Best way to determine if a user has viewed data

Question

What is the best method to determine if a user has viewed a piece of data, ie like an update to a comment. The two solutions I have thought about are these....

1. Use a separate table that has a row for each user and the data id that is being viewed and inserting into when the item was last viewed.

2. Use the same table and add a row for every user when the item is changed and delete that row when the user actually views the data.

Both methods solve the problem but in solution 2 the maximum rows for the table would at worst equal that of solution 1, no one viewed anything, and at best has 0 rows, everything has been viewed. I know in solution 2 you have no way to determine when it was viewed.

Thoughts?

Edit: I was using an update to a comment as an example. In the actual application, new users wouldn't be expected to view or read old data. It would mean nothing to them for they just joined.

Answer 1

It's got to be option 1:

Table 1 (comment)

• comment_id
• comment

Table 2 (comment_view)

• comment_id
• user_id

Option 2 will not work because every new user will have every existing comment "marked read."