|CQL data modeling|
An advantage of indexes is the operational ease of populating and maintaining the index. Indexes are built in the background automatically, without blocking reads or writes. Client-maintained tables as indexes must be created manually; for example, if the artists column had been indexed by creating a table such as songs_by_artist, your client application would have to populate the table with data from the songs table.
To perform a hot rebuild of an index, use the nodetool utility rebuild_index command.