Database file rsync - any way to tell it to rsync against the last file?

[Eberhard Moenkeberg]

Hi,

On Fri, 12 Nov 2004, Michael Bourgon wrote:

> My apologies if this has been asked before - I searched the archives
> but couldn't find it, probably because I'm not sure what terms to use.
> 
> I'm trying to rsync database backups from point A to point B, where
> point B has rsync running as a service.
> 
> Every day I make a new backup on point A (mike_db_20041110.bak), and
> since there's no matching file on point B, the entire file is sent
> over.  But since these are backups of the same database, the
> difference between mike_db_20041110.bak and the prior backup,
> (mike_db_20041109.bak), should be fairly minor.
> 
> Is there any way to tell it that I want to rsync mike_db_20041110.bak,
> using mike_db_20041109.bak as a source, so that when I'm done I still
> have both files?  I could build a script to rename them to the same
> filename, but I'd rather let rsync do the work if possible.

Do a
  ln mike_db_20041109.bak mike_db_20041110.bak
before the rsync.
The time stamps should be different by nature, so rsync would communicate 
block checksums even if the sizes are equal, and transfer only the changed 
blocks

> p.s. one other question - I know that Rsync compresses the file, but
> does it look at the whole file first, then send?  The speeds I'm
> getting sending these bak files doesn't look like it's being
> compressed - the end file grows by about 10mb a minute, which is far
> less than we should get with our T1.  And if it looks at the whole
> file first, I should be seeing 10-to-1 compression.

Compression is a transfer option. No influence on file comparision.

Cheers -e
-- 
Eberhard Moenkeberg (emoenke at gwdg.de, em at kki.org)