Here you got a good explaination of how the counters work. 

Video : 
Sildes :

I think it will answer your question and help you understanding interesting things about counters.

If you need a short answer, it concurrency will be handled nicely and you'll have the expected result.


2012/3/14 Tamar Fraenkel <>

My apologies for the naive question, but I am new to Cassandra and even more to counter columns.

If I have a counter column, what happens if two threads are trying to increment it's value at the same time for the same key?


Tamar Fraenkel 
Senior Software Engineer, TOK Media