[Dirvish] using --inplace ?

[Dave Howorth]

Paul Slootman wrote:
> I was chekcing what rsync does in a typical dirvish run. Basically lots
> of stat()s of the file in the destination directory, stat()s of the file
> in the link-dest directory, then (when the file doesn't yet exist) an
> open() for writing in the destination directory with a temporary
> filename, and then a rename() at the end.

What does it do in the case where the file does exist but has changed?

> I considered that the use of a temp name and then a rename doesn't
> really make much sense in dirvish usage. Since rsync 2.6.3 (30 Sep 2004)
> it knows about --inplace.

But according to the man page, I think we can only use it from 2.6.4 
onwards:
"Prior to rsync 2.6.4 --inplace was also incompatible with 
--compare-dest and --link-dest."

> This will save 2 system calls per new or
> changed file. Doesn't sound like much, but it's a lot of metadata
> updates that will impact journalling filesystems.

I'm all for saving system calls (and context switches :) so this sounds 
like a good idea.

> Can anyone think of a reaon why using it would be a bad idea, besides
> the fact that an older rsync version may be in place (pun intended),
> in which case it should be upgraded anyway?
> 
> I've actually modified dirvish already on one of the systems I have
> dirvish running on to use --inplace, I'll check tomorrow how it went.

It always comes down to how to know something didn't break, doesn't it?

Cheers, Dave