File bit synchronization?

[Robert Fitzpatrick]

Not sure if that is the correct terminology. I have an rsync setup of
files between two Windows servers using cwRsync, which uses -apv options
among --progress and --delete options. One part of the backup is to
transfer a MSSQL backup file and I notice that after the initial
transfer taking 20 minutes or more, subsequent daily transfers after is
changes each night take only a minute or two max and this is the
summary...

Number of files: 1
Number of files transferred: 1
Total file size: 448610816 bytes
Total transferred file size: 448610816 bytes
Literal data: 3807632 bytes
Matched data: 444803184 bytes
File list size: 77
File list generation time: 0.001 seconds
File list transfer time: 0.000 seconds
Total bytes sent: 148389
Total bytes received: 3892615

Although the file size does not change very much day to day, the file is
generated from MSSQL backup function every day and does change, and the
destination date time stamp updates to match the source. If I wipe out
the file on the destination and start again, several minutes to transfer
the file. So, I assume there is some sort of 'bit synchronization' that
only refreshes the file contents? This is a binary file and I did not
know this was possible.

I've been running rsync between unix/linux boxes for years doing backup
and would love this to work with our PostgreSQL backups. I've tried the
same options and choosing pg_dump format options of both 'c' and
'p' (plain text), but nothing works. It always transfers the entire
file. I'm I seeing this correctly that rsync can do this? If so, what
are the requirements to make it happen?

Thanks for the help...
-- 
Robert