Patch: Offline transfer mode

[Steve Traugott]

In offline mode, with only one destination, each batch file is
cumulative -- there is no sequence.  Lose one, just regenerate it.  Old
batches are useless -- don't keep them laying around and you won't be
tempted to try to apply them again.  (It might be perfectly safe to
always say 'rsync --read-batch=foo ... && rm foo').  Applying only the
most recent batch multiple times appears to cause no harm (anyone know
for sure?).  From the patched man page I posted:

    [...] It is safe to create a batch file multiple times without
    applying it to the destination. It is safe to lose the removable
    media and the batch file it contains; just run with --offline again
    to regenerate it. It even appears safe to accidentally try to apply
    the same batch file to the destination multiple times -- as of this
    writing we haven't seen this cause problems beyond the warning
    messages this generates.

The intended use of batch mode, without offline, and with *multiple*
destinations, is trickier, because it requires that the human and/or
admin scripts have the discipline to *always* apply *all* of the batches
to *all* of the machines in the right order.  You can't easily
regenerate the same batch, because --write-batch without --offline
changes the reference destination in the act of creating the batch.  Old
batches have to be kept until applied to all machines, then there's the
problem of down machines, new machines, etc.  It's a variant of the
"push" problem in automated systems administration -- see
http://www.infrastructures.org/bootstrap/pushpull.shtml.

I haven't thought through the possible use of --write-batch and
--offline *together* with multiple destinations; I suspect it reduces
the risks somewhat because it's easier to regenerate the most recent
batch, but all of the ordering and reliability problems of the previous
paragraph are probably still there.

Steve

On Mon, Mar 21, 2005 at 07:08:56AM -0800, Keith Lofstrom wrote:
> 
> The batch and offline transfer methods sound useful.  Question:
> what happens if batch files are missing, or applied out-of-sequence?
> Humans are not as accurate as TCP.
> 
> Keith
> 
> -- 
> Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
> KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
> Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs
> -- 
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-- 
Stephen G. Traugott  (KG6HDQ)
UNIX/Linux Infrastructure Architect, TerraLuna LLC
stevegt at TerraLuna.Org 
http://www.stevegt.com -- http://Infrastructures.Org
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