If you have time, this will show you how counters internally work :http://blip.tv/datastax/counters-in-cassandra-5497678(video from Sylvain @CassandraSF2011)

If you just want to know what is possible to do or not with counters but not necessary why, better read thishttp://www.datastax.com/dev/blog/whats-new-in-cassandra-0-8-part-2-counters


2013/8/1 Kanwar Sangha <kanwar@mavenir.com>

Hi We are struggling to understand how the counter family maintains consistency in Cassandra.

Say Counter1 value is 1 and it is read by 2 clients at the same time who want to update the value. After both write, it will become 3 ?