Peeking Under the Hood - Learning Apache Cassandra - page 276

The wide row data structure
Another important observation is that, at the column family level, there is no preset list of
allowed cell names. The cell names we observe in alice 's partition of the
home_status_updates column family are derived partially from data calculated at
runtime—namely, the UUID values of various status update ID columns. At the CQL level,
tables must have predefined column names but no equivalent restriction exists at the
column family level.
Looking closely at the cells in alice 's RowKey , we observe that they are in order: first,
descending by the timestamp encoded in the UUID component of the cell name, and
second, alphabetically ascending by the column name component. You learned in Chapter
3 , Organizing Related Data that clustering columns give CQL rows a natural ordering, and
now we know how the cells grouped under a given RowKey at the column family level are
always ordered by the cell name.
The data structure that we observe at alice 's RowKey in home_status_updates is
commonly called a wide row . Not to be confused with the rows we commonly interact
with in CQL tables, wide rows are simply ordered collections of cells; each wide row is as-
sociated with a RowKey, which at the CQL level we call a partition key.