Yes and no. It depends on what if you are able to limit or plan how large the number of comments and size of them would be - as well as if you expect any kind of filtering or ordering on these.
It would be simple to have the user id and a map/list of their comments attached to that record - but you then need to worry about reaching the record limit if you are using a persistent storage backed namespace (not in-memory only) FAQ - Write Block Size .
Another alternative would be to write all of the comments into their own set, and have a bin you can create a secondary index on to query against.
So questions:
- how big is each comment/related data stored with it?
- how many comments do you expect per user (peak)?
- how many total users do you expect (peak)?