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Re: tramp (2.1.15); Unclear doc for rsync method

From: Kai Großjohann
Subject: Re: tramp (2.1.15); Unclear doc for rsync method
Date: Mon, 13 Apr 2009 20:32:44 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b3pre) Gecko/20090223 Thunderbird/3.0b2

On 04/13/2009 11:56 AM, Michael Albinus wrote:
I'm not confident that we shall go this direction. There is currently
another discussion about cached file *attributes*, which run out of
date, when another process on the remote machine changes a file there. I
fear, we couldn't keep local file caches in sync without serious
supervision of changes on the remote side, etc.

I think in this case there is not much to worry about, since the worst case is no speed up in the file transfer.

If you do "rsync $REMOTE_FILE $LOCAL_FILE", and if rsync does not fail, then you can assume that after the command finishes, $LOCAL_FILE is an exact copy of $REMOTE_FILE. This assumption holds regardless of the previous contents of $LOCAL_FILE. So whichever version of the $REMOTE_FILE we chance to keep around, it will be fine. If our version is reasonably up to date, then the file transfer goes faster. If it is very wrong, then the file transfer goes at normal speed.

This discussion makes me wonder: What is the use of the rsync method? On the one hand, we guess that it is not useful, for most files being edited are small. On the other hand, if people explicitly choose the rsync method, then perhaps this is because they expect some benefit from it. And it is clear that they can expect any benefit when editing small files. So perhaps the rsync method user community is exactly that subset of the Tramp users who regularly edit large files remotely?

*scratches head*


PS: I just assume, but haven't tested, that "rsync $REMOTE_FILE $NEW_LOCAL_FILE" runs at about the same speed as "rsync $REMOTE_FILE $RANDOM_LOCAL_FILE" for the same $REMOTE_FILE. ($NEW_LOCAL_FILE is a file that does not exist, $RANDOM_LOCAL_FILE is an existing file with contents that are very different from the contents of the $REMOTE_FILE. Perhaps if $RANDOM_LOCAL_FILE is very large then this does not hold?)

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