bug#2912: 23.0.92; Ediff over TRAMP too slow

bug#2912: 23.0.92; Ediff over TRAMP too slow

[Michael Albinus]

David Abrahams <dave@boostpro.com> writes:

> Ediff two remote files using /ssh:... protocol
>
> It seems to go over the network for everything.  At first I thought it
> was the auto-refining, but I turned that off and it didn't seem to make
> any difference in speed.

In case of remote files, ediff compares local copies, indeed. I'm not so
familiar with ediff, therefore I don't know, whether this can be changed
easily, running the diff command on the remote host. However, this
introduces more complexity into ediff: there might be protocols which do
not support execution of remote commands (like ftp or smb). Furthermore,
ediff would need to check, whether the files to be compared reside on
the same remote host.

I don't believe that this shall be changed before the release of Emacs
23.1. After the release, it might be a new feature somebody (with more
skills than I have on ediff) might implement.

For larger files, I recommend to use the scp method instead of ssh.

Best regards, Michael.

bug#2912: 23.0.92; Ediff over TRAMP too slow

[David Abrahams]

On Apr 7, 2009, at 3:44 AM, Michael Albinus wrote:

> David Abrahams <dave@boostpro.com> writes:
>
>> Ediff two remote files using /ssh:... protocol
>>
>> It seems to go over the network for everything.  At first I thought  
>> it
>> was the auto-refining, but I turned that off and it didn't seem to  
>> make
>> any difference in speed.
>
> In case of remote files, ediff compares local copies, indeed.

If that's all it was doing, I wouldn't be complaining.  Each time I  
move to the next diff, it appears to be going over the network.

> I'm not so
> familiar with ediff, therefore I don't know, whether this can be  
> changed
> easily, running the diff command on the remote host. However, this
> introduces more complexity into ediff: there might be protocols  
> which do
> not support execution of remote commands (like ftp or smb).  
> Furthermore,
> ediff would need to check, whether the files to be compared reside on
> the same remote host.

I don't think that would be a big win.  There is, however, a lot to be  
gained somewhere *during* the ediff session.

> I don't believe that this shall be changed before the release of Emacs
> 23.1. After the release, it might be a new feature somebody (with more
> skills than I have on ediff) might implement.
>
> For larger files, I recommend to use the scp method instead of ssh.


Really!  I thought they were roughly the same.  Thanks for the hint.

--
David Abrahams
BoostPro Computing
http://boostpro.com

bug#2912: 23.0.92; Ediff over TRAMP too slow

[Michael Albinus]

David Abrahams <dave@boostpro.com> writes:

> I don't think that would be a big win.  There is, however, a lot to be
> gained somewhere *during* the ediff session.

As I said, I'm not familiar with ediff. But there might also be another
reason for network activity. If the files are under vc control, a lot of
checks are always performed silently. You won't see the checks for local
files, because they are fast enough. But for remote files it matters.

If you know, that your files are *not* under vc control, you might apply

  (setq vc-handled-backends nil)

Best regards, Michael.

bug#2912: 23.0.92; Ediff over TRAMP too slow

[David Abrahams]

On Apr 7, 2009, at 9:29 AM, Michael Albinus wrote:

> David Abrahams <dave@boostpro.com> writes:
>
>> I don't think that would be a big win.  There is, however, a lot to  
>> be
>> gained somewhere *during* the ediff session.
>
> As I said, I'm not familiar with ediff. But there might also be  
> another
> reason for network activity. If the files are under vc control, a  
> lot of
> checks are always performed silently.

Wow, you're right!  Ediff'ing files not under vc control is very snappy!
OK, this is weird: now I can't reproduce the problem even for files  
under version control.

I'll let you know if I find out anything more, but I guess we can  
ignore this one for now.

Thanks,
--
David Abrahams
BoostPro Computing
http://boostpro.com

bug#2912: 23.0.92; Ediff over TRAMP too slow

[Stefan Monnier]

>>> Ediff two remote files using /ssh:... protocol
>>> It seems to go over the network for everything.  At first I thought it
>>> was the auto-refining, but I turned that off and it didn't seem to make
>>> any difference in speed.
>> In case of remote files, ediff compares local copies, indeed.
> If that's all it was doing, I wouldn't be complaining.  Each time I move to
> the next diff, it appears to be going over the network.

I cannot reproduce this here.  I opened two remote files (via Tramp/SSH)
and called M-x ediff-buffers, then killed Tramp's internal buffer and
moved from diff to diff (via ediff's frame using keys like `n' and SPC)
and it did not try to reconnect to the remote machine.


        Stefan