Partial transferred files useless at resume, compare-dir can help ?

[Constantin Teodorescu]

So, my use case is :

1. lot of connections over dial-up lines
2. need to transfer safely  A SINGLE BZIPPED FILE to the server
3. if dial-up line fails, it's automatically restarted after 5 minutes 
and transfer start again

I heard about the --partial option in order to keep the partial 
transferred file. I thought that rsync will apply his incremental check 
and update alghoritm on that partial file and resume the transfer.

Unfortunatelly , the temporary file name is a unique file name ( 
.mydb-dump.sql.bz2.MkVSHy ) and in the next transfer session it will be 
another one  , so "partial" transfer files does not help me much.

Can "--compare-dir" help me?

I need a good , reliable , transfer of a binary file that can be resumed 
in the next transfer session if possible.
I need also a good and atomic "switch" of the new succesfull transfered 
file with the existing one, keeping (if possible) a backup file of it.

The workstations are using rsync version 2.6.3.pre1 with protocol 
version 28 , the server is using rsync  version 2.6.8  protocol version 29.

Thanks for the help,
Teo