You must first define the way you will capture the changes in the LIVE_DB.

What is the retention policy of this,

you can partition your data by datetime and have a full load to the rep_db

or can have logical deletion in REP_DB

Again, the question is what means you will use to detect the changes?

If you want to go with logical deletion use SCD techniques , also you need the changes capyture abiity.

It can be done through audit, triggers , row version etc..