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Re: Unison hangs on copy

On Sat, Jul 23, 2011 at 09:21:22AM -0400, Randy Kramer wrote:
> On Saturday 23 July 2011 08:25:10 am Roger Leigh wrote:
> > I use unison several times a day to sync over 100GiB of data.
> > I see it stall quite frequently.  I think it's a bug in unison,
> > possibly timing related.  I see it only when syncing over the
> > internet on a DSL connection, not over a LAN.
> Don't know if this helps, but if unison uses rsync (which, iirc, someone 
> mentioned it does), you should be aware that rsync has quite a bit 
> of "overhead" (in some sense) to determine exactly which pieces of a 
> file are different and then transmits only those.  
> So, again, iirc, it does calculations both at the rsync server and the 
> rsync client to get "checksums" (not quite the word I'm looking for, 
> but close) of pieces of the file on both ends, then exchanges those 
> checksums to see where differences exist, then exchanges the necessary 
> pieces of the file, and finally reassembles the file.
> With very large files, it is not surprising to see the link quiet for 
> periods of time while calculations are being done at each end.
> (I once read the academic thesis that the author of rsync wrote about 
> the rsync algorithm--I don't accurately remember the details, but what 
> I wrote above gives the general idea.)

In this case, there are no big files or many files involved, so it
doesn't seem to be the problem.


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