help create column family in cassandra-cli refers to old, unsupported options.
- memtable_operations: Number of operations in millions before the memtable
is flushed. Default is memtable_throughput / 64 * 0.3
- memtable_throughput: Maximum size in MB to let a memtable get to before
it is flushed. Default is to use 1/16 the JVM heap size.