Live DB backups with rsync?

[jw schultz]

On Tue, Jan 14, 2003 at 03:44:26PM -0400, Steve Mallett wrote:
> Is it possible to do live backups of a running DB with rsync???
> 
> I was just talking to livevault.com & they (only on win boxes) say they 
> can grab changes from a client's live DB & sync them remotely.
> 
> It sounded like BS to me, but I'm neither a DB guy or sync'ing expert.

On it's face It sounds like worse the BS.  Depending on
which BS you can either grow roses or enjoy "the way we
were".

Generally MS OSs you can't even rsync an open file.  As
such, to sync tablespaces you have to shut down the
database.

It could be they are using something like debase where you
use a set of libraries to access the data files directly and
there is no back end running.  The files are only accessed
during transactions so you could squeeze an rsync in
between accesses.  I believe the the MS Access DB[sic] works
this way.

A service oriented database (Oracle, SQLserver, pgsql,
mysql, etc) keeps the files open all the time and even if
you can read them the database will be inconsistent.

What you may be able to do is to rsync the commit log.  This
is a common practice in *IX systems.  On windows it may be
problematic doing this because of locking on open files.
This method does work and by replaying the logs whenever
they change can be used to keep a running copy of the
database almost up-to-date to allow for a limited (the most
recent transactions may be lost) fail-over capability.



-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt