On Tue, 25 Oct 2011 17:46:43 -0400
Phil Stracchino <alaric AT metrocast DOT net> wrote:

> On 10/25/11 10:41, Konstantin Khomoutov wrote:
> >> MySQLdump is a valid technique, and the simplest working technique.
> >> You should not, as a rule, back up the MySQL data directory at
> >> filesystem level.  It is extremely unlikely to yield a consistent
> >> backup.  If you're going to attempt this, issue a FLUSH TABLES WITH
> >> READ LOCK, snapshot the MySQL directory, release the lock, then
> >> mount the snapshot and back up the snapshot.  Thanks to InnoDB's
> >> write-ahead logs and crash recovery features, this technique is
> >> generally safe *IF ALL YOUR DATABASES ARE IN INNODB TABLES*.
> > I'm not that sure regarging your claim: [1] does not indicate FTWRL
> > does not work for MyISAM databases and [2] directly contradicts your
> > claim by stating that certain things FTWRL does it's doing exactly
> > to accomodate MyISAM peculiarities.
> I'm not for a moment asserting that FLUSH ...  doesn't work on MyISAM.
> It actually works more reliably on MyISAM than on InnoDB.  My point is
> that should you get a glitch - perhaps something wasn't fully flushed
> to disk before your snapshot - InnoDB has built-in features to
> recover from the error.  MyISAM does not.  MyISAM is, in fact, very
> vulnerable to data corruption from any of a number of causes.
Sorry for being picky, but you seem to blame MyISAM for its property
which has nothing to do with hot backups (via FTWRL).  The only point
of FTWRL is to make the database file to be coherent with the internal
(in-memory) state of its database, and then that file is backed up
simply by open/read+read.../close cycle which only deals with the
filesystem and is not at all concerned with the flush really
succeeded in bringing the data to the disk's platters.
Transaction log is not involved in this technique as it serves a
completely orthogonal task.

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