2000-08-08-11:33:04 Fran�ois Pinard:
> [...] I'm using a modem link [...]
> I'm facing compression:
> * at the PPP level,
> * at the ssh level,
> * at the rsync level.
>[...]
> Adding RSYNC compression in such context does not seem any useful
> to me.
I disagree. Well-chosen compression protocols won't inflate the data
by more than a couple of percent, insignificant, if it's already
compressed and so incompressible. I'd expect that of any deployed
compression implementation, at any layer.
So extra compression doesn't hurt, at least as long as CPU is way
way ahead of the game, as with modern CPUs that stay on the
exponential performance improvement curve, in the eternally doomed
attempt to make Windows run fast, pushing bits over modems that
banged into shannon's wall years back and just plain stopped getting
faster.
While the lower levels of compression won't help any, neither will
they hurt noticeably, when you apply compression at a higher layer
of the protocol stack.
I'd expect that rsync would be able to do a better job of
compression, even if it's applying the same basic compression
algorithm, just because it knows more about the structure of the
data and so can apply it more wisely. And the rsync man page
concurs:
Note this this option typically achieves better compression
ratios that can be achieved by using a compressing remote
shell, or a compressing transport, as it takes advantage of
the implicit information sent for matching data blocks.
-Bennett
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