How to eliminate from Data Scraping OF Same page Multiple time

Assume that in a product of Amazon 5000 comments present in today and i scrap whole comments and stored this 5000 comments in Database.The next day total no of comment will become 5050.
i don’t want to scrap whole 5050 comments again (previous 5000 + 50 new) and then compare it with database or eliminate duplicate data.(because it will take more time)
i want to do scrap only new 50 comments and then store it to data base.how can i do it??

Please Help

hi…
please help me to solve the above issue.