Re: [rdiff-backup-users] more experiments, + apology

[David Kempe]

----- "Marcel (Felix) Giannelia" <address@hidden> wrote:
> Regardless, parts of what I said are still true (very small patches 
> between increments), but it's looking now more like something's 
> confusing the rsync algorithm itself, rather than rdiff-backup. There
> 
> are files in the backup set that seem to change daily (zipped backups
> 
> that Moodle produces), but only by a few bytes. Most of the file stays
> 
> exactly the same, but trying to use rdiff by itself on any pair of
> them 
> causes a patch that's just as big as the file. Somehow, putting
> several 
> of them together in a tar file (even gzipped) clues rdiff/rsync in to
> 
> the similarities, and then it can make a decent patch.


Hi Marcel,
I have solved this problem with the --rsyncable option to gzip when creating 
the gzip files. 
frmo the manpage:
       --rsyncable
              While compressing, synchronize the output occasionally based  on
              the  input.   This  increases  size  by less than 1 percent most
              cases, but means that the rsync(1) program can much  more  effi‐
              ciently  synchronize  files  compressed  with this flag.  gunzip
              cannot tell the difference between  a  compressed  file  created
              with this option, and one created without it.

which makes a big difference, as gzip will compress files almost completely 
differently if they have changed slightly if you don't use this option (in my 
experience - like for pg_dump and mysqldump)


dave