Re: rsnapshot and gzip'ed mysql dumps

On Wed, Aug 09, 2006 at 04:34:41PM -0700, Malcolm Frazier wrote:
> Hi,
> 
> I am wondering how rsnapshot works with compressed MySQL dumped files. 
> So say I dump a database using mysqldump and gzip it up how will 
> rsnapshot rotate that? how will it compare the difference between one 
> compressed mysql dump and another?

It makes a difference to rsync whether you compress the dump files.
This can affect the network bandwidth used and the running time.

If they are uncompressed, rsync can generally make use of commonalities
with the previous dump file to avoid transferring every block of the
new dump file.  But with compressed files, as soon as you change one 
byte in the original file, you cannot expect to find any commonalities
after that point in the compressed files.  (Unless you use special 
compression techniques.)

But it doesn't make any difference to the way rsnapshot does rotation -
if a file has changed at all (either in content or metadata) then 
rsnapshot will end up with a new copy of the file (rather than a
hard link with a previous file) which will take up more disk space.

So the decision to compress or not to compress boils down to a trade-off 
between network traffic versus disk space.

___________________________________________________________________________
 David Keegel <djk@xxxxxxxxxxxxxxxxxx>  http://www.cyber.com.au/users/djk/
 Cybersource P/L: Linux/Unix Systems Administration Consulting/Contracting

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