--itemize-changes not recursive (not printing created files inside created directories)

[Perry Hutchison]

Paul Slootman <paul+rsync at wurtel.net> wrote:

> On Wed 18 Dec 2013, Kevin Korb wrote:
> > Also, rsync's -c is rather dumb as it computes checksums for files
> > that have different sizes so they can't possibly be the same and it
> > computes checksums for files that only exist on one end and therefore
> > has nothing to compare them to.
>
> The list of files on the source is generated and transferred to the
> destination before rsync knows that the destination file is different.
>
> To make rsync checksum only the files with same size would mean changing
> the filesystem scan to a two-pass thing (send the list of filenames plus
> their sizes, wait for the destination to tell you what files need
> checksumming, do that and send the filenames again, now with checksum
> data), and retransferring file metadata again.

That seems to imply that avoiding unnecessary checksum calculations
would double the protocol overhead, which I think is overly pessimistic.

IIUC, the current protocol, without checksums, amounts to (greatly
simplified):

    Sender                    Receiver

    I have (name1,meta1)
    (name2,meta2), ...

                              I need #s 3,8,13, ...

    Send requested files

                              Write files to destination as received

To do checksums only when needed:

    Sender                    Receiver

    Checksums have
    been requested.
    I have (name1,meta1)
    (name2,meta2), ...

                              Based on sizes, I know
                              I need #s 3,13, ...
                              and I may need (#5,checksum5),
                              (#8,checksum8), ...

    Send known-needed

    For each "may need"
        compute checksumN
        if match
           send "#N matches"
        else
           send "#N no match"
           send #N data

                              Write files to destination as received

If that is "a two-pass thing", the current protocol must involve
1.9 passes :)