Delta Load in CPI-DS

Hi CPI-DS experts,

I am new to DS and looking to execute a task(using preload and postload scripts) for Delta loads.I have a source DATASTORE as ECC using tables .For the initial run , I got few records from ECC. I changed one single record in ECC and executed the task again. Now I got all the records(with changed record as well) , where as I am looking ONLY for the single changed record in the second run.

Can someone throw light here on fetching ONLY modified records from ECC in the second run.Is that something need to managed at ECC or in DS.

Thanks in advance,