Re: Dired C idea

[Eric Abrahamsen]

Fabrice Bauzac-Stehly <noon@mykolab.com> writes:

> Michael Albinus <michael.albinus@gmx.de> writes:
>
>> Michael Albinus <michael.albinus@gmx.de> writes:
>>
>>>>   > Should be feasible. The hard part is a rule to determine, whether rsync
>>>>   > is better suited than the existing implementation, with the given 
>>>> actual
>>>>   > arguments. I suspect, that small directories and/or short files are
>>>>   > better served with the current implementation.
>>>>
>>>> Do we really need to decide this?  Wouldn't it be ok to use rsync
>>>> for all cases (where Tramp is not in use)?
>>>
>>> I would like to see some benchmark figures first. For example, I'm not
>>> sure that rsync performs better when the target directory does not exist
>>> yet, and there's nothing to sync.
>>
>> I made some comparison between "cp -pr" and "rsync -pr" on shell
>> level. I've copied the whole Emacs tree to somewhere else. First the
>> case, that the target does not exist:
>
> Beware, "cp -pr" preserves timestamps, while "rsync -pr" does not.
> You'd have to add "-t" to rsync, which should make it much quicker when
> the files are already there, because then rsync will trust stat(2)'s
> mtime and size, skipping the actual opening and scanning of the files'
> contents.  But if we don't trust this heuristics we would add
> --ignore-times.  Also if we want to skip the rsync checksum scanning, and
> mimic "cp" more, we can add --whole-file.  But it depends on what we
> want to do?
>
> The original use case of rsync is, of course, to synchronize things; in
> particular, it will not prompt the user before overwriting a file, which
> could be dangerous.  It can silently avoid overwrites with
> --ignore-existing, though.  For this reason, I'm not sure it would be
> wise to place it on the C key as replacement to the copy?
>
> Another area where rsync shines is the possibility to fine-tune the
> copying: --delete, rich filters on the sender and/or the receiver sides,
> --copy-dest...  But then, precise control over the options is required,
> so why not achieve that with the "!" key in Dired?
>
>   ! rsync -rt "--filter=-s *.dat" --delete * /tmp/ RET

Looks like a job for the newly merged transient library!