can rsync scan files only with mtime since T?

[Matt McCutchen]

On 8/24/07, Jamie Lokier <jamie at shareable.org> wrote:
> A really nice solution would be for rsync to use the rsync delta
> transmission algorithm (or something like it) to compare the set of
> file attributes between each end.

I think this is an excellent idea, but it will take a considerable
amount of care to implement.  To benefit from the delta transfer while
maintaining correctness, the two sides need to generate file-list
representations of a file F that are identical *if and only if* F
needs no changes in the destination.

An example of an area in which this is tricky is permissions when
--perms is off.  If F exists on the destination, its permissions there
won't be changed, so a moot difference between F's source and
destination permissions shouldn't prevent F's file-list entries from
being matched.  Thus, the file-list entries participating in the delta
transfer can't contain permissions.  But if it is discovered during
the file-list transfer that a file G exists in source but not
destination, the sender has to go back and send the source G's
permissions so the receiver can create the destination G with the
correct permissions.  Thus, two phases are required: initial file-list
matching and supplemental attributes.  The supplemental attributes
could be done in the existing file transfer phase.

In addition, the interactions between file-list delta-transfer and
incremental recursion will have to be worked out.

Matt