Counter Columns in Cassandra

A counter data type is a special kind of column whose user-visible value is a 64-bit signed integer used to store a number that incrementally counts the occurrences of a particular event. Counter column tables must use counter data type. Counters can be stored in dedicated tables only, and you cannot create an index on a counter column.
INSERT statements are not allowed on counter tables and so we must use an UPDATE statement to update the counter column

• Don't assign the counter data type to a column that serves as the primary key
• Don't use the counter data type in a table that contains anything other than counter data types and primary keys
• Don't use the counter data type to generate sequential numbers for surrogate keys; use the timeuuid data type instead

create counter_table {
   rowkey ascii,
   counterfield counter,
   primary key (rowkey)
};
update counter_table set counterfield = counterfield + 1
where rowkey = '1';

Reference:
http://www.datastax.com/dev/blog/whats-new-in-cassandra-2-1-a-better-implementation-of-counters