover your database up to the last committed data. You restore your last fullbackup and start playing back ... the redologs. And that's the reason. Funny as it may sound, but for Oracle it's more important (relatively speaking off course :-) that the redolog gets written than that the actual database page gets written.
Hope this explains,
Tom
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тАО06-12-2002 10:14 PM
тАО06-12-2002 10:14 PM
Re: Why oracle LGWR process should write redo log file before DBW0 process flush buffer cache?
While oracle is running, it allows processes to update data in the memory structure rather than update data on the disk due to the cost increase. While this is helpful on the surface by increasing the speed at which a process will come back to you, it does mean that what the database on disk is and what is true in memory is not in sync.
The reason the the checkpoint is flushed at that point, is so that the log in question is concurrent with the database, and can be used in a recovery situation (if that log were the last log used in a point-in-time recovery). Checkpoints can be forced either manually, or by setting the "LOG_CHECKPOINT_TIMEOUT" or "LOG_CHECKPOINT_INTERVAL" in the init.ora.
I hope this answers some of your questions.
Thanks,
Brian
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тАО06-12-2002 11:59 PM
тАО06-12-2002 11:59 PM
Re: Why oracle LGWR process should write redo log file before DBW0 process flush buffer cache?
next to data integrity, which already has been mentioned, think about SPEED!
A data block might get updated in memory several times before effectively being written to disk.
regards,
Thierry.
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тАО06-14-2002 02:46 AM
тАО06-14-2002 02:46 AM
Re: Why oracle LGWR process should write redo log file before DBW0 process flush buffer cache?
When a user issues a COMMIT, LGWR puts a commit record in the redo log buffer and flushes the entire buffer to disk. The so called "fast commit" mechanism. Oracle can record a successful commit even though the data blocks have not yet been written to disk.
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тАО06-23-2002 11:38 PM
тАО06-23-2002 11:38 PM