rsync - Aug 2004 - rsync "-I" vs. "-c"

If I use the "-I" to ignore date and size as quick-check methods of 
determining
change, what method does it use to determine difference?  If it falls 
back to
checksumming the entire file, maybe the manpage might warn that this 
would be
as expensive as using the "-c" option...or not depending on what it
uses for
determining difference at that point.

So exactly how does rsync compare files for differences when date & size are
used but checksumming is not?

Thanks!
-Linda

On Sun, Aug 01, 2004 at 06:20:11PM -0700, Linda A. W.
wrote:
> If I use the "-I" to ignore date and size as quick-check methods
of
> determining
just modtime.  rsync never ignores size differences.
> change, what method does it use to determine difference?  If it falls 
> back to
> checksumming the entire file, maybe the manpage might warn that this 
> would be
> as expensive as using the "-c" option...or not depending on what
it uses for
> determining difference at that point.
Short answer:  It does fall back to checksum comparison.

Long answer:  I'm not sure, but I suspect that the reason this is not so
explicit in the man page is that it's a bit complicated in the code,
too.  I _think_ that using -I would be even more expensive than -c,
because it will take longer to eventually do the same checksum
comparison.

But, Wayne knows these options like the back of his hand.  Wayne?

-chris
> 
> So exactly how does rsync compare files for differences when date &
size are
> used but checksumming is not?
> 
> Thanks!
> -Linda
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On Sun, Aug 01, 2004 at 06:20:11PM -0700, Linda A. W.
wrote:
> If I use the "-I" to ignore date and size as quick-check methods
of
> determining change, what method does it use to determine difference?
With -I, rsync does no advance determination of sameness, it just
transfers all the files and lets the matching data make the transfer as
small as possible.  This is more expensive than -c if all the files are
the same (since the receiving side reads the file twice and writes it
once for each file), but could be slightly faster than -c if most of the
files have changes (since the -c option makes the receiving side read the
file thrice and write it once when it is different, but only reads the
file once if it is the same).
> So exactly how does rsync compare files for differences when date &
> size are used but checksumming is not?
When date & size are used, rsync skips the file when the modify time and
the size is identical on the receiver and the sender for a given file.

..wayne..