The Cassandra API supports batch mutations:

batch_mutate(keyspace, mutation_map, consistency_level): Executes the specified mutations on the keyspace. mutation_map is a map>>; the outer map maps the key to the inner map, which maps the column family to the Mutation; can be read as: map>>. To be more specific, the outer map key is a row key, the inner map key is the column family name. A Mutation specifies either columns to insert or columns to delete. See Mutation and Deletion above for more details.

Are all mutations that are executed in a batch executed atomically? So if one of the mutations fails, do the others fail too?