I think this is a very simple question and might have been asked before.... but couldn't find answer elsewhere.... Sorry if it is repetitive. We are trying to use Cassandre and i am stuck in the datamodel.....

Do we have indexed table? i see some classes but dont know what they will be used for.... Is the index tell Casandra where exactly the column and the value in the column family is located? Say i do a query for which i dont have the rowid, i am looking for and i want to get a value of a coumn with a specific value.... will the secoundry index help on it? or should i use lucene to do that?

What exactly the index will do and help on? 

Thanks in advance.... May be i am confused because my understanding is completely wrong abt the index.