I am designing database for a Forum kind of application. The use cases involves showing unread topics for an user. So, I require to keep track of read/unread status for each post for each user id.

I have users and posts table. I am thinking I should created 'Read\_Posts' table with userid and postid, so I can add each post user has seen to this table. But, over time this table will become very huge. 

Any other alternate approaches to this?

Thanks!