On 9/16/13 10:37 PM, Dolph Mathews wrote:
On Mon, Sep 16, 2013 at 5:31 AM, Michael Still <[email protected]
<mailto:[email protected]>> wrote:
On Fri, Sep 13, 2013 at 7:51 AM, Dolph Mathews
<[email protected] <mailto:[email protected]>> wrote:
> ++ Data backups are a solved problem, and no DB admin should
trust an
> application to perform its own backups.
I'm not completely sure I agree. Consider the case where a cloud with
active users undertakes an upgrade. The migrations run, and they allow
user traffic to hit the installation. They then discover there is a
serious problem and now need to rollback. However, they can't just
restore a database backup, because the database is no longer in a
consistent state compared with the hypervisors -- users might have
created or deleted instances for example.
In this scenario if we could downgrade reliably, they could force a
downgrade with db sync, and then revert the packages they had
installed to the previous version.
How would they handle this scenario with just database backups?
Great point, but I still wouldn't *rely* on an application to manage
it's own data backups :)
I don't think Michael was saying anybody should be relying on migrations
to manage its own backups but that it could serve an edge case that
database snapshots can not. In the scenario given I would imagine that
the administrators did have backups but wanted to avoid using them to
not lose any new data entered. If the migration downgrade were to fail
they would still have the backups and be no worse off than they would
have been without them. However if the migration downgrade works then
they get the benefit of not (necessarily) losing new user data.
Cheers,
Josh
--
Rackspace Australia
Michael
--
Rackspace Australia
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-Dolph
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