Re: ArchiveMode and log_archive_start Questions

Some simple questions are posed and answered:

Jonathan Gennick wrote:

> >(1) On my instance, the log mode is ARCHIVE but the log_archive_start is
> >set to false. The log files weren't being archived. How is the ARCHIVE
> >mode and the log_archive_start parameter related and how can the mode be
> >ARCHIVE when it doesn't archive the log files automatically?

> It's just because Oracle designed things that way. The way
> you are running requires you to manually archive the log
> files. Now why in the world you would want to manually do
> that, I have no idea. Perhaps there is some historical
> reason, and someone who has worked with Oracle longer than I
> have might be able to explain it.

Perhaps I can.

ARCHIVELOG mode just *requires* that logs be archived before they are re-used (overwritten). NOARCHIVELOG mode will happily overwrite logs.

But you can *require* the logs to be archived without having it be automatic. For example, you have a server machine with a single tape drive that is not dedicated to Oracle use, and you have a tape that is your archive destination.

If you archive automatically, then Oracle will either demand that the right tape be mounted all the time, or will write to whatever tape is mounted, all on Oracle's own schedule. This will make your OS backups grumpy.

Instead you might have a few dozen online redo logs (enough to allow operations to continue without archiving for several hours at your usual database throughput) and you manually (or via cron) kick off the archiving activity when you know the right tape is mounted and nobody else is using the tape drive.

Connect to your database with Server Manager and issue the command 'archive log list' to see what's up.

Note that you can also have automatic archiving turned on, but run in NOARCHIVELOG mode. This means you have a background thread, ARCH, sitting around doing nothing, because nobody ever asks it to archive any logs, because you aren't archiving. This is a mostly harmless scenario.

Cheers.
 -Tom

Received on Mon Apr 05 1999 - 16:39:32 CDT