Number of columns per row for composite columns?

[hlqv]

Hi everyone,
I'm confused with number of columns in a row of Cassandra, as far as I know
there is 2 billions columns per row. Like that if I have a composite column
name in each row, for ex: (timestamp, userid), then number of columns per
row is the number of distinct 'timestamp' or each distinct 'timestamp,
userid' is a column?