NIFI connector to RDBMS

[אבישי דה מאיו]

Hello,
We would like to use Apache NIFI in order to stream data from one database to 
another in our organization. ( db2 mainframe to mssql server )
In order to do so we would wish to understand of how NIFI is listening to the 
events occur in the source table ?
Does NIFI uses CDC under the hood ? Triggers ?
What is the risks involving streaming on a large scale tables ?
Thank you in advnce,
Avishai