Discretely writable collections

While it's useful for records to be internally structured into discrete fields, a given property of a record isn't always a single value such as a string or an integer. One simple way to handle fields that contain collections of values is to serialize them using a format such as JSON and then save the serialized collection into a text field. However, in order to update collections stored in this way, the serialized data must be read from the database, decoded, modified, and then written back to the database in its entirety. If two clients try to perform this kind of modification to the same record concurrently, one of the updates will be overwritten by the other. For this reason, many databases offer built-in collection structures that can be discretely updated: values can be added to and removed from collections without reading and rewriting the entire collection. Cassandra is no exception, offering list, set, and map collections, and supporting operations such as append the number 3 to the end of this list. Neither the client nor Cassandra itself needs to read the current state of the collection in order to update it, meaning collection updates are also blazingly efficient.