cassandra - composite column keys & composite row keys -

i'm trying understand concept of composite column key & composite row key unable it. think it's used getting range of values can't use timestamp column cluster key purpose ? use case, advantages, disadvantages & implementation. please explain using cql 3.

composite column key: http://i.stack.imgur.com/qlbok.png

composite row key: http://i.stack.imgur.com/xa6hz.png

maybe confuse both terms refers how cassandra stores compounds primary keys. i'll explain how composite keys works , how stored physically cassandra 2.0 , cql3.

cassandra stores logical rows same partition key single physical wide row. partition key divided in (partition_key, clustering_key).

• partition_key: identifies row in cassandra. registers same partition_key go same machine , store together. can compound partition_key.
• clustering_key: keep data same partition_key ordered. can set multiple clustering keys separated commas.

imagine have table purchase definition:

create table purchase(   user text,   item text,   time timestamp,   primary key ((user, item), time) ); 

and data

john  car  09/01/14... john  car 09/05/13... john  house 09/07/11... penny laptop  09/08/08... penny laptop 09/03/11... rachel tv 09/01/09... 

cassandar store data

john || car  || 09/05/13 - 09/01/14 john || house || 09/07/11 penny || laptop || 09/08/08 - 09/03/11 rachel || tv || 09/01/09 

if want retrieve cars john bought can assure 2 registers stored , ordered time.

for querys have set partition key fields ( = ) , can if want compare order of clustering keys ( < or > ).

examples:

• select * purchase user='penny' , item='laptop'. return 2 registers.
• select * purchase user='john' , item='car' date 01/01/14. return 1 register.

hope helps.