Re: [Duplicity-talk] Rsync Backend

[Matthias-Christian Ott]

On Wed, 30 Dec 2009 14:53:54 +0100
"Peter Valdemar Mørch (Lists)" <address@hidden> wrote:

> Richard Scott richard-at-pointb.co.uk |Lists/Send to lists| wrote:
> > I'm guessing that your running mysqldump each night to dump to a flat 
> > file? If so, duplicity will see this "flat file" as a brand new file 
> > (each night) and take a full backup of it (each night) :-( I think its 
> > something to do with the file having a different inode or something?
> > 
> > If anyone else on this list as a different view, please shout :-)
> 
> SHOUT! I'm not certain of the insides of duplicity, but I understand it, 
> and as my experience with duplicity shows:
> 
> Because it use librsync, large files that change only little lead to 
> small backups, irrespective of inode or whatever.
> 
> Perhaps the mysqldump output contains many timestamps or other things, 
> that make these large files very different. But if they're similar, that 
> should lead to small incremental backups.

The rsync algorithm works on fixed block sizes [1], so you can always
construct pathological cases where inserting some bytes causes a huge
incremental backup.

Regards,
Matthias-Christian

[1] http://dspace-prod1.anu.edu.au/bitstream/1885/40765/2/TR-CS-96-05.pdf