This page lists difficulties and peculiarities of Cassandra Storage Engine. I'm not putting them into bug tracker because it is not clear whether these properties should be considered bugs.
No way to get E(#rows in column family)
There seems to be no way to get even a rough estimate of how many different keys are present in a column family. I'm using an arbitrary value of 1000 now, which causes
- EXPLAIN will always show rows=1000 for full table scans. In the future, this may cause poor query plans.
DELETE FROM tablealways prints "1000 rows affected", with no regards how many records were actually there in the table.
MariaDB [j1]> delete from t1; Query OK, 1000 rows affected (0.14 sec)
We could use the new engine-independent-table-statistics feature to get some data statistics.