Cassandra Practice Test

In the context of logical modeling rules, what does the term "clustering columns" refer to?

1. Attributes that determine uniqueness

2. Attributes used for partitioning data

3. Attributes used for sorting within partitions

4. Attributes that cannot be changed

The correct answer is: Attributes used for sorting within partitions

Clustering columns are specifically designed to define how data is sorted or organized within a partition in a Cassandra database. When you create a table, the combination of partition key columns and clustering columns determines the layout of the data on disk. The partition key identifies which partition the data belongs to, while clustering columns dictate the order in which rows are stored within that partition. This means that if multiple rows share the same partition key, the clustering columns will determine their sequence within that partition. For example, if you have a partition key for a user and a clustering column for timestamps, all of the user's data can be sorted chronologically due to the clustering column. This sorting capability is essential for efficiently executing queries that retrieve data in a specific order or need ranged queries within partitions, enhancing the performance of read operations. Clustering columns do not by themselves ensure uniqueness; that role is primarily fulfilled by the combination of partition keys and clustering columns. They also can be modified, which distinguishes them from immutable attributes within the data model. Thus, the term "clustering columns" clearly corresponds to attributes used for sorting data within specific partitions.