On Sun, Jun 13, 2010 at 9:29 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Sun, Jun 13, 2010 at 07:10:30PM -0400, Ilia Mirkin wrote:
>> On Sun, Jun 13, 2010 at 6:47 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>> > On Sat, Jun 12, 2010 at 01:00:52AM -0400, Ilia Mirkin wrote:
>> >> Sorry to pick up an old-ish thread, but I have a similar situation:
>> >> On Sun, May 23, 2010 at 9:19 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>> >> > On Sun, May 23, 2010 at 09:23:44AM -0500, Roman Kononov wrote:
>> >> >> On 2010-05-23, 20:18:56 +1000, Dave Chinner <david@xxxxxxxxxxxxx>
>> >> >> wrote:
>> >> >> > Can you find out what the application is triggering this?
>> >> I noticed this happening with mysql and xtrabackup -- the latter opens
>> >> up mysql's files while mysql is still running (and modifying its own
>> >> files) and backs them up in a (hopefully) safe way.
>> > That's not safe at all - there's no guarantee you'll end up with a
>> > consistent database image doing backups like this. Have you ever
>> > tried to restore and use one of these backups?
>> Yep, works great. [Used it to initialize a slave, did the full
>> checksums, so it's unlikely to have randomly corrupt data.]
> You were lucky, I'd say. xtrabackup is supposed to be tightly
> integrated with mysql, so perhaps it should be using the same IO
> methods that the admin has selected for their database. Maybe you
> need to talk to the xtrabackup folks to get them to add a "backup
> via direct IO" method if the mysql database is using direct IO so
> that other uses don't have the same issues.
Maybe. We've been using this technique, although on a different
physical machine and with ext3, for quite some time (and we verify all
backups). I did notice that there is a minor difference in
configuration, esp wrt direct IO, so I'll check it out in more detail.
[We're now setting innodb_flush_method to O_DIRECT whereas we weren't
before... although based on the documentation and a cursory
understanding of how xtrabackup works, this shouldn't be harmful.]
> And from a "I read it on the interwebs so it must be true"
> perspective, without a loud obnoxious warning we'll never hear about
> problems until someone flames us about silent data corruption on a
> random blog that gets slashdotted and then referenced for the next
> 10 years as the next canonical "XFS eats my data!" reference for the
Instead it will be "mysql works fine on ext3, but with xfs it spams
the logs with warnings, therefore xfs must be broken". I don't think
there's anything realistically that you can do about uninformed users
and FUD. Although I wasn't suggesting to get rid of the warning,
rather to make it more explicit as to what it's warning about. I
interpret a WARN as a BUG that can be recovered but where the
underlying system needs a careful look; my first inclination after
seeing a fs-related WARN would be to take the system down and run an
fsck. What's happening here seems more akin to getting a WARN when
calling an ioctl with invalid parameters.