Hi Everyone

I have a question with regards read performance and schema design if someone could help please.

Our requirement is to store per user, many unique results (which is basically an attempt at some questions ..) so I had thought of having the userid as the row key and the result id as columns. 

The keys  for the result ids are maintained in a separate location so are known without having to perform any additional lookups.

My concern is that over time reading a single result would incur the overhead of reading the entire row from disk so gradually slow things down.

So I was considering if changing the row key to userid + result id would be a better solution ?