estimated row count for a pk range

[tommaso barbugli]

Hello,
Lately I collapsed several (around 1k) column families in a bunch (100) of
column families.
To keep data separated I have added an extra column (family) which is part
of the PK.

While previous approach allowed me to always have a clear picture of every
column family's size; now I have no other option than select all the rows
and make some estimation to guess the overall size used by one of the
grouped data in this CFs.

eg.
SELECT * FROM cf_shard1 WHERE family = '1';

Of course this does not work really well when cf_shard1 has some data in
it; is there some way perhaps to get an estimated count for rows matching
this query?

Thanks,
Tommaso