Determines which filter predicates can be pushed down to Cassandra.
The list of predicates to be pushed down is available in predicatesToPushDown property.
The list of predicates that cannot be pushed down is available in predicatesToPreserve property.
list of filter predicates available in the user query
Cassandra table definition
Returns the set of predicates that cannot be pushed down to Cassandra,
so they must be applied by Spark
Returns the set of predicates that can be safely pushed down to Cassandra