preventing rsync transfers

[Matt McCutchen]

On Thu, 2006-02-23 at 00:06 -0500, Peter wrote:
> Now I'm thinking: What if these operations overlap?  What can I do to
> prevent this?  Or is this even a problem to begin with?

I don't think anything will go seriously wrong, although you may get
some strange effects.  The main one is that the backup rsync might back
up half-uploaded temporary files from the upload rsync.  They will have
names like .filename.A1B2C3; you could give the backup rsync an exclude
filter of .*.* to keep these files out of backups.

If you want to ensure that the operations don't overlap, you have a few
options.  You could rig up your own system based on a shared lock file.
If both uploaders and backers-up use rsync daemons, you have additional
options.  You could use a module-level lock file with a max connections
limit of 1.  If rsync is changed so a daemon doesn't start if its pid
file is already in use (as I have just suggested in bug 3554), you could
use several daemons with the same pid file.
-- 
Matt McCutchen
hashproduct at verizon.net
http://hashproduct.metaesthetics.net/