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Re: System snapshots



|| On Mon, 10 Jan 2005 18:40:39 +0100
|| Petter Reinholdtsen <pere@hungry.com> wrote: 

pr> [Otavio Salvador]
>> No because some applications doesn't depends only of configuration
>> files but data-files. When you purge then, all data files will be
>> removed together (in major of times). Another problem is how you can
>> revert upgrade processes in database files and like?

pr> RPM have a feature allowing it to do upgrade transactions and rollback
pr> of failed installs, where it will include the data files in the
pr> transaction log.  I read about this in the Linux Journal article
pr> "Transactions and Rollback with RPM" by James Oden,
pr> <URL:http://www.linuxjournal.com/article/7034>.

pr> Such feature would be nice to have in Debian as well.  If you have a
pr> very short upgrade window, where one will have to abort and roll back
pr> if the upgrade fail, it would be helpful if dpkg would allow you to
pr> roll back the upgrade.

Rollback upgrade is more simple then allow snapshot. Let me try to
clear what I think about it:

 If you want to allow rollback, you can do it using one transation to
 all involved packages with versioned depends and not ALL
 packages. Another issue is it will be available while you are
 upgrading and not later.

 Support it for later time is a lot more complicated because the data
 involved can be changed and you can't only revert to old data. You
 need to convert all changes to previous data. ie: PostgreSQL

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