rsync - Nov 2004 - Feature suggestion: --write-batch --dry-run

AFAICS, --write-batch logs the changes made while doing an rsync
operation from place A to place B, and lets you then use the batch file
to apply those changes to place C if it were hitherto the same as B. I
reckon it'd be a good feature to have a mode where the changes can be
logged *without* updating B, so that the update to B itself can be done
from the batch file.

The motivation for this is wanting to synchronise a large directory tree
between Site A and Site B. They can only communicate directly through a
slow network link, but I often *visit* Site B from Site A while carrying
several Gbytes' worth of Ipod.

So it would be cool if Site A could use the network connection to work
out what needed doing, but not actually send any new files over --
instead just writing a batch file which I could then carry over to B and
apply. (I can't just rsync Site A onto my Ipod, and then rsync it again
at the other end, because the Ipod is much smaller than the total size
of the directory tree, even though it's much larger than any one update
would be. Nor do I really want to have *two* copies of the directory
tree at Site A in order to use traditional --write-batch.)

Even better, of course, would be to find out that this sort of operation
was *already* possible using some rsync features I missed when looking
into this...

	Peter

On Thu, Nov 25, 2004 at 06:48:58PM +0000, Peter Hartley
wrote:
> Even better, of course, would be to find out that this sort of operation
> was *already* possible using some rsync features I missed when looking
> into this...
The only way to do this at the moment is to do a local update of an
identical set of destination files, and create a batch file from that
update.  In other words, you need an identical copy of the remote files
on a local system (either the same system as the source of real
transfer, or somewhere on its local net).  To ensure that this local set
of files is identical to the old files on the remote system you'll
either need to ensure that the remote files don't change between
updates, or you'll need to do a reverse rsync of the remote-host's files
to the local-host's duplicate copy (and hope that this update is small
enough to complete in a reasonable amount of time).  Then, create a
batch file by updating the local copy of the remote server's files.
Transport the batch file to the remote site and use --read-batch to make
an identical update on the remote system.  That brings the two
hierarchies back into sync, and readies the setup for the next update.

I've entered an enhancement suggestion into bugzilla that requests that
--write-batch and --dry-run be allowed to work together to create a
batch file without updating the remote system.

..wayne..