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Re: lost of redo logs

From: Jeff <jeff_at_work.com>
Date: Mon, 04 Mar 2002 14:36:23 GMT
Message-ID: <a600p7$5th$1@cronkite.cc.uga.edu>


In article <a5urpj$ibt$1_at_lust.ihug.co.nz>, "Howard J. Rogers" <dba_at_hjrdba.com> wrote:
>Why? When a log switch occurs, that signals (1) DBWR to flush all buffers
>dirtied by the redo stream contained within the log just filled (ie, a check
>point event) and the CKPT process to stamp the header of the affected data
>files and (2) ARCH to take a copy of the log just filled. Two completely
>separate events, and both capable of finishing independently of each other.
>Yet the log remains active until *both* events report successful completion.
>So you could have an active log that has long-since been archived, but a
>sluggish DBWR and/or CKPT are still chugging away doing their thing. Hence,
>active and archived. Or, DBWR and/or CKPT could do their stuff at
>lightening speed, but ARCH runs into trouble writing to the archive
>destination (by the far the more common scenario)... hence, active and
>unarchived. It's this last one where the loss of an active log would not
>*necessarily* require recovery... because the data files have received a new
>SCN from CKPT, those transactions don't need to be recovered using redo
>contained in the lost log.

Why wouldn't a log-switch checkpoint be sufficient to make the current logfile inactive? (Ignore the archiving side of it, as that's happening successfully.)

I've got an 8.1.7.3 database on a Solaris box where the previously "current" logfile remains "active" until another logswitch or checkpoint occurs. Reading the above and the documentation, I'm led to believe that the checkpoint that happens at a log switch should be sufficient to take the log from "current" to "inactive" (again, ignoring the archiving side of it). Why then does it take TWO checkpoints to make a logfile inactive? Received on Mon Mar 04 2002 - 08:36:23 CST

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